From 003e635a56c38d0530a69fa628b7395780837884 Mon Sep 17 00:00:00 2001
From: keringo <>
Date: Wed, 25 Jun 2025 21:08:54 +0300
Subject: [PATCH 01/15] black_hex & white_hex added

---
 drawcontext.h                         |  2 ++
 ffi-cdecl/wrap-mupdf_cdecl.c          |  1 +
 ffi/drawcontext.lua                   | 10 ++++++++--
 ffi/koptcontext.lua                   |  8 ++++++++
 ffi/koptcontext_h.lua                 |  2 ++
 ffi/mupdf.lua                         |  1 +
 ffi/mupdf_h.lua                       |  1 +
 thirdparty/libk2pdfopt/CMakeLists.txt |  2 +-
 8 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/drawcontext.h b/drawcontext.h
index f601de148..32df06574 100644
--- a/drawcontext.h
+++ b/drawcontext.h
@@ -22,6 +22,8 @@ typedef struct DrawContext {
 	int rotate;
 	double zoom;
 	double gamma;
+	int black_hex;
+	int white_hex;
 	int offset_x;
 	int offset_y;
 } DrawContext;
diff --git a/ffi-cdecl/wrap-mupdf_cdecl.c b/ffi-cdecl/wrap-mupdf_cdecl.c
index ba9610c1c..b33fa8eb8 100644
--- a/ffi-cdecl/wrap-mupdf_cdecl.c
+++ b/ffi-cdecl/wrap-mupdf_cdecl.c
@@ -122,6 +122,7 @@ cdecl_func(mupdf_convert_pixmap)
 cdecl_func(fz_drop_pixmap)
 cdecl_func(fz_clear_pixmap_with_value)
 cdecl_func(fz_gamma_pixmap)
+cdecl_func(fz_tint_pixmap)
 cdecl_func(fz_scale_pixmap)
 cdecl_func(fz_pixmap_width)
 cdecl_func(fz_pixmap_height)
diff --git a/ffi/drawcontext.lua b/ffi/drawcontext.lua
index 1886cbeac..9db118260 100644
--- a/ffi/drawcontext.lua
+++ b/ffi/drawcontext.lua
@@ -11,6 +11,8 @@ typedef struct DrawContext {
 	int rotate;
 	double zoom;
 	double gamma;
+	int black_hex;
+	int white_hex;
 	int offset_x;
 	int offset_y;
 } DrawContext;
@@ -30,11 +32,15 @@ end
 function DC_mt.__index:getOffset() return self.offset_x, self.offset_y end
 function DC_mt.__index:setGamma(gamma) self.gamma = gamma end
 function DC_mt.__index:getGamma() return self.gamma end
+function DC_mt.__index:setBlackHex(black_hex) self.black_hex = black_hex end
+function DC_mt.__index:getBlackHex() return self.black_hex end
+function DC_mt.__index:setWhiteHex(white_hex) self.white_hex = white_hex end
+function DC_mt.__index:getWhiteHex() return self.white_hex end
 
 local dctype = ffi.metatype("DrawContext", DC_mt)
 
-function DC.new(rotate, zoom, x, y, gamma)
-	return dctype(rotate or 0, zoom or 1.0, gamma or -1.0, x or 0, y or 0)
+function DC.new(rotate, zoom, x, y, gamma, black_hex, white_hex)
+	return dctype(rotate or 0, zoom or 1.0, gamma or -1.0, x or 0, y or 0, black_hex or 0x000000, white_hex or 0xFFFFFF)
 end
 
 return DC
diff --git a/ffi/koptcontext.lua b/ffi/koptcontext.lua
index 83c495ec5..63c0d9e73 100644
--- a/ffi/koptcontext.lua
+++ b/ffi/koptcontext.lua
@@ -191,6 +191,8 @@ function KOPTContext_mt.__index:setMargin(margin) self.margin = margin end
 function KOPTContext_mt.__index:setZoom(zoom) self.zoom = zoom end
 function KOPTContext_mt.__index:setQuality(quality) self.quality = quality end
 function KOPTContext_mt.__index:setContrast(contrast) self.contrast = contrast end
+function KOPTContext_mt.__index:setBlackHex(black_hex) self.black_hex = black_hex end
+function KOPTContext_mt.__index:setWhiteHex(white_hex) self.white_hex = white_hex end
 function KOPTContext_mt.__index:setDefectSize(defect_size) self.defect_size = defect_size end
 function KOPTContext_mt.__index:setLineSpacing(line_spacing) self.line_spacing = line_spacing end
 function KOPTContext_mt.__index:setWordSpacing(word_spacing) self.word_spacing = word_spacing end
@@ -614,6 +616,8 @@ function KOPTContext.new()
     kc.read_max_width = 3000
     kc.read_max_height = 4000
     kc.writing_direction = 0
+	kc.black_hex = 0x000000
+	kc.white_hex = 0xFFFFFF
     -- number values
     kc.zoom = 1.0
     kc.margin = 0.06
@@ -684,6 +688,8 @@ function KOPTContext.totable(kc)
     context.read_max_width = kc.read_max_width
     context.read_max_height = kc.read_max_height
     context.writing_direction = kc.writing_direction
+	context.black_hex = kc.black_hex
+	context.white_hex = kc.white_hex
     -- number values
     context.zoom = kc.zoom
     context.margin = kc.margin
@@ -754,6 +760,8 @@ function KOPTContext.fromtable(context)
     kc.read_max_width = context.read_max_width
     kc.read_max_height = context.read_max_height
     kc.writing_direction = context.writing_direction
+	kc.black_hex = context.black_hex
+	kc.white_hex = context.white_hex
     -- number values
     kc.zoom = context.zoom
     kc.margin = context.margin
diff --git a/ffi/koptcontext_h.lua b/ffi/koptcontext_h.lua
index 3e5b33de0..5f37b1ec8 100644
--- a/ffi/koptcontext_h.lua
+++ b/ffi/koptcontext_h.lua
@@ -125,6 +125,8 @@ struct KOPTContext {
   int read_max_width;
   int read_max_height;
   int writing_direction;
+  int black_hex;
+  int white_hex;
   double zoom;
   double margin;
   double quality;
diff --git a/ffi/mupdf.lua b/ffi/mupdf.lua
index a638f9286..31116cc5f 100644
--- a/ffi/mupdf.lua
+++ b/ffi/mupdf.lua
@@ -689,6 +689,7 @@ function page_mt.__index:draw_new(draw_context, width, height, offset_x, offset_
         M.fz_gamma_pixmap(self.ctx, pix, draw_context.gamma)
     end
 
+	M.fz_tint_pixmap(self.ctx, pix, draw_context.black_hex, draw_context.white_hex)
     M.fz_drop_pixmap(self.ctx, pix)
 
     return bb
diff --git a/ffi/mupdf_h.lua b/ffi/mupdf_h.lua
index 91ccc08ad..e1deda680 100644
--- a/ffi/mupdf_h.lua
+++ b/ffi/mupdf_h.lua
@@ -226,6 +226,7 @@ fz_pixmap *mupdf_convert_pixmap(fz_context *, const fz_pixmap *, fz_colorspace *
 void fz_drop_pixmap(fz_context *, fz_pixmap *);
 void fz_clear_pixmap_with_value(fz_context *, fz_pixmap *, int);
 void fz_gamma_pixmap(fz_context *, fz_pixmap *, float);
+void fz_tint_pixmap(fz_context *, fz_pixmap *, int, int);
 fz_pixmap *fz_scale_pixmap(fz_context *, fz_pixmap *, float, float, float, float, const fz_irect *);
 int fz_pixmap_width(fz_context *, const fz_pixmap *);
 int fz_pixmap_height(fz_context *, const fz_pixmap *);
diff --git a/thirdparty/libk2pdfopt/CMakeLists.txt b/thirdparty/libk2pdfopt/CMakeLists.txt
index 23912a57b..0287959a7 100644
--- a/thirdparty/libk2pdfopt/CMakeLists.txt
+++ b/thirdparty/libk2pdfopt/CMakeLists.txt
@@ -21,7 +21,7 @@ endif()
 
 external_project(
     DOWNLOAD GIT 59ced371378312d8f332d9a35f5b4a3c33b18954
-    https://github.com/koreader/libk2pdfopt.git
+    https://github.com/kerivin/libk2pdfopt.git
     PATCH_COMMAND ${PATCH_CMD}
     CMAKE_ARGS ${CMAKE_ARGS}
     SOURCE_SUBDIR lib

From 8b544c9a3b2b10aa3706a47aec5ad7429ce08030 Mon Sep 17 00:00:00 2001
From: keringo <>
Date: Wed, 25 Jun 2025 21:26:51 +0300
Subject: [PATCH 02/15] tabs -> spaces

---
 ffi/mupdf.lua | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/ffi/mupdf.lua b/ffi/mupdf.lua
index 31116cc5f..b7b9f9956 100644
--- a/ffi/mupdf.lua
+++ b/ffi/mupdf.lua
@@ -689,7 +689,7 @@ function page_mt.__index:draw_new(draw_context, width, height, offset_x, offset_
         M.fz_gamma_pixmap(self.ctx, pix, draw_context.gamma)
     end
 
-	M.fz_tint_pixmap(self.ctx, pix, draw_context.black_hex, draw_context.white_hex)
+    M.fz_tint_pixmap(self.ctx, pix, draw_context.black_hex, draw_context.white_hex)
     M.fz_drop_pixmap(self.ctx, pix)
 
     return bb

From 950c35b4e76e3782a0fa1e43edef02018f97c8a6 Mon Sep 17 00:00:00 2001
From: keringo <>
Date: Thu, 26 Jun 2025 17:33:36 +0300
Subject: [PATCH 03/15] white_threshold

---
 drawcontext.h                |  3 +--
 ffi-cdecl/wrap-mupdf_cdecl.c |  1 -
 ffi/drawcontext.lua          | 13 +++++--------
 ffi/koptcontext.lua          |  8 --------
 ffi/koptcontext_h.lua        |  2 --
 ffi/mupdf.lua                |  1 -
 ffi/mupdf_h.lua              |  1 -
 7 files changed, 6 insertions(+), 23 deletions(-)

diff --git a/drawcontext.h b/drawcontext.h
index 32df06574..0c4d8c635 100644
--- a/drawcontext.h
+++ b/drawcontext.h
@@ -22,8 +22,7 @@ typedef struct DrawContext {
 	int rotate;
 	double zoom;
 	double gamma;
-	int black_hex;
-	int white_hex;
+	int white_threshold;
 	int offset_x;
 	int offset_y;
 } DrawContext;
diff --git a/ffi-cdecl/wrap-mupdf_cdecl.c b/ffi-cdecl/wrap-mupdf_cdecl.c
index b33fa8eb8..ba9610c1c 100644
--- a/ffi-cdecl/wrap-mupdf_cdecl.c
+++ b/ffi-cdecl/wrap-mupdf_cdecl.c
@@ -122,7 +122,6 @@ cdecl_func(mupdf_convert_pixmap)
 cdecl_func(fz_drop_pixmap)
 cdecl_func(fz_clear_pixmap_with_value)
 cdecl_func(fz_gamma_pixmap)
-cdecl_func(fz_tint_pixmap)
 cdecl_func(fz_scale_pixmap)
 cdecl_func(fz_pixmap_width)
 cdecl_func(fz_pixmap_height)
diff --git a/ffi/drawcontext.lua b/ffi/drawcontext.lua
index 9db118260..26791d302 100644
--- a/ffi/drawcontext.lua
+++ b/ffi/drawcontext.lua
@@ -11,8 +11,7 @@ typedef struct DrawContext {
 	int rotate;
 	double zoom;
 	double gamma;
-	int black_hex;
-	int white_hex;
+	unsigned char white_threshold;
 	int offset_x;
 	int offset_y;
 } DrawContext;
@@ -32,15 +31,13 @@ end
 function DC_mt.__index:getOffset() return self.offset_x, self.offset_y end
 function DC_mt.__index:setGamma(gamma) self.gamma = gamma end
 function DC_mt.__index:getGamma() return self.gamma end
-function DC_mt.__index:setBlackHex(black_hex) self.black_hex = black_hex end
-function DC_mt.__index:getBlackHex() return self.black_hex end
-function DC_mt.__index:setWhiteHex(white_hex) self.white_hex = white_hex end
-function DC_mt.__index:getWhiteHex() return self.white_hex end
+function DC_mt.__index:setWhiteThreshold(white_threshold) self.white_threshold = white_threshold end
+function DC_mt.__index:getWhiteThreshold() return self.white_threshold end
 
 local dctype = ffi.metatype("DrawContext", DC_mt)
 
-function DC.new(rotate, zoom, x, y, gamma, black_hex, white_hex)
-	return dctype(rotate or 0, zoom or 1.0, gamma or -1.0, x or 0, y or 0, black_hex or 0x000000, white_hex or 0xFFFFFF)
+function DC.new(rotate, zoom, x, y, gamma, white_threshold)
+	return dctype(rotate or 0, zoom or 1.0, gamma or -1.0, x or 0, y or 0, white_threshold or 255)
 end
 
 return DC
diff --git a/ffi/koptcontext.lua b/ffi/koptcontext.lua
index 63c0d9e73..83c495ec5 100644
--- a/ffi/koptcontext.lua
+++ b/ffi/koptcontext.lua
@@ -191,8 +191,6 @@ function KOPTContext_mt.__index:setMargin(margin) self.margin = margin end
 function KOPTContext_mt.__index:setZoom(zoom) self.zoom = zoom end
 function KOPTContext_mt.__index:setQuality(quality) self.quality = quality end
 function KOPTContext_mt.__index:setContrast(contrast) self.contrast = contrast end
-function KOPTContext_mt.__index:setBlackHex(black_hex) self.black_hex = black_hex end
-function KOPTContext_mt.__index:setWhiteHex(white_hex) self.white_hex = white_hex end
 function KOPTContext_mt.__index:setDefectSize(defect_size) self.defect_size = defect_size end
 function KOPTContext_mt.__index:setLineSpacing(line_spacing) self.line_spacing = line_spacing end
 function KOPTContext_mt.__index:setWordSpacing(word_spacing) self.word_spacing = word_spacing end
@@ -616,8 +614,6 @@ function KOPTContext.new()
     kc.read_max_width = 3000
     kc.read_max_height = 4000
     kc.writing_direction = 0
-	kc.black_hex = 0x000000
-	kc.white_hex = 0xFFFFFF
     -- number values
     kc.zoom = 1.0
     kc.margin = 0.06
@@ -688,8 +684,6 @@ function KOPTContext.totable(kc)
     context.read_max_width = kc.read_max_width
     context.read_max_height = kc.read_max_height
     context.writing_direction = kc.writing_direction
-	context.black_hex = kc.black_hex
-	context.white_hex = kc.white_hex
     -- number values
     context.zoom = kc.zoom
     context.margin = kc.margin
@@ -760,8 +754,6 @@ function KOPTContext.fromtable(context)
     kc.read_max_width = context.read_max_width
     kc.read_max_height = context.read_max_height
     kc.writing_direction = context.writing_direction
-	kc.black_hex = context.black_hex
-	kc.white_hex = context.white_hex
     -- number values
     kc.zoom = context.zoom
     kc.margin = context.margin
diff --git a/ffi/koptcontext_h.lua b/ffi/koptcontext_h.lua
index 5f37b1ec8..3e5b33de0 100644
--- a/ffi/koptcontext_h.lua
+++ b/ffi/koptcontext_h.lua
@@ -125,8 +125,6 @@ struct KOPTContext {
   int read_max_width;
   int read_max_height;
   int writing_direction;
-  int black_hex;
-  int white_hex;
   double zoom;
   double margin;
   double quality;
diff --git a/ffi/mupdf.lua b/ffi/mupdf.lua
index b7b9f9956..a638f9286 100644
--- a/ffi/mupdf.lua
+++ b/ffi/mupdf.lua
@@ -689,7 +689,6 @@ function page_mt.__index:draw_new(draw_context, width, height, offset_x, offset_
         M.fz_gamma_pixmap(self.ctx, pix, draw_context.gamma)
     end
 
-    M.fz_tint_pixmap(self.ctx, pix, draw_context.black_hex, draw_context.white_hex)
     M.fz_drop_pixmap(self.ctx, pix)
 
     return bb
diff --git a/ffi/mupdf_h.lua b/ffi/mupdf_h.lua
index e1deda680..91ccc08ad 100644
--- a/ffi/mupdf_h.lua
+++ b/ffi/mupdf_h.lua
@@ -226,7 +226,6 @@ fz_pixmap *mupdf_convert_pixmap(fz_context *, const fz_pixmap *, fz_colorspace *
 void fz_drop_pixmap(fz_context *, fz_pixmap *);
 void fz_clear_pixmap_with_value(fz_context *, fz_pixmap *, int);
 void fz_gamma_pixmap(fz_context *, fz_pixmap *, float);
-void fz_tint_pixmap(fz_context *, fz_pixmap *, int, int);
 fz_pixmap *fz_scale_pixmap(fz_context *, fz_pixmap *, float, float, float, float, const fz_irect *);
 int fz_pixmap_width(fz_context *, const fz_pixmap *);
 int fz_pixmap_height(fz_context *, const fz_pixmap *);

From 9bf6abb4caeb9088b0b7657957e481067eafdb03 Mon Sep 17 00:00:00 2001
From: keringo <>
Date: Thu, 26 Jun 2025 18:27:03 +0300
Subject: [PATCH 04/15] mupdf white threshold

---
 ffi/mupdf.lua | 30 +++++++++++++++++++++++++++++-
 1 file changed, 29 insertions(+), 1 deletion(-)

diff --git a/ffi/mupdf.lua b/ffi/mupdf.lua
index a638f9286..e5f5be02e 100644
--- a/ffi/mupdf.lua
+++ b/ffi/mupdf.lua
@@ -647,6 +647,32 @@ local function run_page(page, pixmap, ctm)
     M.fz_drop_device(page.ctx, dev)
     if ok == nil then merror(page.ctx, "could not run page") end
 end
+
+local function apply_white_threshold(bytes_per_pixel, samples, pixel_count, white_threshold)
+    local strength_coeff = 4
+    if bytes_per_pixel == 4 then
+        for i = 0, pixel_count - 1 do
+            local idx = i * bytes_per_pixel
+            local r, g, b = samples[idx], samples[idx + 1], samples[idx + 2]
+            local brightness = 0.299 * r + 0.587 * g + 0.114 * b
+            local strength = math.min(strength_coeff * (brightness - white_threshold) / (255 - white_threshold), 1.0)
+            if brightness > white_threshold then
+                samples[idx]     = r + (255 - r) * strength
+                samples[idx + 1] = g + (255 - g) * strength
+                samples[idx + 2] = b + (255 - b) * strength
+            end
+        end
+    else
+        for i = 0, pixel_count - 1 do
+            local brightness = samples[i]
+            if brightness > white_threshold then
+                local strength = math.min(strength_coeff * (brightness - white_threshold) / (255 - white_threshold), 1.0)
+                samples[i] = brightness + (255 - brightness) * strength
+            end
+        end
+    end
+end
+
 --[[
 render page to blitbuffer
 
@@ -679,11 +705,13 @@ function page_mt.__index:draw_new(draw_context, width, height, offset_x, offset_
     if mupdf.bgr and self.doc.color then
         colorspace = M.fz_device_bgr(self.ctx)
     end
+    local samples = ffi.cast("unsigned char*", bb.data)
     local pix = W.mupdf_new_pixmap_with_bbox_and_data(
-        self.ctx, colorspace, bbox, nil, self.doc.color and 1 or 0, ffi.cast("unsigned char*", bb.data))
+        self.ctx, colorspace, bbox, nil, self.doc.color and 1 or 0, samples)
     if pix == nil then merror(self.ctx, "cannot allocate pixmap") end
 
     run_page(self, pix, ctm)
+    apply_white_threshold(self.doc.color and 4 or 1, samples, width * height, draw_context.white_threshold)
 
     if draw_context.gamma >= 0.0 then
         M.fz_gamma_pixmap(self.ctx, pix, draw_context.gamma)

From fe1962ebf907014e41f2929043bb2364eeacbe6c Mon Sep 17 00:00:00 2001
From: keringo <>
Date: Thu, 26 Jun 2025 18:34:35 +0300
Subject: [PATCH 05/15] max 255 channel brightness restriction

---
 ffi/mupdf.lua | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/ffi/mupdf.lua b/ffi/mupdf.lua
index e5f5be02e..d98d6b815 100644
--- a/ffi/mupdf.lua
+++ b/ffi/mupdf.lua
@@ -657,9 +657,9 @@ local function apply_white_threshold(bytes_per_pixel, samples, pixel_count, whit
             local brightness = 0.299 * r + 0.587 * g + 0.114 * b
             local strength = math.min(strength_coeff * (brightness - white_threshold) / (255 - white_threshold), 1.0)
             if brightness > white_threshold then
-                samples[idx]     = r + (255 - r) * strength
-                samples[idx + 1] = g + (255 - g) * strength
-                samples[idx + 2] = b + (255 - b) * strength
+                samples[idx]     = math.max(255, r + (255 - r) * strength)
+                samples[idx + 1] = math.max(255, g + (255 - g) * strength)
+                samples[idx + 2] = math.max(255, b + (255 - b) * strength)
             end
         end
     else
@@ -667,7 +667,7 @@ local function apply_white_threshold(bytes_per_pixel, samples, pixel_count, whit
             local brightness = samples[i]
             if brightness > white_threshold then
                 local strength = math.min(strength_coeff * (brightness - white_threshold) / (255 - white_threshold), 1.0)
-                samples[i] = brightness + (255 - brightness) * strength
+                samples[i] = math.max(255, brightness + (255 - brightness) * strength)
             end
         end
     end

From 33de636965fd6e506deeff0fa2cea2502535ad21 Mon Sep 17 00:00:00 2001
From: keringo <>
Date: Thu, 26 Jun 2025 18:50:18 +0300
Subject: [PATCH 06/15] minor improvements

---
 drawcontext.h                         | 2 +-
 ffi/mupdf.lua                         | 2 +-
 thirdparty/libk2pdfopt/CMakeLists.txt | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/drawcontext.h b/drawcontext.h
index 0c4d8c635..ae0d0dff9 100644
--- a/drawcontext.h
+++ b/drawcontext.h
@@ -22,7 +22,7 @@ typedef struct DrawContext {
 	int rotate;
 	double zoom;
 	double gamma;
-	int white_threshold;
+	unsigned char white_threshold;
 	int offset_x;
 	int offset_y;
 } DrawContext;
diff --git a/ffi/mupdf.lua b/ffi/mupdf.lua
index d98d6b815..162cd3d6f 100644
--- a/ffi/mupdf.lua
+++ b/ffi/mupdf.lua
@@ -655,8 +655,8 @@ local function apply_white_threshold(bytes_per_pixel, samples, pixel_count, whit
             local idx = i * bytes_per_pixel
             local r, g, b = samples[idx], samples[idx + 1], samples[idx + 2]
             local brightness = 0.299 * r + 0.587 * g + 0.114 * b
-            local strength = math.min(strength_coeff * (brightness - white_threshold) / (255 - white_threshold), 1.0)
             if brightness > white_threshold then
+                local strength = math.min(strength_coeff * (brightness - white_threshold) / (255 - white_threshold), 1.0)
                 samples[idx]     = math.max(255, r + (255 - r) * strength)
                 samples[idx + 1] = math.max(255, g + (255 - g) * strength)
                 samples[idx + 2] = math.max(255, b + (255 - b) * strength)
diff --git a/thirdparty/libk2pdfopt/CMakeLists.txt b/thirdparty/libk2pdfopt/CMakeLists.txt
index 0287959a7..23912a57b 100644
--- a/thirdparty/libk2pdfopt/CMakeLists.txt
+++ b/thirdparty/libk2pdfopt/CMakeLists.txt
@@ -21,7 +21,7 @@ endif()
 
 external_project(
     DOWNLOAD GIT 59ced371378312d8f332d9a35f5b4a3c33b18954
-    https://github.com/kerivin/libk2pdfopt.git
+    https://github.com/koreader/libk2pdfopt.git
     PATCH_COMMAND ${PATCH_CMD}
     CMAKE_ARGS ${CMAKE_ARGS}
     SOURCE_SUBDIR lib

From ae09a452be4adcd42ff74457cbca22ca0f6ee226 Mon Sep 17 00:00:00 2001
From: keringo <>
Date: Thu, 26 Jun 2025 19:10:02 +0300
Subject: [PATCH 07/15] experiments

---
 thirdparty/libk2pdfopt/CMakeLists.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/thirdparty/libk2pdfopt/CMakeLists.txt b/thirdparty/libk2pdfopt/CMakeLists.txt
index 23912a57b..0287959a7 100644
--- a/thirdparty/libk2pdfopt/CMakeLists.txt
+++ b/thirdparty/libk2pdfopt/CMakeLists.txt
@@ -21,7 +21,7 @@ endif()
 
 external_project(
     DOWNLOAD GIT 59ced371378312d8f332d9a35f5b4a3c33b18954
-    https://github.com/koreader/libk2pdfopt.git
+    https://github.com/kerivin/libk2pdfopt.git
     PATCH_COMMAND ${PATCH_CMD}
     CMAKE_ARGS ${CMAKE_ARGS}
     SOURCE_SUBDIR lib

From 107807351008a6effa61b5580e3bcfb9e0090fa7 Mon Sep 17 00:00:00 2001
From: keringo <>
Date: Thu, 26 Jun 2025 19:13:34 +0300
Subject: [PATCH 08/15] original libk2pdfopt repo

---
 thirdparty/libk2pdfopt/CMakeLists.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/thirdparty/libk2pdfopt/CMakeLists.txt b/thirdparty/libk2pdfopt/CMakeLists.txt
index 0287959a7..23912a57b 100644
--- a/thirdparty/libk2pdfopt/CMakeLists.txt
+++ b/thirdparty/libk2pdfopt/CMakeLists.txt
@@ -21,7 +21,7 @@ endif()
 
 external_project(
     DOWNLOAD GIT 59ced371378312d8f332d9a35f5b4a3c33b18954
-    https://github.com/kerivin/libk2pdfopt.git
+    https://github.com/koreader/libk2pdfopt.git
     PATCH_COMMAND ${PATCH_CMD}
     CMAKE_ARGS ${CMAKE_ARGS}
     SOURCE_SUBDIR lib

From 0a006a6f28f351896c48dca01407f8fab8241809 Mon Sep 17 00:00:00 2001
From: keringo <>
Date: Thu, 26 Jun 2025 19:18:29 +0300
Subject: [PATCH 09/15] constructor args order fix

---
 ffi/drawcontext.lua | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/ffi/drawcontext.lua b/ffi/drawcontext.lua
index 26791d302..14a9d8abc 100644
--- a/ffi/drawcontext.lua
+++ b/ffi/drawcontext.lua
@@ -37,7 +37,7 @@ function DC_mt.__index:getWhiteThreshold() return self.white_threshold end
 local dctype = ffi.metatype("DrawContext", DC_mt)
 
 function DC.new(rotate, zoom, x, y, gamma, white_threshold)
-	return dctype(rotate or 0, zoom or 1.0, gamma or -1.0, x or 0, y or 0, white_threshold or 255)
+	return dctype(rotate or 0, zoom or 1.0, gamma or -1.0, white_threshold or 255, x or 0, y or 0)
 end
 
 return DC

From b7bea8465086f64c0d254f6aa7cde3dc77561ed5 Mon Sep 17 00:00:00 2001
From: keringo <>
Date: Thu, 26 Jun 2025 23:33:20 +0300
Subject: [PATCH 10/15] apply threshold only if white < 255

---
 ffi/mupdf.lua | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/ffi/mupdf.lua b/ffi/mupdf.lua
index 162cd3d6f..baaf15419 100644
--- a/ffi/mupdf.lua
+++ b/ffi/mupdf.lua
@@ -649,7 +649,7 @@ local function run_page(page, pixmap, ctm)
 end
 
 local function apply_white_threshold(bytes_per_pixel, samples, pixel_count, white_threshold)
-    local strength_coeff = 4
+    local strength_coeff = 0.2
     if bytes_per_pixel == 4 then
         for i = 0, pixel_count - 1 do
             local idx = i * bytes_per_pixel
@@ -711,8 +711,10 @@ function page_mt.__index:draw_new(draw_context, width, height, offset_x, offset_
     if pix == nil then merror(self.ctx, "cannot allocate pixmap") end
 
     run_page(self, pix, ctm)
-    apply_white_threshold(self.doc.color and 4 or 1, samples, width * height, draw_context.white_threshold)
 
+    if draw_context.white_threshold < 255 then
+        apply_white_threshold(self.doc.color and 4 or 1, samples, width * height, draw_context.white_threshold)
+    end
     if draw_context.gamma >= 0.0 then
         M.fz_gamma_pixmap(self.ctx, pix, draw_context.gamma)
     end

From 11f85e47a47ebbce34ca6474dc9fd70b5b6cc607 Mon Sep 17 00:00:00 2001
From: keringo <>
Date: Mon, 30 Jun 2025 13:29:01 +0300
Subject: [PATCH 11/15] removed attempt to increase brightness of pixels above
 white threshold without making everything pure white

---
 ffi/mupdf.lua | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/ffi/mupdf.lua b/ffi/mupdf.lua
index baaf15419..b19243c4b 100644
--- a/ffi/mupdf.lua
+++ b/ffi/mupdf.lua
@@ -649,25 +649,22 @@ local function run_page(page, pixmap, ctm)
 end
 
 local function apply_white_threshold(bytes_per_pixel, samples, pixel_count, white_threshold)
-    local strength_coeff = 0.2
     if bytes_per_pixel == 4 then
         for i = 0, pixel_count - 1 do
             local idx = i * bytes_per_pixel
             local r, g, b = samples[idx], samples[idx + 1], samples[idx + 2]
             local brightness = 0.299 * r + 0.587 * g + 0.114 * b
             if brightness > white_threshold then
-                local strength = math.min(strength_coeff * (brightness - white_threshold) / (255 - white_threshold), 1.0)
-                samples[idx]     = math.max(255, r + (255 - r) * strength)
-                samples[idx + 1] = math.max(255, g + (255 - g) * strength)
-                samples[idx + 2] = math.max(255, b + (255 - b) * strength)
+                samples[idx]     = 255
+                samples[idx + 1] = 255
+                samples[idx + 2] = 255
             end
         end
     else
         for i = 0, pixel_count - 1 do
             local brightness = samples[i]
             if brightness > white_threshold then
-                local strength = math.min(strength_coeff * (brightness - white_threshold) / (255 - white_threshold), 1.0)
-                samples[i] = math.max(255, brightness + (255 - brightness) * strength)
+                samples[i] = 255
             end
         end
     end

From be7bbd1f69b61313aadac7bfe5273de0581f8378 Mon Sep 17 00:00:00 2001
From: kerivin <kerivin.zero@gmail.com>
Date: Mon, 4 Aug 2025 19:49:31 +0300
Subject: [PATCH 12/15] paint_white for libk2pdfopt

---
 ffi/koptcontext.lua | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/ffi/koptcontext.lua b/ffi/koptcontext.lua
index 83c495ec5..5dbe5478c 100644
--- a/ffi/koptcontext.lua
+++ b/ffi/koptcontext.lua
@@ -179,6 +179,8 @@ end
 function KOPTContext_mt.__index:setTrim(trim) self.trim = trim end
 function KOPTContext_mt.__index:setWrap(wrap) self.wrap = wrap end
 function KOPTContext_mt.__index:setWhite(white) self.white = white end
+
+function KOPTContext_mt.__index:setPaintWhite(paint_white) self.paint_white = paint_white end
 function KOPTContext_mt.__index:setIndent(indent) self.indent = indent end
 function KOPTContext_mt.__index:setRotate(rotate) self.rotate = rotate end
 function KOPTContext_mt.__index:setColumns(columns) self.columns = columns end
@@ -599,6 +601,7 @@ function KOPTContext.new()
     kc.trim = 1
     kc.wrap = 1
     kc.white = -1
+    kc.paint_white = 0
     kc.indent = 1
     kc.rotate = 0
     kc.columns = 2
@@ -669,6 +672,7 @@ function KOPTContext.totable(kc)
     context.trim = kc.trim
     context.wrap = kc.wrap
     context.white = kc.white
+    context.paint_white = kc.paint_white
     context.indent = kc.indent
     context.rotate = kc.rotate
     context.columns = kc.columns
@@ -739,6 +743,7 @@ function KOPTContext.fromtable(context)
     kc.trim = context.trim
     kc.wrap = context.wrap
     kc.white = context.white
+    kc.paint_white = context.paint_white
     kc.indent = context.indent
     kc.rotate = context.rotate
     kc.columns = context.columns

From 9ad230e6d63a25395f58642eee8f5af380fc660a Mon Sep 17 00:00:00 2001
From: kerivin <kerivin.zero@gmail.com>
Date: Mon, 4 Aug 2025 20:03:14 +0300
Subject: [PATCH 13/15] libk2pdfopt commit hash update

---
 thirdparty/libk2pdfopt/CMakeLists.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/thirdparty/libk2pdfopt/CMakeLists.txt b/thirdparty/libk2pdfopt/CMakeLists.txt
index 23912a57b..80d7d2e31 100644
--- a/thirdparty/libk2pdfopt/CMakeLists.txt
+++ b/thirdparty/libk2pdfopt/CMakeLists.txt
@@ -20,7 +20,7 @@ if(NOT MONOLIBTIC)
 endif()
 
 external_project(
-    DOWNLOAD GIT 59ced371378312d8f332d9a35f5b4a3c33b18954
+    DOWNLOAD GIT df18dfb0b7e33c001f1133c8b3c139b04f0e0a05
     https://github.com/koreader/libk2pdfopt.git
     PATCH_COMMAND ${PATCH_CMD}
     CMAKE_ARGS ${CMAKE_ARGS}

From 98f7a0b73033766878ae2ba961d32094bf1bc49a Mon Sep 17 00:00:00 2001
From: kerivin <kerivin.zero@gmail.com>
Date: Mon, 4 Aug 2025 20:07:51 +0300
Subject: [PATCH 14/15] removed random new line

---
 ffi/koptcontext.lua | 1 -
 1 file changed, 1 deletion(-)

diff --git a/ffi/koptcontext.lua b/ffi/koptcontext.lua
index 5dbe5478c..4d9c497cb 100644
--- a/ffi/koptcontext.lua
+++ b/ffi/koptcontext.lua
@@ -179,7 +179,6 @@ end
 function KOPTContext_mt.__index:setTrim(trim) self.trim = trim end
 function KOPTContext_mt.__index:setWrap(wrap) self.wrap = wrap end
 function KOPTContext_mt.__index:setWhite(white) self.white = white end
-
 function KOPTContext_mt.__index:setPaintWhite(paint_white) self.paint_white = paint_white end
 function KOPTContext_mt.__index:setIndent(indent) self.indent = indent end
 function KOPTContext_mt.__index:setRotate(rotate) self.rotate = rotate end

From 199c8610684de0f51dbcc1f7ed38f8f8dad1b7db Mon Sep 17 00:00:00 2001
From: kerivin <kerivin.zero@gmail.com>
Date: Mon, 4 Aug 2025 20:11:24 +0300
Subject: [PATCH 15/15] added paint_white to koptcontext_h.lua

---
 ffi/koptcontext_h.lua | 1 +
 1 file changed, 1 insertion(+)

diff --git a/ffi/koptcontext_h.lua b/ffi/koptcontext_h.lua
index 3e5b33de0..cc7ecd681 100644
--- a/ffi/koptcontext_h.lua
+++ b/ffi/koptcontext_h.lua
@@ -110,6 +110,7 @@ struct KOPTContext {
   int trim;
   int wrap;
   int white;
+  int paint_white;
   int indent;
   int rotate;
   int columns;