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Moved dithering functions to separate header.

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This commit is contained in:
Jonas Diemer 2026-01-09 17:47:14 +01:00
parent ec8e19ed46
commit 1cfbc6173e
1 changed files with 1 additions and 185 deletions
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186
lib/JpegToBmpConverter/JpegToBmpConverter.cpp
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@ -8,6 +8,7 @@
#include <cstring> #include <cstring>
#include "Bitmap.h" #include "Bitmap.h"
#include "Dithering.h"
// Context structure for picojpeg callback // Context structure for picojpeg callback
struct JpegReadContext { struct JpegReadContext {
@ -31,191 +32,6 @@ constexpr int TARGET_MAX_WIDTH = 480; // Max width for cover images (portrait
constexpr int TARGET_MAX_HEIGHT = 800; // Max height for cover images (portrait display height) constexpr int TARGET_MAX_HEIGHT = 800; // Max height for cover images (portrait display height)
// ============================================================================ // ============================================================================
// Atkinson dithering - distributes only 6/8 (75%) of error for cleaner results
// Error distribution pattern:
// X 1/8 1/8
// 1/8 1/8 1/8
// 1/8
// Less error buildup = fewer artifacts than Floyd-Steinberg
class AtkinsonDitherer {
public:
AtkinsonDitherer(int width) : width(width) {
errorRow0 = new int16_t[width + 4](); // Current row
errorRow1 = new int16_t[width + 4](); // Next row
errorRow2 = new int16_t[width + 4](); // Row after next
}
~AtkinsonDitherer() {
delete[] errorRow0;
delete[] errorRow1;
delete[] errorRow2;
}
uint8_t processPixel(int gray, int x) {
// 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) { inline void write16(Print& out, const uint16_t value) {
out.write(value & 0xFF); out.write(value & 0xFF);
out.write((value >> 8) & 0xFF); out.write((value >> 8) & 0xFF);