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Add dithering algorithms

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This commit is contained in:
jpirnay
2026-04-06 13:00:27 +02:00
parent f45b780900
commit eb95cacad4
10 changed files with 335 additions and 59 deletions
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lib/Epub/Epub/converters/JpegToFramebufferConverter.cpp
+85 -37
View File
@@ -1,5 +1,6 @@
#include "JpegToFramebufferConverter.h"
#include <BitmapHelpers.h>
#include <FsHelpers.h>
#include <GfxRenderer.h>
#include <HalStorage.h>
@@ -39,6 +40,10 @@ struct JpegContext {
PixelCache cache;
bool caching;
int currentDitherRow;
AtkinsonDitherer* atkinsonDitherer;
DiffusedBayerDitherer* diffusedBayerDitherer;
JpegContext()
: renderer(nullptr),
config(nullptr),
@@ -50,9 +55,59 @@ struct JpegContext {
dstHeight(0),
fineScaleFP(1 << 16),
invScaleFP(1 << 16),
caching(false) {}
caching(false),
currentDitherRow(-1),
atkinsonDitherer(nullptr),
diffusedBayerDitherer(nullptr) {}
~JpegContext() {
delete atkinsonDitherer;
delete diffusedBayerDitherer;
}
};
void prepareDitherRow(JpegContext& ctx, int dstY) {
if (!ctx.config || !ctx.config->useDithering) return;
if (ctx.currentDitherRow == -1 || dstY < ctx.currentDitherRow) {
if (ctx.atkinsonDitherer) ctx.atkinsonDitherer->reset();
if (ctx.diffusedBayerDitherer) ctx.diffusedBayerDitherer->reset();
ctx.currentDitherRow = dstY;
return;
}
while (ctx.currentDitherRow < dstY) {
if (ctx.atkinsonDitherer) ctx.atkinsonDitherer->nextRow();
if (ctx.diffusedBayerDitherer) ctx.diffusedBayerDitherer->nextRow();
ctx.currentDitherRow++;
}
}
uint8_t ditherGray(JpegContext& ctx, uint8_t gray, int localX, int outX, int outY) {
if (!ctx.config || !ctx.config->useDithering) {
return quantizeGray4Level(gray);
}
switch (ctx.config->ditherMode) {
case ImageDitherMode::Atkinson:
if (ctx.atkinsonDitherer) {
return ctx.atkinsonDitherer->processPixel(gray, localX);
}
break;
case ImageDitherMode::DiffusedBayer:
if (ctx.diffusedBayerDitherer) {
return ctx.diffusedBayerDitherer->processPixel(gray, localX, outX, outY);
}
break;
case ImageDitherMode::Bayer:
case ImageDitherMode::COUNT:
default:
break;
}
return applyBayerDither4Level(gray, outX, outY);
}
// File I/O callbacks use pFile->fHandle to access the FsFile*,
// avoiding the need for global file state.
void* jpegOpen(const char* filename, int32_t* size) {
@@ -136,7 +191,6 @@ int jpegDrawCallback(JPEGDRAW* pDraw) {
if (stride <= 0 || blockH <= 0 || validW <= 0) return 1;
const bool useDithering = ctx->config->useDithering;
const bool caching = ctx->caching;
const int32_t fineScaleFP = ctx->fineScaleFP;
const int32_t invScaleFP = ctx->invScaleFP;
@@ -181,19 +235,14 @@ int jpegDrawCallback(JPEGDRAW* pDraw) {
if (fineScaleFP == FP_ONE) {
for (int dstY = dstYStart; dstY < dstYEnd; dstY++) {
const int outY = cfgY + dstY;
prepareDitherRow(*ctx, dstY);
pw.beginRow(outY);
if (caching) cw.beginRow(outY, ctx->config->y);
const uint8_t* row = &pixels[(dstY - blockY) * stride];
for (int dstX = dstXStart; dstX < dstXEnd; dstX++) {
const int outX = cfgX + dstX;
uint8_t gray = row[dstX - blockX];
uint8_t dithered;
if (useDithering) {
dithered = applyBayerDither4Level(gray, outX, outY);
} else {
dithered = gray / 85;
if (dithered > 3) dithered = 3;
}
uint8_t dithered = ditherGray(*ctx, gray, dstX, outX, outY);
pw.writePixel(outX, dithered);
if (caching) cw.writePixel(outX, dithered);
}
@@ -215,6 +264,7 @@ int jpegDrawCallback(JPEGDRAW* pDraw) {
for (int dstY = dstYStart; dstY < dstYEnd; dstY++) {
const int outY = cfgY + dstY;
prepareDitherRow(*ctx, dstY);
pw.beginRow(outY);
if (caching) cw.beginRow(outY, ctx->config->y);
const int32_t srcFyFP = dstY * invScaleFP;
@@ -246,13 +296,7 @@ int jpegDrawCallback(JPEGDRAW* pDraw) {
int bot = ((int)row1[lx0] * fxInv + (int)row1[lx1] * fx) >> FP_SHIFT;
uint8_t gray = (uint8_t)((top * fyInv + bot * fy) >> FP_SHIFT);
uint8_t dithered;
if (useDithering) {
dithered = applyBayerDither4Level(gray, outX, outY);
} else {
dithered = gray / 85;
if (dithered > 3) dithered = 3;
}
uint8_t dithered = ditherGray(*ctx, gray, dstX, outX, outY);
pw.writePixel(outX, dithered);
if (caching) cw.writePixel(outX, dithered);
}
@@ -269,13 +313,7 @@ int jpegDrawCallback(JPEGDRAW* pDraw) {
int bot = ((int)row1[lx0] * fxInv + (int)row1[lx0 + 1] * fx) >> FP_SHIFT;
uint8_t gray = (uint8_t)((top * fyInv + bot * fy) >> FP_SHIFT);
uint8_t dithered;
if (useDithering) {
dithered = applyBayerDither4Level(gray, outX, outY);
} else {
dithered = gray / 85;
if (dithered > 3) dithered = 3;
}
uint8_t dithered = ditherGray(*ctx, gray, dstX, outX, outY);
pw.writePixel(outX, dithered);
if (caching) cw.writePixel(outX, dithered);
}
@@ -295,13 +333,7 @@ int jpegDrawCallback(JPEGDRAW* pDraw) {
int bot = ((int)row1[lx0] * fxInv + (int)row1[lx1] * fx) >> FP_SHIFT;
uint8_t gray = (uint8_t)((top * fyInv + bot * fy) >> FP_SHIFT);
uint8_t dithered;
if (useDithering) {
dithered = applyBayerDither4Level(gray, outX, outY);
} else {
dithered = gray / 85;
if (dithered > 3) dithered = 3;
}
uint8_t dithered = ditherGray(*ctx, gray, dstX, outX, outY);
pw.writePixel(outX, dithered);
if (caching) cw.writePixel(outX, dithered);
}
@@ -312,6 +344,7 @@ int jpegDrawCallback(JPEGDRAW* pDraw) {
// === Nearest-neighbor (downscale: fineScale < 1.0) ===
for (int dstY = dstYStart; dstY < dstYEnd; dstY++) {
const int outY = cfgY + dstY;
prepareDitherRow(*ctx, dstY);
pw.beginRow(outY);
if (caching) cw.beginRow(outY, ctx->config->y);
const int32_t srcFyFP = dstY * invScaleFP;
@@ -328,13 +361,7 @@ int jpegDrawCallback(JPEGDRAW* pDraw) {
if (lx >= validW) lx = validW - 1;
uint8_t gray = row[lx];
uint8_t dithered;
if (useDithering) {
dithered = applyBayerDither4Level(gray, outX, outY);
} else {
dithered = gray / 85;
if (dithered > 3) dithered = 3;
}
uint8_t dithered = ditherGray(*ctx, gray, dstX, outX, outY);
pw.writePixel(outX, dithered);
if (caching) cw.writePixel(outX, dithered);
}
@@ -479,6 +506,27 @@ bool JpegToFramebufferConverter::decodeToFramebuffer(const std::string& imagePat
}
}
if (config.useDithering) {
switch (config.ditherMode) {
case ImageDitherMode::Atkinson:
ctx.atkinsonDitherer = new (std::nothrow) AtkinsonDitherer(destWidth);
if (!ctx.atkinsonDitherer) {
LOG_ERR("JPG", "Failed to allocate Atkinson ditherer, falling back to Bayer");
}
break;
case ImageDitherMode::DiffusedBayer:
ctx.diffusedBayerDitherer = new (std::nothrow) DiffusedBayerDitherer(destWidth);
if (!ctx.diffusedBayerDitherer) {
LOG_ERR("JPG", "Failed to allocate diffused Bayer ditherer, falling back to Bayer");
}
break;
case ImageDitherMode::Bayer:
case ImageDitherMode::COUNT:
default:
break;
}
}
unsigned long decodeStart = millis();
rc = jpeg->decode(0, 0, jpegScaleOption);
unsigned long decodeTime = millis() - decodeStart;