feat: Extend high contrast mode to entire UI

- Add global high contrast mode flag in BitmapHelpers
- Modify quantization thresholds for high contrast rendering
- Update ditherer classes (Atkinson, Floyd-Steinberg) for contrast mode
- Add displayContrast setting with persistence
- Add "High Contrast" toggle in display settings
- Apply high contrast mode on startup from saved settings

lib/GfxRenderer/BitmapHelpers.cpp

@@ -2,6 +2,17 @@
 
 #include <cstdint>
 
+// Global high contrast mode flag
+static bool g_highContrastMode = false;
+
+void setHighContrastMode(bool enabled) {
+  g_highContrastMode = enabled;
+}
+
+bool isHighContrastMode() {
+  return g_highContrastMode;
+}
+
 // Brightness/Contrast adjustments:
 constexpr bool USE_BRIGHTNESS = false;       // true: apply brightness/gamma adjustments
 constexpr int BRIGHTNESS_BOOST = 10;         // Brightness offset (0-50)
@@ -52,6 +63,19 @@ int adjustPixel(int gray) {
 // Simple quantization without dithering - divide into 4 levels
 // The thresholds are fine-tuned to the X4 display
 uint8_t quantizeSimple(int gray) {
+  if (g_highContrastMode) {
+    // High contrast: push mid-grays toward black/white
+    if (gray < 60) {
+      return 0;
+    } else if (gray < 100) {
+      return 1;
+    } else if (gray < 180) {
+      return 2;
+    } else {
+      return 3;
+    }
+  } else {
+    // Normal thresholds
     if (gray < 45) {
       return 0;
     } else if (gray < 70) {
@@ -62,6 +86,7 @@ uint8_t quantizeSimple(int gray) {
       return 3;
     }
   }
+}
 
 // Hash-based noise dithering - survives downsampling without moiré artifacts
 // Uses integer hash to generate pseudo-random threshold per pixel

lib/GfxRenderer/BitmapHelpers.h

@@ -2,6 +2,11 @@
 
 #include <cstring>
 
+// Global high contrast mode control
+// When enabled, quantization thresholds are adjusted to push mid-grays toward black/white
+void setHighContrastMode(bool enabled);
+bool isHighContrastMode();
+
 // Helper functions
 uint8_t quantize(int gray, int x, int y);
 uint8_t quantizeSimple(int gray);
@@ -122,21 +127,23 @@ class AtkinsonDitherer {
     // Quantize to 4 levels
     uint8_t quantized;
     int quantizedValue;
-    if (false) {  // original thresholds
+    if (isHighContrastMode()) {
-      if (adjusted < 43) {
+      // High contrast thresholds - push mid-grays toward extremes
+      if (adjusted < 50) {
         quantized = 0;
-        quantizedValue = 0;
+        quantizedValue = 15;
-      } else if (adjusted < 128) {
+      } else if (adjusted < 90) {
         quantized = 1;
-        quantizedValue = 85;
+        quantizedValue = 50;
-      } else if (adjusted < 213) {
+      } else if (adjusted < 170) {
         quantized = 2;
-        quantizedValue = 170;
+        quantizedValue = 130;
       } else {
         quantized = 3;
-        quantizedValue = 255;
+        quantizedValue = 230;
       }
-    } else {  // fine-tuned to X4 eink display
+    } else {
+      // Normal thresholds - fine-tuned to X4 eink display
       if (adjusted < 30) {
         quantized = 0;
         quantizedValue = 15;
@@ -223,24 +230,26 @@ class FloydSteinbergDitherer {
     if (adjusted < 0) adjusted = 0;
     if (adjusted > 255) adjusted = 255;
 
-    // Quantize to 4 levels (0, 85, 170, 255)
+    // Quantize to 4 levels
     uint8_t quantized;
     int quantizedValue;
-    if (false) {  // original thresholds
+    if (isHighContrastMode()) {
-      if (adjusted < 43) {
+      // High contrast thresholds - push mid-grays toward extremes
+      if (adjusted < 50) {
         quantized = 0;
-        quantizedValue = 0;
+        quantizedValue = 15;
-      } else if (adjusted < 128) {
+      } else if (adjusted < 90) {
         quantized = 1;
-        quantizedValue = 85;
+        quantizedValue = 50;
-      } else if (adjusted < 213) {
+      } else if (adjusted < 170) {
         quantized = 2;
-        quantizedValue = 170;
+        quantizedValue = 130;
       } else {
         quantized = 3;
-        quantizedValue = 255;
+        quantizedValue = 230;
       }
-    } else {  // fine-tuned to X4 eink display
+    } else {
+      // Normal thresholds - fine-tuned to X4 eink display
       if (adjusted < 30) {
         quantized = 0;
         quantizedValue = 15;

src/CrossPointSettings.cpp

@@ -23,7 +23,7 @@ void readAndValidate(FsFile& file, uint8_t& member, const uint8_t maxValue) {
 namespace {
 constexpr uint8_t SETTINGS_FILE_VERSION = 1;
 // Increment this when adding new persisted settings fields
-constexpr uint8_t SETTINGS_COUNT = 26;  // 25 + sleepScreenCoverFilter
+constexpr uint8_t SETTINGS_COUNT = 27;  // 26 + displayContrast
 constexpr char SETTINGS_FILE[] = "/.crosspoint/settings.bin";
 }  // namespace
 
@@ -66,6 +66,8 @@ bool CrossPointSettings::saveToFile() const {
   serialization::writeString(outputFile, std::string(opdsPassword));
   // PR #476: B&W filter for cover images
   serialization::writePod(outputFile, sleepScreenCoverFilter);
+  // System-wide display contrast
+  serialization::writePod(outputFile, displayContrast);
   // New fields added at end for backward compatibility
   outputFile.close();
 
@@ -167,6 +169,9 @@ bool CrossPointSettings::loadFromFile() {
     // PR #476: B&W filter for cover images
     readAndValidate(inputFile, sleepScreenCoverFilter, SLEEP_SCREEN_COVER_FILTER_COUNT);
     if (++settingsRead >= fileSettingsCount) break;
+    // System-wide display contrast (0 = normal, 1 = high)
+    serialization::readPod(inputFile, displayContrast);
+    if (++settingsRead >= fileSettingsCount) break;
     // New fields added at end for backward compatibility
   } while (false);
 

src/CrossPointSettings.h

@@ -133,6 +133,8 @@ class CrossPointSettings {
   uint8_t hideBatteryPercentage = HIDE_NEVER;
   // Long-press chapter skip on side buttons
   uint8_t longPressChapterSkip = 1;
+  // System-wide display contrast (0 = normal, 1 = high)
+  uint8_t displayContrast = 0;
 
   // Pinned list name (empty = none pinned)
   char pinnedListName[64] = "";

src/activities/settings/CategorySettingsActivity.cpp

@@ -1,5 +1,6 @@
 #include "CategorySettingsActivity.h"
 
+#include <BitmapHelpers.h>
 #include <GfxRenderer.h>
 #include <HardwareSerial.h>
 
@@ -115,6 +116,11 @@ void CategorySettingsActivity::toggleCurrentSetting() {
     // Toggle the boolean value using the member pointer
     const bool currentValue = SETTINGS.*(setting.valuePtr);
     SETTINGS.*(setting.valuePtr) = !currentValue;
+
+    // Handle side effects for specific settings
+    if (setting.valuePtr == &CrossPointSettings::displayContrast) {
+      setHighContrastMode(SETTINGS.displayContrast == 1);
+    }
   } else if (setting.type == SettingType::ENUM && setting.valuePtr != nullptr) {
     const uint8_t currentValue = SETTINGS.*(setting.valuePtr);
     SETTINGS.*(setting.valuePtr) = (currentValue + 1) % static_cast<uint8_t>(setting.enumValues.size());

src/activities/settings/SettingsActivity.cpp

@@ -19,6 +19,7 @@ const SettingInfo displaySettings[displaySettingsCount] = {
     SettingInfo::Enum("Sleep Screen Cover Mode", &CrossPointSettings::sleepScreenCoverMode, {"Fit", "Crop", "Actual"}),
     SettingInfo::Enum("Sleep Screen Cover Filter", &CrossPointSettings::sleepScreenCoverFilter,
                       {"None", "Contrast", "Inverted"}),
+    SettingInfo::Toggle("High Contrast", &CrossPointSettings::displayContrast),
     SettingInfo::Enum("Status Bar", &CrossPointSettings::statusBar,
                       {"None", "No Progress", "Full w/ Percentage", "Full w/ Progress Bar", "Progress Bar"}),
     SettingInfo::Enum("Hide Battery %", &CrossPointSettings::hideBatteryPercentage, {"Never", "In Reader", "Always"}),

src/main.cpp

@@ -6,9 +6,12 @@
 #include <SDCardManager.h>
 #include <SPI.h>
 #include <builtinFonts/all.h>
+#include <esp_heap_caps.h>
 
 #include <cstring>
 
+#include <BitmapHelpers.h>
+
 #include "Battery.h"
 #include "BookListStore.h"
 #include "CrossPointSettings.h"
@@ -470,6 +473,8 @@ void setup() {
   }
 
   SETTINGS.loadFromFile();
+  // Apply high contrast mode from settings
+  setHighContrastMode(SETTINGS.displayContrast == 1);
 
   if (isWakeupByPowerButton()) {
     // For normal wakeups, verify power button press duration