mirror of
https://github.com/daveallie/crosspoint-reader.git
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Improve EPUB cover image quality with pre-scaling and Atkinson dithering (#116)
## Summary * **What is the goal of this PR?** Replace simple threshold-based grayscale quantization with ordered dithering using a 4x4 Bayer matrix. This eliminates color banding artifacts and produces smoother gradients on e-ink display. * **What changes are included?** - Add 4x4 Bayer dithering matrix for 16-level threshold patterns - Modify `grayscaleTo2Bit()` function to accept pixel coordinates and apply position-based dithering - Replace simple `grayscale >> 6` threshold with ordered dithering algorithm that produces smoother gradients ## Additional Context * Bayer matrix approach: The 4x4 Bayer matrix creates a repeating pattern that distributes quantization error spatially, effectively simulating 16 levels of gray using only 4 actual color levels (black, dark gray, light gray, white). * Cache invalidation: Existing cached `cover.bmp` files will need to be deleted to see the improved rendering, as the converter only runs when the cache is missing.
This commit is contained in:
Eunchurn Park
GitHub
parent
e3d0201365
commit
f96b6ab29c
@ -3,6 +3,126 @@
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#include <cstdlib>
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#include <cstring>
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// ============================================================================
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// IMAGE PROCESSING OPTIONS - Toggle these to test different configurations
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// ============================================================================
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// Note: For cover images, dithering is done in JpegToBmpConverter.cpp
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// This file handles BMP reading - use simple quantization to avoid double-dithering
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constexpr bool USE_FLOYD_STEINBERG = false; // Disabled - dithering done at JPEG conversion
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constexpr bool USE_NOISE_DITHERING = false; // Hash-based noise dithering
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// Brightness adjustments:
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constexpr bool USE_BRIGHTNESS = false; // true: apply brightness/gamma adjustments
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constexpr int BRIGHTNESS_BOOST = 20; // Brightness offset (0-50), only if USE_BRIGHTNESS=true
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constexpr bool GAMMA_CORRECTION = false; // Gamma curve, only if USE_BRIGHTNESS=true
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// ============================================================================
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// Integer approximation of gamma correction (brightens midtones)
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static inline int applyGamma(int gray) {
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if (!GAMMA_CORRECTION) return gray;
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const int product = gray * 255;
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int x = gray;
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if (x > 0) {
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x = (x + product / x) >> 1;
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x = (x + product / x) >> 1;
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}
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return x > 255 ? 255 : x;
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}
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// Simple quantization without dithering - just divide into 4 levels
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static inline uint8_t quantizeSimple(int gray) {
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if (USE_BRIGHTNESS) {
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gray += BRIGHTNESS_BOOST;
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if (gray > 255) gray = 255;
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gray = applyGamma(gray);
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}
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return static_cast<uint8_t>(gray >> 6);
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}
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// Hash-based noise dithering - survives downsampling without moiré artifacts
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static inline uint8_t quantizeNoise(int gray, int x, int y) {
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if (USE_BRIGHTNESS) {
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gray += BRIGHTNESS_BOOST;
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if (gray > 255) gray = 255;
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gray = applyGamma(gray);
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}
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uint32_t hash = static_cast<uint32_t>(x) * 374761393u + static_cast<uint32_t>(y) * 668265263u;
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hash = (hash ^ (hash >> 13)) * 1274126177u;
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const int threshold = static_cast<int>(hash >> 24);
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const int scaled = gray * 3;
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if (scaled < 255) {
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return (scaled + threshold >= 255) ? 1 : 0;
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} else if (scaled < 510) {
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return ((scaled - 255) + threshold >= 255) ? 2 : 1;
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} else {
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return ((scaled - 510) + threshold >= 255) ? 3 : 2;
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}
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}
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// Main quantization function
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static inline uint8_t quantize(int gray, int x, int y) {
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if (USE_NOISE_DITHERING) {
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return quantizeNoise(gray, x, y);
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} else {
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return quantizeSimple(gray);
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}
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}
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// Floyd-Steinberg quantization with error diffusion and serpentine scanning
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// Returns 2-bit value (0-3) and updates error buffers
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static inline uint8_t quantizeFloydSteinberg(int gray, int x, int width, int16_t* errorCurRow, int16_t* errorNextRow,
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bool reverseDir) {
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// Add accumulated error to this pixel
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int adjusted = gray + errorCurRow[x + 1];
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// Clamp to valid range
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if (adjusted < 0) adjusted = 0;
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if (adjusted > 255) adjusted = 255;
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// Quantize to 4 levels (0, 85, 170, 255)
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uint8_t quantized;
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int quantizedValue;
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if (adjusted < 43) {
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quantized = 0;
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quantizedValue = 0;
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} else if (adjusted < 128) {
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quantized = 1;
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quantizedValue = 85;
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} else if (adjusted < 213) {
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quantized = 2;
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quantizedValue = 170;
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} else {
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quantized = 3;
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quantizedValue = 255;
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}
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// Calculate error
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int error = adjusted - quantizedValue;
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// Distribute error to neighbors (serpentine: direction-aware)
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if (!reverseDir) {
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// Left to right
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errorCurRow[x + 2] += (error * 7) >> 4; // Right: 7/16
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errorNextRow[x] += (error * 3) >> 4; // Bottom-left: 3/16
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errorNextRow[x + 1] += (error * 5) >> 4; // Bottom: 5/16
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errorNextRow[x + 2] += (error) >> 4; // Bottom-right: 1/16
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} else {
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// Right to left (mirrored)
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errorCurRow[x] += (error * 7) >> 4; // Left: 7/16
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errorNextRow[x + 2] += (error * 3) >> 4; // Bottom-right: 3/16
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errorNextRow[x + 1] += (error * 5) >> 4; // Bottom: 5/16
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errorNextRow[x] += (error) >> 4; // Bottom-left: 1/16
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}
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return quantized;
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}
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Bitmap::~Bitmap() {
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delete[] errorCurRow;
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delete[] errorNextRow;
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}
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uint16_t Bitmap::readLE16(File& f) {
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const int c0 = f.read();
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const int c1 = f.read();
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@ -46,6 +166,8 @@ const char* Bitmap::errorToString(BmpReaderError err) {
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return "UnsupportedCompression (expected BI_RGB or BI_BITFIELDS for 32bpp)";
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case BmpReaderError::BadDimensions:
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return "BadDimensions";
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case BmpReaderError::ImageTooLarge:
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return "ImageTooLarge (max 2048x3072)";
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case BmpReaderError::PaletteTooLarge:
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return "PaletteTooLarge";
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@ -99,6 +221,13 @@ BmpReaderError Bitmap::parseHeaders() {
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if (width <= 0 || height <= 0) return BmpReaderError::BadDimensions;
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// Safety limits to prevent memory issues on ESP32
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constexpr int MAX_IMAGE_WIDTH = 2048;
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constexpr int MAX_IMAGE_HEIGHT = 3072;
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if (width > MAX_IMAGE_WIDTH || height > MAX_IMAGE_HEIGHT) {
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return BmpReaderError::ImageTooLarge;
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}
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// Pre-calculate Row Bytes to avoid doing this every row
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rowBytes = (width * bpp + 31) / 32 * 4;
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@ -115,21 +244,56 @@ BmpReaderError Bitmap::parseHeaders() {
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return BmpReaderError::SeekPixelDataFailed;
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}
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// Allocate Floyd-Steinberg error buffers if enabled
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if (USE_FLOYD_STEINBERG) {
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delete[] errorCurRow;
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delete[] errorNextRow;
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errorCurRow = new int16_t[width + 2](); // +2 for boundary handling
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errorNextRow = new int16_t[width + 2]();
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lastRowY = -1;
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}
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return BmpReaderError::Ok;
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}
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// packed 2bpp output, 0 = black, 1 = dark gray, 2 = light gray, 3 = white
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BmpReaderError Bitmap::readRow(uint8_t* data, uint8_t* rowBuffer) const {
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BmpReaderError Bitmap::readRow(uint8_t* data, uint8_t* rowBuffer, int rowY) const {
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// Note: rowBuffer should be pre-allocated by the caller to size 'rowBytes'
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if (file.read(rowBuffer, rowBytes) != rowBytes) return BmpReaderError::ShortReadRow;
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// Handle Floyd-Steinberg error buffer progression
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const bool useFS = USE_FLOYD_STEINBERG && errorCurRow && errorNextRow;
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if (useFS) {
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// Check if we need to advance to next row (or reset if jumping)
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if (rowY != lastRowY + 1 && rowY != 0) {
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// Non-sequential row access - reset error buffers
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memset(errorCurRow, 0, (width + 2) * sizeof(int16_t));
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memset(errorNextRow, 0, (width + 2) * sizeof(int16_t));
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} else if (rowY > 0) {
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// Sequential access - swap buffers
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int16_t* temp = errorCurRow;
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errorCurRow = errorNextRow;
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errorNextRow = temp;
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memset(errorNextRow, 0, (width + 2) * sizeof(int16_t));
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}
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lastRowY = rowY;
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}
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uint8_t* outPtr = data;
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uint8_t currentOutByte = 0;
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int bitShift = 6;
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int currentX = 0;
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// Helper lambda to pack 2bpp color into the output stream
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auto packPixel = [&](const uint8_t lum) {
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uint8_t color = (lum >> 6); // Simple 2-bit reduction: 0-255 -> 0-3
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uint8_t color;
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if (useFS) {
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// Floyd-Steinberg error diffusion
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color = quantizeFloydSteinberg(lum, currentX, width, errorCurRow, errorNextRow, false);
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} else {
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// Simple quantization or noise dithering
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color = quantize(lum, currentX, rowY);
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}
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currentOutByte |= (color << bitShift);
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if (bitShift == 0) {
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*outPtr++ = currentOutByte;
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@ -138,6 +302,7 @@ BmpReaderError Bitmap::readRow(uint8_t* data, uint8_t* rowBuffer) const {
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} else {
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bitShift -= 2;
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}
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currentX++;
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};
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uint8_t lum;
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@ -196,5 +361,12 @@ BmpReaderError Bitmap::rewindToData() const {
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return BmpReaderError::SeekPixelDataFailed;
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}
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// Reset Floyd-Steinberg error buffers when rewinding
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if (USE_FLOYD_STEINBERG && errorCurRow && errorNextRow) {
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memset(errorCurRow, 0, (width + 2) * sizeof(int16_t));
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memset(errorNextRow, 0, (width + 2) * sizeof(int16_t));
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lastRowY = -1;
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}
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return BmpReaderError::Ok;
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}
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@ -15,6 +15,7 @@ enum class BmpReaderError : uint8_t {
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UnsupportedCompression,
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BadDimensions,
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ImageTooLarge,
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PaletteTooLarge,
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SeekPixelDataFailed,
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@ -28,8 +29,9 @@ class Bitmap {
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static const char* errorToString(BmpReaderError err);
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explicit Bitmap(File& file) : file(file) {}
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~Bitmap();
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BmpReaderError parseHeaders();
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BmpReaderError readRow(uint8_t* data, uint8_t* rowBuffer) const;
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BmpReaderError readRow(uint8_t* data, uint8_t* rowBuffer, int rowY) const;
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BmpReaderError rewindToData() const;
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int getWidth() const { return width; }
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int getHeight() const { return height; }
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@ -49,4 +51,9 @@ class Bitmap {
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uint16_t bpp = 0;
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int rowBytes = 0;
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uint8_t paletteLum[256] = {};
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// Floyd-Steinberg dithering state (mutable for const methods)
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mutable int16_t* errorCurRow = nullptr;
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mutable int16_t* errorNextRow = nullptr;
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mutable int lastRowY = -1; // Track row progression for error propagation
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};
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@ -132,7 +132,9 @@ void GfxRenderer::drawBitmap(const Bitmap& bitmap, const int x, const int y, con
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isScaled = true;
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}
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const uint8_t outputRowSize = (bitmap.getWidth() + 3) / 4;
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// Calculate output row size (2 bits per pixel, packed into bytes)
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// IMPORTANT: Use int, not uint8_t, to avoid overflow for images > 1020 pixels wide
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const int outputRowSize = (bitmap.getWidth() + 3) / 4;
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auto* outputRow = static_cast<uint8_t*>(malloc(outputRowSize));
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auto* rowBytes = static_cast<uint8_t*>(malloc(bitmap.getRowBytes()));
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@ -154,7 +156,7 @@ void GfxRenderer::drawBitmap(const Bitmap& bitmap, const int x, const int y, con
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break;
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}
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if (bitmap.readRow(outputRow, rowBytes) != BmpReaderError::Ok) {
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if (bitmap.readRow(outputRow, rowBytes, bmpY) != BmpReaderError::Ok) {
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Serial.printf("[%lu] [GFX] Failed to read row %d from bitmap\n", millis(), bmpY);
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free(outputRow);
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free(rowBytes);
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@ -13,24 +13,296 @@ struct JpegReadContext {
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size_t bufferFilled;
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};
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// Helper function: Convert 8-bit grayscale to 2-bit (0-3)
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uint8_t JpegToBmpConverter::grayscaleTo2Bit(const uint8_t grayscale) {
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// Simple threshold mapping:
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// 0-63 -> 0 (black)
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// 64-127 -> 1 (dark gray)
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// 128-191 -> 2 (light gray)
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// 192-255 -> 3 (white)
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return grayscale >> 6;
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// ============================================================================
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// IMAGE PROCESSING OPTIONS - Toggle these to test different configurations
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// ============================================================================
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constexpr bool USE_8BIT_OUTPUT = false; // true: 8-bit grayscale (no quantization), false: 2-bit (4 levels)
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// Dithering method selection (only one should be true, or all false for simple quantization):
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constexpr bool USE_ATKINSON = true; // Atkinson dithering (cleaner than F-S, less error diffusion)
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constexpr bool USE_FLOYD_STEINBERG = false; // Floyd-Steinberg error diffusion (can cause "worm" artifacts)
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constexpr bool USE_NOISE_DITHERING = false; // Hash-based noise dithering (good for downsampling)
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// Brightness/Contrast adjustments:
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constexpr bool USE_BRIGHTNESS = true; // true: apply brightness/gamma adjustments
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constexpr int BRIGHTNESS_BOOST = 10; // Brightness offset (0-50)
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constexpr bool GAMMA_CORRECTION = true; // Gamma curve (brightens midtones)
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constexpr float CONTRAST_FACTOR = 1.15f; // Contrast multiplier (1.0 = no change, >1 = more contrast)
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// Pre-resize to target display size (CRITICAL: avoids dithering artifacts from post-downsampling)
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constexpr bool USE_PRESCALE = true; // true: scale image to target size before dithering
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constexpr int TARGET_MAX_WIDTH = 480; // Max width for cover images (portrait display width)
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constexpr int TARGET_MAX_HEIGHT = 800; // Max height for cover images (portrait display height)
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// ============================================================================
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// Integer approximation of gamma correction (brightens midtones)
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// Uses a simple curve: out = 255 * sqrt(in/255) ≈ sqrt(in * 255)
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static inline int applyGamma(int gray) {
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if (!GAMMA_CORRECTION) return gray;
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// Fast integer square root approximation for gamma ~0.5 (brightening)
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// This brightens dark/mid tones while preserving highlights
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const int product = gray * 255;
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// Newton-Raphson integer sqrt (2 iterations for good accuracy)
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int x = gray;
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if (x > 0) {
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x = (x + product / x) >> 1;
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x = (x + product / x) >> 1;
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}
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return x > 255 ? 255 : x;
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}
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// Apply contrast adjustment around midpoint (128)
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// factor > 1.0 increases contrast, < 1.0 decreases
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static inline int applyContrast(int gray) {
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// Integer-based contrast: (gray - 128) * factor + 128
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// Using fixed-point: factor 1.15 ≈ 115/100
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constexpr int factorNum = static_cast<int>(CONTRAST_FACTOR * 100);
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int adjusted = ((gray - 128) * factorNum) / 100 + 128;
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if (adjusted < 0) adjusted = 0;
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if (adjusted > 255) adjusted = 255;
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return adjusted;
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}
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// Combined brightness/contrast/gamma adjustment
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static inline int adjustPixel(int gray) {
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if (!USE_BRIGHTNESS) return gray;
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// Order: contrast first, then brightness, then gamma
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gray = applyContrast(gray);
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gray += BRIGHTNESS_BOOST;
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if (gray > 255) gray = 255;
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if (gray < 0) gray = 0;
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gray = applyGamma(gray);
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return gray;
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}
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// Simple quantization without dithering - just divide into 4 levels
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static inline uint8_t quantizeSimple(int gray) {
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gray = adjustPixel(gray);
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// Simple 2-bit quantization: 0-63=0, 64-127=1, 128-191=2, 192-255=3
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return static_cast<uint8_t>(gray >> 6);
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}
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// Hash-based noise dithering - survives downsampling without moiré artifacts
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// Uses integer hash to generate pseudo-random threshold per pixel
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static inline uint8_t quantizeNoise(int gray, int x, int y) {
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gray = adjustPixel(gray);
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// Generate noise threshold using integer hash (no regular pattern to alias)
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uint32_t hash = static_cast<uint32_t>(x) * 374761393u + static_cast<uint32_t>(y) * 668265263u;
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hash = (hash ^ (hash >> 13)) * 1274126177u;
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const int threshold = static_cast<int>(hash >> 24); // 0-255
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// Map gray (0-255) to 4 levels with dithering
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const int scaled = gray * 3;
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if (scaled < 255) {
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return (scaled + threshold >= 255) ? 1 : 0;
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} else if (scaled < 510) {
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return ((scaled - 255) + threshold >= 255) ? 2 : 1;
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} else {
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return ((scaled - 510) + threshold >= 255) ? 3 : 2;
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}
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}
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// Main quantization function - selects between methods based on config
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static inline uint8_t quantize(int gray, int x, int y) {
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if (USE_NOISE_DITHERING) {
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return quantizeNoise(gray, x, y);
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} else {
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return quantizeSimple(gray);
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}
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}
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// Atkinson dithering - distributes only 6/8 (75%) of error for cleaner results
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// Error distribution pattern:
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// X 1/8 1/8
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// 1/8 1/8 1/8
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// 1/8
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// Less error buildup = fewer artifacts than Floyd-Steinberg
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class AtkinsonDitherer {
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public:
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AtkinsonDitherer(int width) : width(width) {
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errorRow0 = new int16_t[width + 4](); // Current row
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errorRow1 = new int16_t[width + 4](); // Next row
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errorRow2 = new int16_t[width + 4](); // Row after next
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}
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~AtkinsonDitherer() {
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delete[] errorRow0;
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delete[] errorRow1;
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delete[] errorRow2;
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}
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uint8_t processPixel(int gray, int x) {
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// Apply brightness/contrast/gamma adjustments
|
||||
gray = adjustPixel(gray);
|
||||
|
||||
// Add accumulated error
|
||||
int adjusted = gray + errorRow0[x + 2];
|
||||
if (adjusted < 0) adjusted = 0;
|
||||
if (adjusted > 255) adjusted = 255;
|
||||
|
||||
// Quantize to 4 levels
|
||||
uint8_t quantized;
|
||||
int quantizedValue;
|
||||
if (adjusted < 43) {
|
||||
quantized = 0;
|
||||
quantizedValue = 0;
|
||||
} else if (adjusted < 128) {
|
||||
quantized = 1;
|
||||
quantizedValue = 85;
|
||||
} else if (adjusted < 213) {
|
||||
quantized = 2;
|
||||
quantizedValue = 170;
|
||||
} else {
|
||||
quantized = 3;
|
||||
quantizedValue = 255;
|
||||
}
|
||||
|
||||
// Calculate error (only distribute 6/8 = 75%)
|
||||
int error = (adjusted - quantizedValue) >> 3; // error/8
|
||||
|
||||
// Distribute 1/8 to each of 6 neighbors
|
||||
errorRow0[x + 3] += error; // Right
|
||||
errorRow0[x + 4] += error; // Right+1
|
||||
errorRow1[x + 1] += error; // Bottom-left
|
||||
errorRow1[x + 2] += error; // Bottom
|
||||
errorRow1[x + 3] += error; // Bottom-right
|
||||
errorRow2[x + 2] += error; // Two rows down
|
||||
|
||||
return quantized;
|
||||
}
|
||||
|
||||
void nextRow() {
|
||||
int16_t* temp = errorRow0;
|
||||
errorRow0 = errorRow1;
|
||||
errorRow1 = errorRow2;
|
||||
errorRow2 = temp;
|
||||
memset(errorRow2, 0, (width + 4) * sizeof(int16_t));
|
||||
}
|
||||
|
||||
void reset() {
|
||||
memset(errorRow0, 0, (width + 4) * sizeof(int16_t));
|
||||
memset(errorRow1, 0, (width + 4) * sizeof(int16_t));
|
||||
memset(errorRow2, 0, (width + 4) * sizeof(int16_t));
|
||||
}
|
||||
|
||||
private:
|
||||
int width;
|
||||
int16_t* errorRow0;
|
||||
int16_t* errorRow1;
|
||||
int16_t* errorRow2;
|
||||
};
|
||||
|
||||
// Floyd-Steinberg error diffusion dithering with serpentine scanning
|
||||
// Serpentine scanning alternates direction each row to reduce "worm" artifacts
|
||||
// Error distribution pattern (left-to-right):
|
||||
// X 7/16
|
||||
// 3/16 5/16 1/16
|
||||
// Error distribution pattern (right-to-left, mirrored):
|
||||
// 1/16 5/16 3/16
|
||||
// 7/16 X
|
||||
class FloydSteinbergDitherer {
|
||||
public:
|
||||
FloydSteinbergDitherer(int width) : width(width), rowCount(0) {
|
||||
errorCurRow = new int16_t[width + 2](); // +2 for boundary handling
|
||||
errorNextRow = new int16_t[width + 2]();
|
||||
}
|
||||
|
||||
~FloydSteinbergDitherer() {
|
||||
delete[] errorCurRow;
|
||||
delete[] errorNextRow;
|
||||
}
|
||||
|
||||
// Process a single pixel and return quantized 2-bit value
|
||||
// x is the logical x position (0 to width-1), direction handled internally
|
||||
uint8_t processPixel(int gray, int x, bool reverseDirection) {
|
||||
// Add accumulated error to this pixel
|
||||
int adjusted = gray + errorCurRow[x + 1];
|
||||
|
||||
// Clamp to valid range
|
||||
if (adjusted < 0) adjusted = 0;
|
||||
if (adjusted > 255) adjusted = 255;
|
||||
|
||||
// Quantize to 4 levels (0, 85, 170, 255)
|
||||
uint8_t quantized;
|
||||
int quantizedValue;
|
||||
if (adjusted < 43) {
|
||||
quantized = 0;
|
||||
quantizedValue = 0;
|
||||
} else if (adjusted < 128) {
|
||||
quantized = 1;
|
||||
quantizedValue = 85;
|
||||
} else if (adjusted < 213) {
|
||||
quantized = 2;
|
||||
quantizedValue = 170;
|
||||
} else {
|
||||
quantized = 3;
|
||||
quantizedValue = 255;
|
||||
}
|
||||
|
||||
// Calculate error
|
||||
int error = adjusted - quantizedValue;
|
||||
|
||||
// Distribute error to neighbors (serpentine: direction-aware)
|
||||
if (!reverseDirection) {
|
||||
// Left to right: standard distribution
|
||||
// Right: 7/16
|
||||
errorCurRow[x + 2] += (error * 7) >> 4;
|
||||
// Bottom-left: 3/16
|
||||
errorNextRow[x] += (error * 3) >> 4;
|
||||
// Bottom: 5/16
|
||||
errorNextRow[x + 1] += (error * 5) >> 4;
|
||||
// Bottom-right: 1/16
|
||||
errorNextRow[x + 2] += (error) >> 4;
|
||||
} else {
|
||||
// Right to left: mirrored distribution
|
||||
// Left: 7/16
|
||||
errorCurRow[x] += (error * 7) >> 4;
|
||||
// Bottom-right: 3/16
|
||||
errorNextRow[x + 2] += (error * 3) >> 4;
|
||||
// Bottom: 5/16
|
||||
errorNextRow[x + 1] += (error * 5) >> 4;
|
||||
// Bottom-left: 1/16
|
||||
errorNextRow[x] += (error) >> 4;
|
||||
}
|
||||
|
||||
return quantized;
|
||||
}
|
||||
|
||||
// Call at the end of each row to swap buffers
|
||||
void nextRow() {
|
||||
// Swap buffers
|
||||
int16_t* temp = errorCurRow;
|
||||
errorCurRow = errorNextRow;
|
||||
errorNextRow = temp;
|
||||
// Clear the next row buffer
|
||||
memset(errorNextRow, 0, (width + 2) * sizeof(int16_t));
|
||||
rowCount++;
|
||||
}
|
||||
|
||||
// Check if current row should be processed in reverse
|
||||
bool isReverseRow() const { return (rowCount & 1) != 0; }
|
||||
|
||||
// Reset for a new image or MCU block
|
||||
void reset() {
|
||||
memset(errorCurRow, 0, (width + 2) * sizeof(int16_t));
|
||||
memset(errorNextRow, 0, (width + 2) * sizeof(int16_t));
|
||||
rowCount = 0;
|
||||
}
|
||||
|
||||
private:
|
||||
int width;
|
||||
int rowCount;
|
||||
int16_t* errorCurRow;
|
||||
int16_t* errorNextRow;
|
||||
};
|
||||
|
||||
inline void write16(Print& out, const uint16_t value) {
|
||||
// out.write(reinterpret_cast<const uint8_t *>(&value), 2);
|
||||
out.write(value & 0xFF);
|
||||
out.write((value >> 8) & 0xFF);
|
||||
}
|
||||
|
||||
inline void write32(Print& out, const uint32_t value) {
|
||||
// out.write(reinterpret_cast<const uint8_t *>(&value), 4);
|
||||
out.write(value & 0xFF);
|
||||
out.write((value >> 8) & 0xFF);
|
||||
out.write((value >> 16) & 0xFF);
|
||||
@ -38,13 +310,49 @@ inline void write32(Print& out, const uint32_t value) {
|
||||
}
|
||||
|
||||
inline void write32Signed(Print& out, const int32_t value) {
|
||||
// out.write(reinterpret_cast<const uint8_t *>(&value), 4);
|
||||
out.write(value & 0xFF);
|
||||
out.write((value >> 8) & 0xFF);
|
||||
out.write((value >> 16) & 0xFF);
|
||||
out.write((value >> 24) & 0xFF);
|
||||
}
|
||||
|
||||
// Helper function: Write BMP header with 8-bit grayscale (256 levels)
|
||||
void writeBmpHeader8bit(Print& bmpOut, const int width, const int height) {
|
||||
// Calculate row padding (each row must be multiple of 4 bytes)
|
||||
const int bytesPerRow = (width + 3) / 4 * 4; // 8 bits per pixel, padded
|
||||
const int imageSize = bytesPerRow * height;
|
||||
const uint32_t paletteSize = 256 * 4; // 256 colors * 4 bytes (BGRA)
|
||||
const uint32_t fileSize = 14 + 40 + paletteSize + imageSize;
|
||||
|
||||
// BMP File Header (14 bytes)
|
||||
bmpOut.write('B');
|
||||
bmpOut.write('M');
|
||||
write32(bmpOut, fileSize);
|
||||
write32(bmpOut, 0); // Reserved
|
||||
write32(bmpOut, 14 + 40 + paletteSize); // Offset to pixel data
|
||||
|
||||
// DIB Header (BITMAPINFOHEADER - 40 bytes)
|
||||
write32(bmpOut, 40);
|
||||
write32Signed(bmpOut, width);
|
||||
write32Signed(bmpOut, -height); // Negative height = top-down bitmap
|
||||
write16(bmpOut, 1); // Color planes
|
||||
write16(bmpOut, 8); // Bits per pixel (8 bits)
|
||||
write32(bmpOut, 0); // BI_RGB (no compression)
|
||||
write32(bmpOut, imageSize);
|
||||
write32(bmpOut, 2835); // xPixelsPerMeter (72 DPI)
|
||||
write32(bmpOut, 2835); // yPixelsPerMeter (72 DPI)
|
||||
write32(bmpOut, 256); // colorsUsed
|
||||
write32(bmpOut, 256); // colorsImportant
|
||||
|
||||
// Color Palette (256 grayscale entries x 4 bytes = 1024 bytes)
|
||||
for (int i = 0; i < 256; i++) {
|
||||
bmpOut.write(static_cast<uint8_t>(i)); // Blue
|
||||
bmpOut.write(static_cast<uint8_t>(i)); // Green
|
||||
bmpOut.write(static_cast<uint8_t>(i)); // Red
|
||||
bmpOut.write(static_cast<uint8_t>(0)); // Reserved
|
||||
}
|
||||
}
|
||||
|
||||
// Helper function: Write BMP header with 2-bit color depth
|
||||
void JpegToBmpConverter::writeBmpHeader(Print& bmpOut, const int width, const int height) {
|
||||
// Calculate row padding (each row must be multiple of 4 bytes)
|
||||
@ -135,13 +443,59 @@ bool JpegToBmpConverter::jpegFileToBmpStream(File& jpegFile, Print& bmpOut) {
|
||||
Serial.printf("[%lu] [JPG] JPEG dimensions: %dx%d, components: %d, MCUs: %dx%d\n", millis(), imageInfo.m_width,
|
||||
imageInfo.m_height, imageInfo.m_comps, imageInfo.m_MCUSPerRow, imageInfo.m_MCUSPerCol);
|
||||
|
||||
// Write BMP header
|
||||
writeBmpHeader(bmpOut, imageInfo.m_width, imageInfo.m_height);
|
||||
// Safety limits to prevent memory issues on ESP32
|
||||
constexpr int MAX_IMAGE_WIDTH = 2048;
|
||||
constexpr int MAX_IMAGE_HEIGHT = 3072;
|
||||
constexpr int MAX_MCU_ROW_BYTES = 65536;
|
||||
|
||||
// Calculate row parameters
|
||||
const int bytesPerRow = (imageInfo.m_width * 2 + 31) / 32 * 4;
|
||||
if (imageInfo.m_width > MAX_IMAGE_WIDTH || imageInfo.m_height > MAX_IMAGE_HEIGHT) {
|
||||
Serial.printf("[%lu] [JPG] Image too large (%dx%d), max supported: %dx%d\n", millis(), imageInfo.m_width,
|
||||
imageInfo.m_height, MAX_IMAGE_WIDTH, MAX_IMAGE_HEIGHT);
|
||||
return false;
|
||||
}
|
||||
|
||||
// Allocate row buffer for packed 2-bit pixels
|
||||
// Calculate output dimensions (pre-scale to fit display exactly)
|
||||
int outWidth = imageInfo.m_width;
|
||||
int outHeight = imageInfo.m_height;
|
||||
// Use fixed-point scaling (16.16) for sub-pixel accuracy
|
||||
uint32_t scaleX_fp = 65536; // 1.0 in 16.16 fixed point
|
||||
uint32_t scaleY_fp = 65536;
|
||||
bool needsScaling = false;
|
||||
|
||||
if (USE_PRESCALE && (imageInfo.m_width > TARGET_MAX_WIDTH || imageInfo.m_height > TARGET_MAX_HEIGHT)) {
|
||||
// Calculate scale to fit within target dimensions while maintaining aspect ratio
|
||||
const float scaleToFitWidth = static_cast<float>(TARGET_MAX_WIDTH) / imageInfo.m_width;
|
||||
const float scaleToFitHeight = static_cast<float>(TARGET_MAX_HEIGHT) / imageInfo.m_height;
|
||||
const float scale = (scaleToFitWidth < scaleToFitHeight) ? scaleToFitWidth : scaleToFitHeight;
|
||||
|
||||
outWidth = static_cast<int>(imageInfo.m_width * scale);
|
||||
outHeight = static_cast<int>(imageInfo.m_height * scale);
|
||||
|
||||
// Ensure at least 1 pixel
|
||||
if (outWidth < 1) outWidth = 1;
|
||||
if (outHeight < 1) outHeight = 1;
|
||||
|
||||
// Calculate fixed-point scale factors (source pixels per output pixel)
|
||||
// scaleX_fp = (srcWidth << 16) / outWidth
|
||||
scaleX_fp = (static_cast<uint32_t>(imageInfo.m_width) << 16) / outWidth;
|
||||
scaleY_fp = (static_cast<uint32_t>(imageInfo.m_height) << 16) / outHeight;
|
||||
needsScaling = true;
|
||||
|
||||
Serial.printf("[%lu] [JPG] Pre-scaling %dx%d -> %dx%d (fit to %dx%d)\n", millis(), imageInfo.m_width,
|
||||
imageInfo.m_height, outWidth, outHeight, TARGET_MAX_WIDTH, TARGET_MAX_HEIGHT);
|
||||
}
|
||||
|
||||
// Write BMP header with output dimensions
|
||||
int bytesPerRow;
|
||||
if (USE_8BIT_OUTPUT) {
|
||||
writeBmpHeader8bit(bmpOut, outWidth, outHeight);
|
||||
bytesPerRow = (outWidth + 3) / 4 * 4;
|
||||
} else {
|
||||
writeBmpHeader(bmpOut, outWidth, outHeight);
|
||||
bytesPerRow = (outWidth * 2 + 31) / 32 * 4;
|
||||
}
|
||||
|
||||
// Allocate row buffer
|
||||
auto* rowBuffer = static_cast<uint8_t*>(malloc(bytesPerRow));
|
||||
if (!rowBuffer) {
|
||||
Serial.printf("[%lu] [JPG] Failed to allocate row buffer\n", millis());
|
||||
@ -152,13 +506,48 @@ bool JpegToBmpConverter::jpegFileToBmpStream(File& jpegFile, Print& bmpOut) {
|
||||
// This is the minimal memory needed for streaming conversion
|
||||
const int mcuPixelHeight = imageInfo.m_MCUHeight;
|
||||
const int mcuRowPixels = imageInfo.m_width * mcuPixelHeight;
|
||||
auto* mcuRowBuffer = static_cast<uint8_t*>(malloc(mcuRowPixels));
|
||||
if (!mcuRowBuffer) {
|
||||
Serial.printf("[%lu] [JPG] Failed to allocate MCU row buffer\n", millis());
|
||||
|
||||
// Validate MCU row buffer size before allocation
|
||||
if (mcuRowPixels > MAX_MCU_ROW_BYTES) {
|
||||
Serial.printf("[%lu] [JPG] MCU row buffer too large (%d bytes), max: %d\n", millis(), mcuRowPixels,
|
||||
MAX_MCU_ROW_BYTES);
|
||||
free(rowBuffer);
|
||||
return false;
|
||||
}
|
||||
|
||||
auto* mcuRowBuffer = static_cast<uint8_t*>(malloc(mcuRowPixels));
|
||||
if (!mcuRowBuffer) {
|
||||
Serial.printf("[%lu] [JPG] Failed to allocate MCU row buffer (%d bytes)\n", millis(), mcuRowPixels);
|
||||
free(rowBuffer);
|
||||
return false;
|
||||
}
|
||||
|
||||
// Create ditherer if enabled (only for 2-bit output)
|
||||
// Use OUTPUT dimensions for dithering (after prescaling)
|
||||
AtkinsonDitherer* atkinsonDitherer = nullptr;
|
||||
FloydSteinbergDitherer* fsDitherer = nullptr;
|
||||
if (!USE_8BIT_OUTPUT) {
|
||||
if (USE_ATKINSON) {
|
||||
atkinsonDitherer = new AtkinsonDitherer(outWidth);
|
||||
} else if (USE_FLOYD_STEINBERG) {
|
||||
fsDitherer = new FloydSteinbergDitherer(outWidth);
|
||||
}
|
||||
}
|
||||
|
||||
// For scaling: accumulate source rows into scaled output rows
|
||||
// We need to track which source Y maps to which output Y
|
||||
// Using fixed-point: srcY_fp = outY * scaleY_fp (gives source Y in 16.16 format)
|
||||
uint32_t* rowAccum = nullptr; // Accumulator for each output X (32-bit for larger sums)
|
||||
uint16_t* rowCount = nullptr; // Count of source pixels accumulated per output X
|
||||
int currentOutY = 0; // Current output row being accumulated
|
||||
uint32_t nextOutY_srcStart = 0; // Source Y where next output row starts (16.16 fixed point)
|
||||
|
||||
if (needsScaling) {
|
||||
rowAccum = new uint32_t[outWidth]();
|
||||
rowCount = new uint16_t[outWidth]();
|
||||
nextOutY_srcStart = scaleY_fp; // First boundary is at scaleY_fp (source Y for outY=1)
|
||||
}
|
||||
|
||||
// Process MCUs row-by-row and write to BMP as we go (top-down)
|
||||
const int mcuPixelWidth = imageInfo.m_MCUWidth;
|
||||
|
||||
@ -181,75 +570,164 @@ bool JpegToBmpConverter::jpegFileToBmpStream(File& jpegFile, Print& bmpOut) {
|
||||
return false;
|
||||
}
|
||||
|
||||
// Process MCU block into MCU row buffer
|
||||
// MCUs are composed of 8x8 blocks. For 16x16 MCUs, there are four 8x8 blocks:
|
||||
// Block layout for 16x16 MCU: [0, 64] (top row of blocks)
|
||||
// [128, 192] (bottom row of blocks)
|
||||
// picojpeg stores MCU data in 8x8 blocks
|
||||
// Block layout: H2V2(16x16)=0,64,128,192 H2V1(16x8)=0,64 H1V2(8x16)=0,128
|
||||
for (int blockY = 0; blockY < mcuPixelHeight; blockY++) {
|
||||
for (int blockX = 0; blockX < mcuPixelWidth; blockX++) {
|
||||
const int pixelX = mcuX * mcuPixelWidth + blockX;
|
||||
if (pixelX >= imageInfo.m_width) continue;
|
||||
|
||||
// Skip pixels outside image width (can happen with MCU alignment)
|
||||
if (pixelX >= imageInfo.m_width) {
|
||||
continue;
|
||||
}
|
||||
// Calculate proper block offset for picojpeg buffer
|
||||
const int blockCol = blockX / 8;
|
||||
const int blockRow = blockY / 8;
|
||||
const int localX = blockX % 8;
|
||||
const int localY = blockY % 8;
|
||||
const int blocksPerRow = mcuPixelWidth / 8;
|
||||
const int blockIndex = blockRow * blocksPerRow + blockCol;
|
||||
const int pixelOffset = blockIndex * 64 + localY * 8 + localX;
|
||||
|
||||
// Calculate which 8x8 block and position within that block
|
||||
const int block8x8Col = blockX / 8; // 0 or 1 for 16-wide MCU
|
||||
const int block8x8Row = blockY / 8; // 0 or 1 for 16-tall MCU
|
||||
const int pixelInBlockX = blockX % 8;
|
||||
const int pixelInBlockY = blockY % 8;
|
||||
|
||||
// Calculate byte offset: each 8x8 block is 64 bytes
|
||||
// Blocks are arranged: [0, 64], [128, 192]
|
||||
const int blockOffset = (block8x8Row * (mcuPixelWidth / 8) + block8x8Col) * 64;
|
||||
const int mcuIndex = blockOffset + pixelInBlockY * 8 + pixelInBlockX;
|
||||
|
||||
// Get grayscale value
|
||||
uint8_t gray;
|
||||
if (imageInfo.m_comps == 1) {
|
||||
// Grayscale image
|
||||
gray = imageInfo.m_pMCUBufR[mcuIndex];
|
||||
gray = imageInfo.m_pMCUBufR[pixelOffset];
|
||||
} else {
|
||||
// RGB image - convert to grayscale
|
||||
const uint8_t r = imageInfo.m_pMCUBufR[mcuIndex];
|
||||
const uint8_t g = imageInfo.m_pMCUBufG[mcuIndex];
|
||||
const uint8_t b = imageInfo.m_pMCUBufB[mcuIndex];
|
||||
// Luminance formula: Y = 0.299*R + 0.587*G + 0.114*B
|
||||
// Using integer approximation: (30*R + 59*G + 11*B) / 100
|
||||
gray = (r * 30 + g * 59 + b * 11) / 100;
|
||||
const uint8_t r = imageInfo.m_pMCUBufR[pixelOffset];
|
||||
const uint8_t g = imageInfo.m_pMCUBufG[pixelOffset];
|
||||
const uint8_t b = imageInfo.m_pMCUBufB[pixelOffset];
|
||||
gray = (r * 25 + g * 50 + b * 25) / 100;
|
||||
}
|
||||
|
||||
// Store grayscale value in MCU row buffer
|
||||
mcuRowBuffer[blockY * imageInfo.m_width + pixelX] = gray;
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
// Write all pixel rows from this MCU row to BMP file
|
||||
// Process source rows from this MCU row
|
||||
const int startRow = mcuY * mcuPixelHeight;
|
||||
const int endRow = (mcuY + 1) * mcuPixelHeight;
|
||||
|
||||
for (int y = startRow; y < endRow && y < imageInfo.m_height; y++) {
|
||||
const int bufferY = y - startRow;
|
||||
|
||||
if (!needsScaling) {
|
||||
// No scaling - direct output (1:1 mapping)
|
||||
memset(rowBuffer, 0, bytesPerRow);
|
||||
|
||||
// Pack 4 pixels per byte (2 bits each)
|
||||
for (int x = 0; x < imageInfo.m_width; x++) {
|
||||
const int bufferY = y - startRow;
|
||||
if (USE_8BIT_OUTPUT) {
|
||||
for (int x = 0; x < outWidth; x++) {
|
||||
const uint8_t gray = mcuRowBuffer[bufferY * imageInfo.m_width + x];
|
||||
const uint8_t twoBit = grayscaleTo2Bit(gray);
|
||||
|
||||
rowBuffer[x] = adjustPixel(gray);
|
||||
}
|
||||
} else {
|
||||
for (int x = 0; x < outWidth; x++) {
|
||||
const uint8_t gray = mcuRowBuffer[bufferY * imageInfo.m_width + x];
|
||||
uint8_t twoBit;
|
||||
if (atkinsonDitherer) {
|
||||
twoBit = atkinsonDitherer->processPixel(gray, x);
|
||||
} else if (fsDitherer) {
|
||||
twoBit = fsDitherer->processPixel(gray, x, fsDitherer->isReverseRow());
|
||||
} else {
|
||||
twoBit = quantize(gray, x, y);
|
||||
}
|
||||
const int byteIndex = (x * 2) / 8;
|
||||
const int bitOffset = 6 - ((x * 2) % 8); // 6, 4, 2, 0
|
||||
const int bitOffset = 6 - ((x * 2) % 8);
|
||||
rowBuffer[byteIndex] |= (twoBit << bitOffset);
|
||||
}
|
||||
|
||||
// Write row with padding
|
||||
if (atkinsonDitherer)
|
||||
atkinsonDitherer->nextRow();
|
||||
else if (fsDitherer)
|
||||
fsDitherer->nextRow();
|
||||
}
|
||||
bmpOut.write(rowBuffer, bytesPerRow);
|
||||
} else {
|
||||
// Fixed-point area averaging for exact fit scaling
|
||||
// For each output pixel X, accumulate source pixels that map to it
|
||||
// srcX range for outX: [outX * scaleX_fp >> 16, (outX+1) * scaleX_fp >> 16)
|
||||
const uint8_t* srcRow = mcuRowBuffer + bufferY * imageInfo.m_width;
|
||||
|
||||
for (int outX = 0; outX < outWidth; outX++) {
|
||||
// Calculate source X range for this output pixel
|
||||
const int srcXStart = (static_cast<uint32_t>(outX) * scaleX_fp) >> 16;
|
||||
const int srcXEnd = (static_cast<uint32_t>(outX + 1) * scaleX_fp) >> 16;
|
||||
|
||||
// Accumulate all source pixels in this range
|
||||
int sum = 0;
|
||||
int count = 0;
|
||||
for (int srcX = srcXStart; srcX < srcXEnd && srcX < imageInfo.m_width; srcX++) {
|
||||
sum += srcRow[srcX];
|
||||
count++;
|
||||
}
|
||||
|
||||
// Handle edge case: if no pixels in range, use nearest
|
||||
if (count == 0 && srcXStart < imageInfo.m_width) {
|
||||
sum = srcRow[srcXStart];
|
||||
count = 1;
|
||||
}
|
||||
|
||||
rowAccum[outX] += sum;
|
||||
rowCount[outX] += count;
|
||||
}
|
||||
|
||||
// Check if we've crossed into the next output row
|
||||
// Current source Y in fixed point: y << 16
|
||||
const uint32_t srcY_fp = static_cast<uint32_t>(y + 1) << 16;
|
||||
|
||||
// Output row when source Y crosses the boundary
|
||||
if (srcY_fp >= nextOutY_srcStart && currentOutY < outHeight) {
|
||||
memset(rowBuffer, 0, bytesPerRow);
|
||||
|
||||
if (USE_8BIT_OUTPUT) {
|
||||
for (int x = 0; x < outWidth; x++) {
|
||||
const uint8_t gray = (rowCount[x] > 0) ? (rowAccum[x] / rowCount[x]) : 0;
|
||||
rowBuffer[x] = adjustPixel(gray);
|
||||
}
|
||||
} else {
|
||||
for (int x = 0; x < outWidth; x++) {
|
||||
const uint8_t gray = (rowCount[x] > 0) ? (rowAccum[x] / rowCount[x]) : 0;
|
||||
uint8_t twoBit;
|
||||
if (atkinsonDitherer) {
|
||||
twoBit = atkinsonDitherer->processPixel(gray, x);
|
||||
} else if (fsDitherer) {
|
||||
twoBit = fsDitherer->processPixel(gray, x, fsDitherer->isReverseRow());
|
||||
} else {
|
||||
twoBit = quantize(gray, x, currentOutY);
|
||||
}
|
||||
const int byteIndex = (x * 2) / 8;
|
||||
const int bitOffset = 6 - ((x * 2) % 8);
|
||||
rowBuffer[byteIndex] |= (twoBit << bitOffset);
|
||||
}
|
||||
if (atkinsonDitherer)
|
||||
atkinsonDitherer->nextRow();
|
||||
else if (fsDitherer)
|
||||
fsDitherer->nextRow();
|
||||
}
|
||||
|
||||
bmpOut.write(rowBuffer, bytesPerRow);
|
||||
currentOutY++;
|
||||
|
||||
// Reset accumulators for next output row
|
||||
memset(rowAccum, 0, outWidth * sizeof(uint32_t));
|
||||
memset(rowCount, 0, outWidth * sizeof(uint16_t));
|
||||
|
||||
// Update boundary for next output row
|
||||
nextOutY_srcStart = static_cast<uint32_t>(currentOutY + 1) * scaleY_fp;
|
||||
}
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
// Clean up
|
||||
if (rowAccum) {
|
||||
delete[] rowAccum;
|
||||
}
|
||||
if (rowCount) {
|
||||
delete[] rowCount;
|
||||
}
|
||||
if (atkinsonDitherer) {
|
||||
delete atkinsonDitherer;
|
||||
}
|
||||
if (fsDitherer) {
|
||||
delete fsDitherer;
|
||||
}
|
||||
free(mcuRowBuffer);
|
||||
free(rowBuffer);
|
||||
|
||||
|
||||
@ -6,7 +6,7 @@ class ZipFile;
|
||||
|
||||
class JpegToBmpConverter {
|
||||
static void writeBmpHeader(Print& bmpOut, int width, int height);
|
||||
static uint8_t grayscaleTo2Bit(uint8_t grayscale);
|
||||
// [COMMENTED OUT] static uint8_t grayscaleTo2Bit(uint8_t grayscale, int x, int y);
|
||||
static unsigned char jpegReadCallback(unsigned char* pBuf, unsigned char buf_size,
|
||||
unsigned char* pBytes_actually_read, void* pCallback_data);
|
||||
|
||||
|
||||
Loading…
Reference in New Issue
Block a user