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Move helper functions to Bitmap

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This commit is contained in:
Jonas Diemer 2026-01-09 17:36:30 +01:00
parent 54e5388e76
commit 40a92f3d34
3 changed files with 48 additions and 93 deletions
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47
lib/GfxRenderer/Bitmap.cpp
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@ -8,15 +8,22 @@
// ============================================================================
// Note: For cover images, dithering is done in JpegToBmpConverter.cpp
// This file handles BMP reading - use simple quantization to avoid double-dithering
// constexpr bool USE_FLOYD_STEINBERG = true; // Disabled - dithering done at JPEG conversion
constexpr bool USE_NOISE_DITHERING = false; // Hash-based noise dithering
constexpr bool GAMMA_CORRECTION = true; // Gamma curve, only if USE_BRIGHTNESS=true
// Brightness/Contrast adjustments:
constexpr bool USE_BRIGHTNESS = false; // true: apply brightness/gamma adjustments
constexpr int BRIGHTNESS_BOOST = 10; // Brightness offset (0-50)
constexpr bool GAMMA_CORRECTION = false; // Gamma curve (brightens midtones)
constexpr float CONTRAST_FACTOR = 1.15f; // Contrast multiplier (1.0 = no change, >1 = more contrast)
// ============================================================================
// Integer approximation of gamma correction (brightens midtones)
// Uses a simple curve: out = 255 * sqrt(in/255) ≈ sqrt(in * 255)
static inline int applyGamma(int gray) {
if (!GAMMA_CORRECTION) return gray;
// Fast integer square root approximation for gamma ~0.5 (brightening)
// This brightens dark/mid tones while preserving highlights
const int product = gray * 255;
// Newton-Raphson integer sqrt (2 iterations for good accuracy)
int x = gray;
if (x > 0) {
x = (x + product / x) >> 1;
@ -25,6 +32,7 @@ static inline int applyGamma(int gray) {
return x > 255 ? 255 : x;
}
// TODO: remove
static inline uint8_t boostBrightness(int gray, uint8_t boost) {
if (boost > 0) {
gray += boost;
@ -33,10 +41,34 @@ static inline uint8_t boostBrightness(int gray, uint8_t boost) {
}
return gray;
}
// Simple quantization without dithering - just divide into 4 levels
static inline uint8_t quantizeSimple(int gray) {
// return static_cast<uint8_t>(gray >> 6);
// Apply contrast adjustment around midpoint (128)
// factor > 1.0 increases contrast, < 1.0 decreases
static inline int applyContrast(int gray) {
// Integer-based contrast: (gray - 128) * factor + 128
// Using fixed-point: factor 1.15 ≈ 115/100
constexpr int factorNum = static_cast<int>(CONTRAST_FACTOR * 100);
int adjusted = ((gray - 128) * factorNum) / 100 + 128;
if (adjusted < 0) adjusted = 0;
if (adjusted > 255) adjusted = 255;
return adjusted;
}
// Combined brightness/contrast/gamma adjustment
int adjustPixel(int gray) {
if (!USE_BRIGHTNESS) return gray;
// Order: contrast first, then brightness, then gamma
gray = applyContrast(gray);
gray += BRIGHTNESS_BOOST;
if (gray > 255) gray = 255;
if (gray < 0) gray = 0;
gray = applyGamma(gray);
return gray;
}
// Simple quantization without dithering - divide into 4 levels
// The thresholds are fine-tuned to the X4 display
uint8_t quantizeSimple(int gray) {
if (gray < 50) {
return 0;
} else if (gray < 70) {
@ -49,6 +81,7 @@ static inline uint8_t quantizeSimple(int gray) {
}
// Hash-based noise dithering - survives downsampling without moiré artifacts
// Uses integer hash to generate pseudo-random threshold per pixel
static inline uint8_t quantizeNoise(int gray, int x, int y) {
uint32_t hash = static_cast<uint32_t>(x) * 374761393u + static_cast<uint32_t>(y) * 668265263u;
hash = (hash ^ (hash >> 13)) * 1274126177u;
@ -64,8 +97,8 @@ static inline uint8_t quantizeNoise(int gray, int x, int y) {
}
}
// Main quantization function
static inline uint8_t quantize(int gray, int x, int y) {
// Main quantization function - selects between methods based on config
uint8_t quantize(int gray, int x, int y) {
if (USE_NOISE_DITHERING) {
return quantizeNoise(gray, x, y);
} else {

5
lib/GfxRenderer/Bitmap.h
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@ -62,3 +62,8 @@ class Bitmap {
mutable int16_t* errorNextRow = nullptr;
mutable int prevRowY = -1; // Track row progression for error propagation
};
// Helper functions
uint8_t quantize(int gray, int x, int y);
uint8_t quantizeSimple(int gray);
int adjustPixel(int gray);

89
lib/JpegToBmpConverter/JpegToBmpConverter.cpp
View File

@ -7,6 +7,8 @@
#include <cstdio>
#include <cstring>
#include "Bitmap.h"
// Context structure for picojpeg callback
struct JpegReadContext {
FsFile& file;
@ -23,97 +25,12 @@ constexpr bool USE_8BIT_OUTPUT = false; // true: 8-bit grayscale (no quantizati
constexpr bool USE_ATKINSON = true; // Atkinson dithering (cleaner than F-S, less error diffusion)
constexpr bool USE_FLOYD_STEINBERG = false; // Floyd-Steinberg error diffusion (can cause "worm" artifacts)
constexpr bool USE_NOISE_DITHERING = false; // Hash-based noise dithering (good for downsampling)
// Brightness/Contrast adjustments:
constexpr bool USE_BRIGHTNESS = false; // true: apply brightness/gamma adjustments
constexpr int BRIGHTNESS_BOOST = 10; // Brightness offset (0-50)
constexpr bool GAMMA_CORRECTION = false; // Gamma curve (brightens midtones)
constexpr float CONTRAST_FACTOR = 1.15f; // Contrast multiplier (1.0 = no change, >1 = more contrast)
// Pre-resize to target display size (CRITICAL: avoids dithering artifacts from post-downsampling)
constexpr bool USE_PRESCALE = true; // true: scale image to target size before dithering
constexpr int TARGET_MAX_WIDTH = 480; // Max width for cover images (portrait display width)
constexpr int TARGET_MAX_HEIGHT = 800; // Max height for cover images (portrait display height)
// ============================================================================
// Integer approximation of gamma correction (brightens midtones)
// Uses a simple curve: out = 255 * sqrt(in/255) ≈ sqrt(in * 255)
static inline int applyGamma(int gray) {
if (!GAMMA_CORRECTION) return gray;
// Fast integer square root approximation for gamma ~0.5 (brightening)
// This brightens dark/mid tones while preserving highlights
const int product = gray * 255;
// Newton-Raphson integer sqrt (2 iterations for good accuracy)
int x = gray;
if (x > 0) {
x = (x + product / x) >> 1;
x = (x + product / x) >> 1;
}
return x > 255 ? 255 : x;
}
// Apply contrast adjustment around midpoint (128)
// factor > 1.0 increases contrast, < 1.0 decreases
static inline int applyContrast(int gray) {
// Integer-based contrast: (gray - 128) * factor + 128
// Using fixed-point: factor 1.15 ≈ 115/100
constexpr int factorNum = static_cast<int>(CONTRAST_FACTOR * 100);
int adjusted = ((gray - 128) * factorNum) / 100 + 128;
if (adjusted < 0) adjusted = 0;
if (adjusted > 255) adjusted = 255;
return adjusted;
}
// Combined brightness/contrast/gamma adjustment
static inline int adjustPixel(int gray) {
if (!USE_BRIGHTNESS) return gray;
// Order: contrast first, then brightness, then gamma
gray = applyContrast(gray);
gray += BRIGHTNESS_BOOST;
if (gray > 255) gray = 255;
if (gray < 0) gray = 0;
gray = applyGamma(gray);
return gray;
}
// Simple quantization without dithering - just divide into 4 levels
static inline uint8_t quantizeSimple(int gray) {
gray = adjustPixel(gray);
// Simple 2-bit quantization: 0-63=0, 64-127=1, 128-191=2, 192-255=3
return static_cast<uint8_t>(gray >> 6);
}
// Hash-based noise dithering - survives downsampling without moiré artifacts
// Uses integer hash to generate pseudo-random threshold per pixel
static inline uint8_t quantizeNoise(int gray, int x, int y) {
gray = adjustPixel(gray);
// Generate noise threshold using integer hash (no regular pattern to alias)
uint32_t hash = static_cast<uint32_t>(x) * 374761393u + static_cast<uint32_t>(y) * 668265263u;
hash = (hash ^ (hash >> 13)) * 1274126177u;
const int threshold = static_cast<int>(hash >> 24); // 0-255
// Map gray (0-255) to 4 levels with dithering
const int scaled = gray * 3;
if (scaled < 255) {
return (scaled + threshold >= 255) ? 1 : 0;
} else if (scaled < 510) {
return ((scaled - 255) + threshold >= 255) ? 2 : 1;
} else {
return ((scaled - 510) + threshold >= 255) ? 3 : 2;
}
}
// Main quantization function - selects between methods based on config
static inline uint8_t quantize(int gray, int x, int y) {
if (USE_NOISE_DITHERING) {
return quantizeNoise(gray, x, y);
} else {
return quantizeSimple(gray);
}
}
// Atkinson dithering - distributes only 6/8 (75%) of error for cleaner results
// Error distribution pattern:
// X 1/8 1/8
@ -686,7 +603,7 @@ bool JpegToBmpConverter::jpegFileToBmpStream(FsFile& jpegFile, Print& bmpOut) {
}
} else {
for (int x = 0; x < outWidth; x++) {
const uint8_t gray = (rowCount[x] > 0) ? (rowAccum[x] / rowCount[x]) : 0;
const uint8_t gray = adjustPixel((rowCount[x] > 0) ? (rowAccum[x] / rowCount[x]) : 0);
uint8_t twoBit;
if (atkinsonDitherer) {
twoBit = atkinsonDitherer->processPixel(gray, x);