fix: Align double FAST_REFRESH image rendering with upstream PR #957

Reorder refresh branches so image+AA pages always use the double
FAST_REFRESH technique instead of occasionally falling through to
HALF_REFRESH when the refresh counter expires. Image pages no longer
count toward the full refresh cadence. Remove experimental Method B
toggle (USE_IMAGE_DOUBLE_FAST_REFRESH / displayWindow).

Co-authored-by: Cursor <cursoragent@cursor.com>

lib/Epub/Epub/converters/PngToFramebufferConverter.cpp

@@ -90,6 +90,32 @@ int32_t pngSeekWithHandle(PNGFILE* pFile, int32_t pos) {
 constexpr size_t PNG_DECODER_APPROX_SIZE = 44 * 1024;                          // ~42 KB + overhead
 constexpr size_t MIN_FREE_HEAP_FOR_PNG = PNG_DECODER_APPROX_SIZE + 16 * 1024;  // decoder + 16 KB headroom
 
+// PNGdec keeps TWO scanlines in its internal ucPixels buffer (current + previous)
+// and each scanline includes a leading filter byte.
+// Required storage is therefore approximately: 2 * (pitch + 1) + alignment slack.
+// If PNG_MAX_BUFFERED_PIXELS is smaller than this requirement for a given image,
+// PNGdec can overrun its internal buffer before our draw callback executes.
+int bytesPerPixelFromType(int pixelType) {
+  switch (pixelType) {
+    case PNG_PIXEL_TRUECOLOR:
+      return 3;
+    case PNG_PIXEL_GRAY_ALPHA:
+      return 2;
+    case PNG_PIXEL_TRUECOLOR_ALPHA:
+      return 4;
+    case PNG_PIXEL_GRAYSCALE:
+    case PNG_PIXEL_INDEXED:
+    default:
+      return 1;
+  }
+}
+
+int requiredPngInternalBufferBytes(int srcWidth, int pixelType) {
+  // +1 filter byte per scanline, *2 for current+previous lines, +32 for alignment margin.
+  int pitch = srcWidth * bytesPerPixelFromType(pixelType);
+  return ((pitch + 1) * 2) + 32;
+}
+
 // Convert entire source line to grayscale with alpha blending to white background.
 // For indexed PNGs with tRNS chunk, alpha values are stored at palette[768] onwards.
 // Processing the whole line at once improves cache locality and reduces per-pixel overhead.
@@ -304,6 +330,18 @@ bool PngToFramebufferConverter::decodeToFramebuffer(const std::string& imagePath
   LOG_DBG("PNG", "PNG %dx%d -> %dx%d (scale %.2f), bpp: %d", ctx.srcWidth, ctx.srcHeight, ctx.dstWidth, ctx.dstHeight,
           ctx.scale, png->getBpp());
 
+  const int pixelType = png->getPixelType();
+  const int requiredInternal = requiredPngInternalBufferBytes(ctx.srcWidth, pixelType);
+  if (requiredInternal > PNG_MAX_BUFFERED_PIXELS) {
+    LOG_ERR("PNG",
+            "PNG row buffer too small: need %d bytes for width=%d type=%d, configured PNG_MAX_BUFFERED_PIXELS=%d",
+            requiredInternal, ctx.srcWidth, pixelType, PNG_MAX_BUFFERED_PIXELS);
+    LOG_ERR("PNG", "Aborting decode to avoid PNGdec internal buffer overflow");
+    png->close();
+    delete png;
+    return false;
+  }
+
   if (png->getBpp() != 8) {
     warnUnsupportedFeature("bit depth (" + std::to_string(png->getBpp()) + "bpp)", imagePath);
   }

lib/Epub/Epub/css/CssParser.cpp

@@ -295,6 +295,9 @@ void CssParser::parseDeclarationIntoStyle(const std::string& decl, CssStyle& sty
       style.defined.paddingTop = style.defined.paddingRight = style.defined.paddingBottom = style.defined.paddingLeft =
           1;
     }
+  } else if (propNameBuf == "height") {
+    style.imageHeight = interpretLength(propValueBuf);
+    style.defined.imageHeight = 1;
   } else if (propNameBuf == "width") {
     style.width = interpretLength(propValueBuf);
     style.defined.width = 1;
@@ -565,7 +568,7 @@ CssStyle CssParser::parseInlineStyle(const std::string& styleValue) { return par
 // Cache serialization
 
 // Cache format version - increment when format changes
-constexpr uint8_t CSS_CACHE_VERSION = 2;
+constexpr uint8_t CSS_CACHE_VERSION = 3;
 constexpr char rulesCache[] = "/css_rules.cache";
 
 bool CssParser::hasCache() const { return Storage.exists((cachePath + rulesCache).c_str()); }
@@ -616,6 +619,8 @@ bool CssParser::saveToCache() const {
     writeLength(style.paddingBottom);
     writeLength(style.paddingLeft);
     writeLength(style.paddingRight);
+    writeLength(style.imageHeight);
+    writeLength(style.width);
 
     // Write defined flags as uint16_t
     uint16_t definedBits = 0;
@@ -632,6 +637,8 @@ bool CssParser::saveToCache() const {
     if (style.defined.paddingBottom) definedBits |= 1 << 10;
     if (style.defined.paddingLeft) definedBits |= 1 << 11;
     if (style.defined.paddingRight) definedBits |= 1 << 12;
+    if (style.defined.width) definedBits |= 1 << 13;
+    if (style.defined.imageHeight) definedBits |= 1 << 14;
     file.write(reinterpret_cast<const uint8_t*>(&definedBits), sizeof(definedBits));
   }
 
@@ -733,7 +740,8 @@ bool CssParser::loadFromCache() {
 
     if (!readLength(style.textIndent) || !readLength(style.marginTop) || !readLength(style.marginBottom) ||
         !readLength(style.marginLeft) || !readLength(style.marginRight) || !readLength(style.paddingTop) ||
-        !readLength(style.paddingBottom) || !readLength(style.paddingLeft) || !readLength(style.paddingRight)) {
+        !readLength(style.paddingBottom) || !readLength(style.paddingLeft) || !readLength(style.paddingRight) ||
+        !readLength(style.imageHeight) || !readLength(style.width)) {
       rulesBySelector_.clear();
       file.close();
       return false;
@@ -759,6 +767,8 @@ bool CssParser::loadFromCache() {
     style.defined.paddingBottom = (definedBits & 1 << 10) != 0;
     style.defined.paddingLeft = (definedBits & 1 << 11) != 0;
     style.defined.paddingRight = (definedBits & 1 << 12) != 0;
+    style.defined.width = (definedBits & 1 << 13) != 0;
+    style.defined.imageHeight = (definedBits & 1 << 14) != 0;
 
     rulesBySelector_[selector] = style;
   }

lib/Epub/Epub/css/CssStyle.h

@@ -70,6 +70,7 @@ struct CssPropertyFlags {
   uint16_t paddingLeft : 1;
   uint16_t paddingRight : 1;
   uint16_t width : 1;
+  uint16_t imageHeight : 1;
 
   CssPropertyFlags()
       : textAlign(0),
@@ -85,18 +86,20 @@ struct CssPropertyFlags {
         paddingBottom(0),
         paddingLeft(0),
         paddingRight(0),
-        width(0) {}
+        width(0),
+        imageHeight(0) {}
 
   [[nodiscard]] bool anySet() const {
     return textAlign || fontStyle || fontWeight || textDecoration || textIndent || marginTop || marginBottom ||
-           marginLeft || marginRight || paddingTop || paddingBottom || paddingLeft || paddingRight || width;
+           marginLeft || marginRight || paddingTop || paddingBottom || paddingLeft || paddingRight || width ||
+           imageHeight;
   }
 
   void clearAll() {
     textAlign = fontStyle = fontWeight = textDecoration = textIndent = 0;
     marginTop = marginBottom = marginLeft = marginRight = 0;
     paddingTop = paddingBottom = paddingLeft = paddingRight = 0;
-    width = 0;
+    width = imageHeight = 0;
   }
 };
 
@@ -118,7 +121,8 @@ struct CssStyle {
   CssLength paddingBottom;  // Padding after
   CssLength paddingLeft;    // Padding left
   CssLength paddingRight;   // Padding right
-  CssLength width;          // Element width (used for table columns/cells)
+  CssLength width;          // Element width (used for table columns/cells and image sizing)
+  CssLength imageHeight;    // Height for img (e.g. 2em) -- width derived from aspect ratio when only height set
 
   CssPropertyFlags defined;  // Tracks which properties were explicitly set
 
@@ -181,6 +185,10 @@ struct CssStyle {
       width = base.width;
       defined.width = 1;
     }
+    if (base.hasImageHeight()) {
+      imageHeight = base.imageHeight;
+      defined.imageHeight = 1;
+    }
   }
 
   [[nodiscard]] bool hasTextAlign() const { return defined.textAlign; }
@@ -197,6 +205,7 @@ struct CssStyle {
   [[nodiscard]] bool hasPaddingLeft() const { return defined.paddingLeft; }
   [[nodiscard]] bool hasPaddingRight() const { return defined.paddingRight; }
   [[nodiscard]] bool hasWidth() const { return defined.width; }
+  [[nodiscard]] bool hasImageHeight() const { return defined.imageHeight; }
 
   void reset() {
     textAlign = CssTextAlign::Left;
@@ -207,6 +216,7 @@ struct CssStyle {
     marginTop = marginBottom = marginLeft = marginRight = CssLength{};
     paddingTop = paddingBottom = paddingLeft = paddingRight = CssLength{};
     width = CssLength{};
+    imageHeight = CssLength{};
     defined.clearAll();
   }
 };

lib/Epub/Epub/parsers/ChapterHtmlSlimParser.cpp

@@ -418,7 +418,47 @@ void XMLCALL ChapterHtmlSlimParser::startElement(void* userData, const XML_Char*
               if (decoder->getDimensions(cachedImagePath, dims)) {
                 LOG_DBG("EHP", "Image dimensions: %dx%d", dims.width, dims.height);
 
-                // Scale to fit viewport while maintaining aspect ratio
+                int displayWidth = 0;
+                int displayHeight = 0;
+                const float emSize =
+                    static_cast<float>(self->renderer.getLineHeight(self->fontId)) * self->lineCompression;
+                CssStyle imgStyle = self->cssParser ? self->cssParser->resolveStyle("img", classAttr) : CssStyle{};
+                if (!styleAttr.empty()) {
+                  imgStyle.applyOver(CssParser::parseInlineStyle(styleAttr));
+                }
+                const bool hasCssHeight = imgStyle.hasImageHeight();
+                const bool hasCssWidth = imgStyle.hasWidth();
+
+                if (hasCssHeight && dims.width > 0 && dims.height > 0) {
+                  displayHeight = static_cast<int>(
+                      imgStyle.imageHeight.toPixels(emSize, static_cast<float>(self->viewportHeight)) + 0.5f);
+                  if (displayHeight < 1) displayHeight = 1;
+                  displayWidth =
+                      static_cast<int>(displayHeight * (static_cast<float>(dims.width) / dims.height) + 0.5f);
+                  if (displayWidth > self->viewportWidth) {
+                    displayWidth = self->viewportWidth;
+                    displayHeight =
+                        static_cast<int>(displayWidth * (static_cast<float>(dims.height) / dims.width) + 0.5f);
+                    if (displayHeight < 1) displayHeight = 1;
+                  }
+                  if (displayWidth < 1) displayWidth = 1;
+                  LOG_DBG("EHP", "Display size from CSS height: %dx%d", displayWidth, displayHeight);
+                } else if (hasCssWidth && !hasCssHeight && dims.width > 0 && dims.height > 0) {
+                  displayWidth = static_cast<int>(
+                      imgStyle.width.toPixels(emSize, static_cast<float>(self->viewportWidth)) + 0.5f);
+                  if (displayWidth > self->viewportWidth) displayWidth = self->viewportWidth;
+                  if (displayWidth < 1) displayWidth = 1;
+                  displayHeight =
+                      static_cast<int>(displayWidth * (static_cast<float>(dims.height) / dims.width) + 0.5f);
+                  if (displayHeight > self->viewportHeight) {
+                    displayHeight = self->viewportHeight;
+                    displayWidth =
+                        static_cast<int>(displayHeight * (static_cast<float>(dims.width) / dims.height) + 0.5f);
+                    if (displayWidth < 1) displayWidth = 1;
+                  }
+                  if (displayHeight < 1) displayHeight = 1;
+                  LOG_DBG("EHP", "Display size from CSS width: %dx%d", displayWidth, displayHeight);
+                } else {
                   int maxWidth = self->viewportWidth;
                   int maxHeight = self->viewportHeight;
                   float scaleX = (dims.width > maxWidth) ? (float)maxWidth / dims.width : 1.0f;
@@ -426,10 +466,10 @@ void XMLCALL ChapterHtmlSlimParser::startElement(void* userData, const XML_Char*
                   float scale = (scaleX < scaleY) ? scaleX : scaleY;
                   if (scale > 1.0f) scale = 1.0f;
 
-                int displayWidth = (int)(dims.width * scale);
-                int displayHeight = (int)(dims.height * scale);
-
+                  displayWidth = (int)(dims.width * scale);
+                  displayHeight = (int)(dims.height * scale);
                   LOG_DBG("EHP", "Display size: %dx%d (scale %.2f)", displayWidth, displayHeight, scale);
+                }
 
                 // Create page for image - only break if image won't fit remaining space
                 if (self->currentPage && !self->currentPage->elements.empty() &&

lib/GfxRenderer/GfxRenderer.cpp

@@ -824,7 +824,8 @@ int GfxRenderer::getSpaceWidth(const int fontId, const EpdFontFamily::Style styl
     return 0;
   }
 
-  return fontIt->second.getGlyph(' ', style)->advanceX;
+  const EpdGlyph* spaceGlyph = fontIt->second.getGlyph(' ', style);
+  return spaceGlyph ? spaceGlyph->advanceX : 0;
 }
 
 int GfxRenderer::getTextAdvanceX(const int fontId, const char* text, const EpdFontFamily::Style style) const {
@@ -838,7 +839,9 @@ int GfxRenderer::getTextAdvanceX(const int fontId, const char* text, const EpdFo
   int width = 0;
   const auto& font = fontIt->second;
   while ((cp = utf8NextCodepoint(reinterpret_cast<const uint8_t**>(&text)))) {
-    width += font.getGlyph(cp, style)->advanceX;
+    const EpdGlyph* glyph = font.getGlyph(cp, style);
+    if (!glyph) glyph = font.getGlyph(REPLACEMENT_GLYPH, style);
+    if (glyph) width += glyph->advanceX;
   }
   return width;
 }

platformio.ini

@@ -2,7 +2,7 @@
 default_envs = default
 
 [crosspoint]
-version = 1.0.0
+version = 1.1.1-rc
 
 [base]
 platform = espressif32 @ 6.12.0
@@ -31,9 +31,9 @@ build_flags =
   -std=gnu++2a
 # Enable UTF-8 long file names in SdFat
   -DUSE_UTF8_LONG_NAMES=1
-# Increase PNG scanline buffer to support up to 800px wide images
+# Increase PNG scanline buffer to support up to 2048px wide images
 # Default is (320*4+1)*2=2562, we need more for larger images
-  -DPNG_MAX_BUFFERED_PIXELS=6402
+  -DPNG_MAX_BUFFERED_PIXELS=16416
 
 build_unflags =
   -std=gnu++11

src/activities/boot_sleep/SleepActivity.cpp

@@ -21,6 +21,11 @@
 #include "util/BookSettings.h"
 #include "util/StringUtils.h"
 
+// Sleep cover refresh strategy when dithered letterbox fill is active:
+// 1 = Double FAST_REFRESH (clear to white, then render content -- avoids HALF_REFRESH crosstalk)
+// 0 = Standard HALF_REFRESH (original behavior)
+#define USE_SLEEP_DOUBLE_FAST_REFRESH 1
+
 namespace {
 
 // Number of source pixels along the image edge to average for the dominant color
@@ -74,37 +79,6 @@ uint8_t quantizeBayerDither(int gray, int x, int y) {
   }
 }
 
-// Check whether a gray value would produce a dithered mix that crosses the
-// level-2 / level-3 boundary.  This is the ONLY boundary where some dithered
-// pixels are BLACK (level ≤ 2) and others are WHITE (level 3) in the BW pass,
-// creating a high-frequency checkerboard that causes e-ink display crosstalk
-// and washes out adjacent content during HALF_REFRESH.
-// Gray values 171-254 produce a level-2/level-3 mix via Bayer dithering.
-bool bayerCrossesBwBoundary(uint8_t gray) { return gray > 170 && gray < 255; }
-
-// Hash-based block dithering for BW-boundary gray values (171-254).
-// Each blockSize×blockSize pixel block gets a single uniform level (2 or 3),
-// determined by a deterministic spatial hash.  The proportion of level-3 blocks
-// approximates the target gray.  Unlike Bayer, the pattern is irregular
-// (noise-like), making it much less visually obvious at the same block size.
-// The hash is purely spatial (depends only on x, y, blockSize) so it produces
-// identical levels across BW, LSB, and MSB render passes.
-static constexpr int BW_DITHER_BLOCK = 2;
-
-uint8_t hashBlockDither(uint8_t avg, int x, int y) {
-  const int bx = x / BW_DITHER_BLOCK;
-  const int by = y / BW_DITHER_BLOCK;
-  // Fast mixing hash (splitmix32-inspired)
-  uint32_t h = (uint32_t)bx * 2654435761u ^ (uint32_t)by * 2246822519u;
-  h ^= h >> 16;
-  h *= 0x45d9f3bu;
-  h ^= h >> 16;
-  // Proportion of level-3 blocks needed to approximate the target gray
-  const float ratio = (avg - 170.0f) / 85.0f;
-  const uint32_t threshold = (uint32_t)(ratio * 4294967295.0f);
-  return (h < threshold) ? 3 : 2;
-}
-
 // --- Edge average cache ---
 // Caches the computed edge averages alongside the cover BMP so we don't rescan on every sleep.
 constexpr uint8_t EDGE_CACHE_VERSION = 2;
@@ -278,19 +252,6 @@ void drawLetterboxFill(GfxRenderer& renderer, const LetterboxFillData& data, uin
 
   const bool isSolid = (fillMode == CrossPointSettings::SLEEP_SCREEN_LETTERBOX_FILL::LETTERBOX_SOLID);
 
-  // For DITHERED mode with gray values in 171-254 (the level-2/level-3 BW boundary):
-  // Pixel-level Bayer dithering creates a regular high-frequency checkerboard in
-  // the BW pass that causes e-ink display crosstalk during HALF_REFRESH.
-  //
-  // Solution: HASH-BASED BLOCK DITHERING.  Each 2x2 pixel block gets a single
-  // level (2 or 3) determined by a spatial hash, with the proportion of level-3
-  // blocks tuned to approximate the target gray.  The 2px minimum run avoids BW
-  // crosstalk, and the irregular hash pattern is much less visible than a regular
-  // Bayer grid at the same block size.
-  const bool hashA = !isSolid && bayerCrossesBwBoundary(data.avgA);
-  const bool hashB = !isSolid && bayerCrossesBwBoundary(data.avgB);
-
-  // For solid mode: snap to nearest e-ink level
   const uint8_t levelA = isSolid ? snapToEinkLevel(data.avgA) / 85 : 0;
   const uint8_t levelB = isSolid ? snapToEinkLevel(data.avgB) / 85 : 0;
 
@@ -298,13 +259,7 @@ void drawLetterboxFill(GfxRenderer& renderer, const LetterboxFillData& data, uin
     if (data.letterboxA > 0) {
       for (int y = 0; y < data.letterboxA; y++)
         for (int x = 0; x < renderer.getScreenWidth(); x++) {
-          uint8_t lv;
-          if (isSolid)
-            lv = levelA;
-          else if (hashA)
-            lv = hashBlockDither(data.avgA, x, y);
-          else
-            lv = quantizeBayerDither(data.avgA, x, y);
+          const uint8_t lv = isSolid ? levelA : quantizeBayerDither(data.avgA, x, y);
           renderer.drawPixelGray(x, y, lv);
         }
     }
@@ -312,13 +267,7 @@ void drawLetterboxFill(GfxRenderer& renderer, const LetterboxFillData& data, uin
       const int start = renderer.getScreenHeight() - data.letterboxB;
       for (int y = start; y < renderer.getScreenHeight(); y++)
         for (int x = 0; x < renderer.getScreenWidth(); x++) {
-          uint8_t lv;
-          if (isSolid)
-            lv = levelB;
-          else if (hashB)
-            lv = hashBlockDither(data.avgB, x, y);
-          else
-            lv = quantizeBayerDither(data.avgB, x, y);
+          const uint8_t lv = isSolid ? levelB : quantizeBayerDither(data.avgB, x, y);
           renderer.drawPixelGray(x, y, lv);
         }
     }
@@ -326,13 +275,7 @@ void drawLetterboxFill(GfxRenderer& renderer, const LetterboxFillData& data, uin
     if (data.letterboxA > 0) {
       for (int x = 0; x < data.letterboxA; x++)
         for (int y = 0; y < renderer.getScreenHeight(); y++) {
-          uint8_t lv;
-          if (isSolid)
-            lv = levelA;
-          else if (hashA)
-            lv = hashBlockDither(data.avgA, x, y);
-          else
-            lv = quantizeBayerDither(data.avgA, x, y);
+          const uint8_t lv = isSolid ? levelA : quantizeBayerDither(data.avgA, x, y);
           renderer.drawPixelGray(x, y, lv);
         }
     }
@@ -340,13 +283,7 @@ void drawLetterboxFill(GfxRenderer& renderer, const LetterboxFillData& data, uin
       const int start = renderer.getScreenWidth() - data.letterboxB;
       for (int x = start; x < renderer.getScreenWidth(); x++)
         for (int y = 0; y < renderer.getScreenHeight(); y++) {
-          uint8_t lv;
-          if (isSolid)
-            lv = levelB;
-          else if (hashB)
-            lv = hashBlockDither(data.avgB, x, y);
-          else
-            lv = quantizeBayerDither(data.avgB, x, y);
+          const uint8_t lv = isSolid ? levelB : quantizeBayerDither(data.avgB, x, y);
           renderer.drawPixelGray(x, y, lv);
         }
     }
@@ -543,35 +480,47 @@ void SleepActivity::renderBitmapSleepScreen(const Bitmap& bitmap, const std::str
   const bool hasGreyscale = bitmap.hasGreyscale() &&
                             SETTINGS.sleepScreenCoverFilter == CrossPointSettings::SLEEP_SCREEN_COVER_FILTER::NO_FILTER;
 
-  // Draw letterbox fill (BW pass)
-  if (fillData.valid) {
-    drawLetterboxFill(renderer, fillData, fillMode);
-  }
+  const bool isInverted =
+      SETTINGS.sleepScreenCoverFilter == CrossPointSettings::SLEEP_SCREEN_COVER_FILTER::INVERTED_BLACK_AND_WHITE;
 
+#if USE_SLEEP_DOUBLE_FAST_REFRESH
+  const bool useDoubleFast =
+      fillData.valid && fillMode == CrossPointSettings::SLEEP_SCREEN_LETTERBOX_FILL::LETTERBOX_DITHERED;
+#else
+  const bool useDoubleFast = false;
+#endif
+
+  if (useDoubleFast) {
+    // Double FAST_REFRESH technique: avoids HALF_REFRESH crosstalk with dithered letterbox.
+    // Pass 1: clear to white baseline
+    renderer.clearScreen();
+    renderer.displayBuffer(HalDisplay::FAST_REFRESH);
+
+    // Pass 2: render actual content and display
+    if (fillData.valid) drawLetterboxFill(renderer, fillData, fillMode);
     renderer.drawBitmap(bitmap, x, y, pageWidth, pageHeight, cropX, cropY);
-
-  if (SETTINGS.sleepScreenCoverFilter == CrossPointSettings::SLEEP_SCREEN_COVER_FILTER::INVERTED_BLACK_AND_WHITE) {
-    renderer.invertScreen();
-  }
-
+    if (isInverted) renderer.invertScreen();
+    renderer.displayBuffer(HalDisplay::FAST_REFRESH);
+  } else {
+    // Standard path: single HALF_REFRESH
+    if (fillData.valid) drawLetterboxFill(renderer, fillData, fillMode);
+    renderer.drawBitmap(bitmap, x, y, pageWidth, pageHeight, cropX, cropY);
+    if (isInverted) renderer.invertScreen();
     renderer.displayBuffer(HalDisplay::HALF_REFRESH);
+  }
 
   if (hasGreyscale) {
     bitmap.rewindToData();
     renderer.clearScreen(0x00);
     renderer.setRenderMode(GfxRenderer::GRAYSCALE_LSB);
-    if (fillData.valid) {
-      drawLetterboxFill(renderer, fillData, fillMode);
-    }
+    if (fillData.valid) drawLetterboxFill(renderer, fillData, fillMode);
     renderer.drawBitmap(bitmap, x, y, pageWidth, pageHeight, cropX, cropY);
     renderer.copyGrayscaleLsbBuffers();
 
     bitmap.rewindToData();
     renderer.clearScreen(0x00);
     renderer.setRenderMode(GfxRenderer::GRAYSCALE_MSB);
-    if (fillData.valid) {
-      drawLetterboxFill(renderer, fillData, fillMode);
-    }
+    if (fillData.valid) drawLetterboxFill(renderer, fillData, fillMode);
     renderer.drawBitmap(bitmap, x, y, pageWidth, pageHeight, cropX, cropY);
     renderer.copyGrayscaleMsbBuffers();
 

src/activities/reader/EpubReaderActivity.cpp

@@ -22,11 +22,6 @@
 #include "util/BookmarkStore.h"
 #include "util/Dictionary.h"
 
-// Image refresh optimization strategy:
-// 0 = Use double FAST_REFRESH technique (default, feels snappier)
-// 1 = Use displayWindow() for partial refresh (experimental)
-#define USE_IMAGE_DOUBLE_FAST_REFRESH 0
-
 namespace {
 // pagesPerRefresh now comes from SETTINGS.getRefreshFrequency()
 constexpr unsigned long skipChapterMs = 700;
@@ -1022,13 +1017,8 @@ void EpubReaderActivity::saveProgress(int spineIndex, int currentPage, int pageC
 void EpubReaderActivity::renderContents(std::unique_ptr<Page> page, const int orientedMarginTop,
                                         const int orientedMarginRight, const int orientedMarginBottom,
                                         const int orientedMarginLeft) {
-  // Determine if this page needs special image handling
-  bool pageHasImages = page->hasImages();
-  bool useAntiAliasing = SETTINGS.textAntiAliasing;
-
-  // Force half refresh for pages with images when anti-aliasing is on,
-  // as grayscale tones require half refresh to display correctly
-  bool forceFullRefresh = pageHasImages && useAntiAliasing;
+  // Force special handling for pages with images when anti-aliasing is on
+  bool imagePageWithAA = page->hasImages() && SETTINGS.textAntiAliasing;
 
   page->render(renderer, SETTINGS.getReaderFontId(), orientedMarginLeft, orientedMarginTop);
 
@@ -1048,42 +1038,26 @@ void EpubReaderActivity::renderContents(std::unique_ptr<Page> page, const int or
   }
 
   renderStatusBar(orientedMarginRight, orientedMarginBottom, orientedMarginLeft);
-
-  // Check if half-refresh is needed (either entering Reader or pages counter reached)
-  if (pagesUntilFullRefresh <= 1) {
-    renderer.displayBuffer(HalDisplay::HALF_REFRESH);
-    pagesUntilFullRefresh = SETTINGS.getRefreshFrequency();
-  } else if (forceFullRefresh) {
-    // OPTIMIZATION: For image pages with anti-aliasing, use fast double-refresh technique
-    // to reduce perceived lag. Only when pagesUntilFullRefresh > 1 (screen already clean).
+  if (imagePageWithAA) {
+    // Double FAST_REFRESH with selective image blanking (pablohc's technique):
+    // HALF_REFRESH sets particles too firmly for the grayscale LUT to adjust.
+    // Instead, blank only the image area and do two fast refreshes.
     int imgX, imgY, imgW, imgH;
     if (page->getImageBoundingBox(imgX, imgY, imgW, imgH)) {
-      int screenX = imgX + orientedMarginLeft;
-      int screenY = imgY + orientedMarginTop;
-      LOG_DBG("ERS", "Image page: fast double-refresh (page bbox: %d,%d %dx%d, screen: %d,%d %dx%d)", imgX, imgY, imgW,
-              imgH, screenX, screenY, imgW, imgH);
+      renderer.fillRect(imgX + orientedMarginLeft, imgY + orientedMarginTop, imgW, imgH, false);
+      renderer.displayBuffer(HalDisplay::FAST_REFRESH);
 
-#if USE_IMAGE_DOUBLE_FAST_REFRESH == 0
-      // Method A: Fill blank area + two FAST_REFRESH operations
-      renderer.fillRect(screenX, screenY, imgW, imgH, false);
-      renderer.displayBuffer(HalDisplay::FAST_REFRESH);
       page->render(renderer, SETTINGS.getReaderFontId(), orientedMarginLeft, orientedMarginTop);
       renderStatusBar(orientedMarginRight, orientedMarginBottom, orientedMarginLeft);
       renderer.displayBuffer(HalDisplay::FAST_REFRESH);
-#else
-      // Method B (experimental): Use displayWindow() for partial refresh
-      renderer.displayBuffer(HalDisplay::FAST_REFRESH);
-      page->render(renderer, SETTINGS.getReaderFontId(), orientedMarginLeft, orientedMarginTop);
-      renderStatusBar(orientedMarginRight, orientedMarginBottom, orientedMarginLeft);
-      renderer.displayWindow(screenX, screenY, imgW, imgH, HalDisplay::FAST_REFRESH);
-#endif
     } else {
-      LOG_DBG("ERS", "Image page but no bbox, using standard half refresh");
       renderer.displayBuffer(HalDisplay::HALF_REFRESH);
     }
-    pagesUntilFullRefresh--;
+    // Double FAST_REFRESH handles ghosting for image pages; don't count toward full refresh cadence
+  } else if (pagesUntilFullRefresh <= 1) {
+    renderer.displayBuffer(HalDisplay::HALF_REFRESH);
+    pagesUntilFullRefresh = SETTINGS.getRefreshFrequency();
   } else {
-    // Normal page without images, or images without anti-aliasing
     renderer.displayBuffer();
     pagesUntilFullRefresh--;
   }