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Extended bitmap viewer by option to togglie between grayscale and bw mode

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This commit is contained in:
jpirnay
2026-04-08 09:37:08 +02:00
parent e828245c6b
commit 66508258d3
8 changed files with 198 additions and 73 deletions
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lib/Epub/Epub/converters/ImageToFramebufferDecoder.h
+5 -1
View File
@@ -60,7 +60,11 @@ struct RenderConfig {
ImageDitherMode ditherMode = ImageDitherMode::Bayer;
bool performanceMode = false;
bool useExactDimensions = false; // If true, use maxWidth/maxHeight as exact output size (no recalculation)
std::string cachePath; // If non-empty, decoder will write pixel cache to this path
// If true, the decoder uses a 1-bit Atkinson dither and emits only the values 0/3 — suitable for
// pure black-and-white display (no grayscale planes). The 4-level dither path produces values 1/2
// which the BW DirectPixelWriter collapses to black, making mid-grays render very dark.
bool monochromeOutput = false;
std::string cachePath; // If non-empty, decoder will write pixel cache to this path
};
class ImageToFramebufferDecoder {
lib/Epub/Epub/converters/JpegToFramebufferConverter.cpp
+48 -7
View File
@@ -1,8 +1,6 @@
#include "JpegToFramebufferConverter.h"
#ifdef ENABLE_IMAGE_DITHERING_EXTENSION
#include <BitmapHelpers.h>
#endif
#include <FsHelpers.h>
#include <GfxRenderer.h>
#include <HalStorage.h>
@@ -42,6 +40,11 @@ struct JpegContext {
PixelCache cache;
bool caching;
// See PngContext for the rationale: monochromeOutput requests a 1-bit Atkinson dither
// emitting only 0/3 so the BW DirectPixelWriter (`pixelValue < 3` rule) maps cleanly.
int oneBitDitherRow;
Atkinson1BitDitherer* atkinson1BitDitherer;
#ifdef ENABLE_IMAGE_DITHERING_EXTENSION
int currentDitherRow;
AtkinsonDitherer* atkinsonDitherer;
@@ -59,7 +62,9 @@ struct JpegContext {
dstHeight(0),
fineScaleFP(1 << 16),
invScaleFP(1 << 16),
caching(false)
caching(false),
oneBitDitherRow(-1),
atkinson1BitDitherer(nullptr)
#ifdef ENABLE_IMAGE_DITHERING_EXTENSION
,
currentDitherRow(-1),
@@ -69,14 +74,32 @@ struct JpegContext {
{
}
#ifdef ENABLE_IMAGE_DITHERING_EXTENSION
~JpegContext() {
delete atkinson1BitDitherer;
#ifdef ENABLE_IMAGE_DITHERING_EXTENSION
delete atkinsonDitherer;
delete diffusedBayerDitherer;
}
#endif
}
};
// Advance the 1-bit Atkinson ditherer to the requested destination row.
// Handles non-monotonic row walks (block-based JPEG decode) by reset+replay.
void prepareOneBitDitherRow(JpegContext& ctx, int dstY) {
if (!ctx.atkinson1BitDitherer) return;
if (ctx.oneBitDitherRow == -1 || dstY < ctx.oneBitDitherRow) {
ctx.atkinson1BitDitherer->reset();
ctx.oneBitDitherRow = dstY;
return;
}
while (ctx.oneBitDitherRow < dstY) {
ctx.atkinson1BitDitherer->nextRow();
ctx.oneBitDitherRow++;
}
}
#ifdef ENABLE_IMAGE_DITHERING_EXTENSION
void prepareDitherRow(JpegContext& ctx, int dstY) {
if (!ctx.config || !ctx.config->useDithering) return;
@@ -96,6 +119,10 @@ void prepareDitherRow(JpegContext& ctx, int dstY) {
}
uint8_t ditherGray(JpegContext& ctx, uint8_t gray, int localX, int outX, int outY) {
if (ctx.atkinson1BitDitherer) {
return ctx.atkinson1BitDitherer->processPixel(gray, localX) ? 3 : 0;
}
if (!ctx.config || !ctx.config->useDithering) {
return quantizeGray4Level(gray);
}
@@ -121,7 +148,9 @@ uint8_t ditherGray(JpegContext& ctx, uint8_t gray, int localX, int outX, int out
}
#else
uint8_t ditherGray(JpegContext& ctx, uint8_t gray, int localX, int outX, int outY) {
(void)ctx;
if (ctx.atkinson1BitDitherer) {
return ctx.atkinson1BitDitherer->processPixel(gray, localX) ? 3 : 0;
}
(void)localX;
return applyBayerDither4Level(gray, outX, outY);
}
@@ -254,6 +283,7 @@ int jpegDrawCallback(JPEGDRAW* pDraw) {
if (fineScaleFP == FP_ONE) {
for (int dstY = dstYStart; dstY < dstYEnd; dstY++) {
const int outY = cfgY + dstY;
prepareOneBitDitherRow(*ctx, dstY);
#ifdef ENABLE_IMAGE_DITHERING_EXTENSION
prepareDitherRow(*ctx, dstY);
#endif
@@ -285,6 +315,7 @@ int jpegDrawCallback(JPEGDRAW* pDraw) {
for (int dstY = dstYStart; dstY < dstYEnd; dstY++) {
const int outY = cfgY + dstY;
prepareOneBitDitherRow(*ctx, dstY);
#ifdef ENABLE_IMAGE_DITHERING_EXTENSION
prepareDitherRow(*ctx, dstY);
#endif
@@ -367,6 +398,7 @@ int jpegDrawCallback(JPEGDRAW* pDraw) {
// === Nearest-neighbor (downscale: fineScale < 1.0) ===
for (int dstY = dstYStart; dstY < dstYEnd; dstY++) {
const int outY = cfgY + dstY;
prepareOneBitDitherRow(*ctx, dstY);
#ifdef ENABLE_IMAGE_DITHERING_EXTENSION
prepareDitherRow(*ctx, dstY);
#endif
@@ -531,7 +563,16 @@ bool JpegToFramebufferConverter::decodeToFramebuffer(const std::string& imagePat
}
}
if (config.useDithering) {
// See PngToFramebufferConverter for rationale: BW-only display needs a 1-bit
// dither so mid-grays don't collapse to black under DirectPixelWriter's `< 3` rule.
if (config.monochromeOutput) {
ctx.atkinson1BitDitherer = new (std::nothrow) Atkinson1BitDitherer(destWidth);
if (!ctx.atkinson1BitDitherer) {
LOG_ERR("JPG", "Failed to allocate 1-bit Atkinson ditherer, falling back to 4-level dither");
}
}
if (config.useDithering && !ctx.atkinson1BitDitherer) {
#ifdef ENABLE_IMAGE_DITHERING_EXTENSION
switch (config.ditherMode) {
case ImageDitherMode::Atkinson:
lib/Epub/Epub/converters/PngToFramebufferConverter.cpp
+12 -18
View File
@@ -38,12 +38,11 @@ struct PngContext {
uint8_t* grayLineBuffer;
// When the renderer is in BW mode the framebuffer is 1 bpp and the
// DirectPixelWriter collapses any value < 3 to black. The 4-level dither
// path therefore turns mid-grays into solid black. In that case we run a
// proper 1-bit Atkinson dither (matching PngToBmpConverter's BW path) and
// emit only values 0 or 3, which round-trip cleanly through the BW writer.
bool renderModeIsBW;
// When the caller requests monochrome output (RenderConfig::monochromeOutput),
// we run a proper 1-bit Atkinson dither (matching PngToBmpConverter's BW path)
// and emit only values 0 or 3, which round-trip cleanly through the BW writer's
// `pixelValue < 3` rule. The 4-level dither path collapses mid-grays to solid
// black under that rule.
int oneBitDitherRow;
Atkinson1BitDitherer* atkinson1BitDitherer;
@@ -66,7 +65,6 @@ struct PngContext {
lastDstY(-1),
caching(false),
grayLineBuffer(nullptr),
renderModeIsBW(false),
oneBitDitherRow(-1),
atkinson1BitDitherer(nullptr)
#ifdef ENABLE_IMAGE_DITHERING_EXTENSION
@@ -494,17 +492,13 @@ bool PngToFramebufferConverter::decodeToFramebuffer(const std::string& imagePath
}
}
// When the renderer is in BW mode, use a 1-bit Atkinson ditherer instead of
// the 4-level paths below. The 4-level dither produces values 1-2 for mid
// grays, which DirectPixelWriter then collapses to black under its `< 3`
// BW rule, making images render very dark. The 1-bit ditherer emits only
// 0 or 3 so the BW writer maps cleanly to black/white. Caching still uses
// the 2-bit cache file format, but caching is disabled in this path
// (BmpViewerActivity passes an empty cachePath).
ctx.renderModeIsBW = (renderer.getRenderMode() == GfxRenderer::BW);
LOG_DBG("PNG", "Render mode at decode: %d (BW=%d) -> 1bit dither=%d", (int)renderer.getRenderMode(),
(int)GfxRenderer::BW, ctx.renderModeIsBW ? 1 : 0);
if (ctx.renderModeIsBW) {
// When the caller explicitly requests monochrome output, use a 1-bit Atkinson
// ditherer instead of the 4-level paths below. The 4-level dither produces
// values 1-2 for mid grays, which DirectPixelWriter then collapses to black
// under its `< 3` BW rule, making images render very dark in BW-only mode.
// The 1-bit ditherer emits only 0 or 3 so the BW writer maps cleanly to
// black/white.
if (config.monochromeOutput) {
ctx.atkinson1BitDitherer = new (std::nothrow) Atkinson1BitDitherer(ctx.dstWidth);
if (!ctx.atkinson1BitDitherer) {
LOG_ERR("PNG", "Failed to allocate 1-bit Atkinson ditherer, falling back to 4-level dither");