fix color autocontrast (#1026)

kindlecomicconverter/comic2ebook.py

@@ -639,8 +639,8 @@ def imgFileProcessing(work):
         workImg = image.ComicPageParser((dirpath, afile), opt)
         for i in workImg.payload:
             img = image.ComicPage(opt, *i)
-            is_not_color = not opt.forcecolor or not img.color
-            if is_not_color:
+            is_output_grayscale = not opt.forcecolor or not img.color
+            if is_output_grayscale:
                 img.convertToGrayscale()
             if opt.cropping == 2 and not opt.webtoon:
                 img.cropPageNumber(opt.croppingp, opt.croppingm)
@@ -649,11 +649,10 @@ def imgFileProcessing(work):
             if opt.interpanelcrop > 0:
                 img.cropInterPanelEmptySections("horizontal" if opt.interpanelcrop == 1 else "both")
             img.gammaCorrectImage()
-            if is_not_color:
-                img.autocontrastImage()
+            img.autocontrastImage()
             img.resizeImage()
             img.optimizeForDisplay(opt.reducerainbow)
-            if is_not_color and opt.forcepng:
+            if is_output_grayscale and opt.forcepng:
                 img.quantizeImage()
             output.append(img.saveToDir())
         return output

kindlecomicconverter/image.py

@@ -353,9 +353,7 @@ class ComicPage:
             self.image = Image.eval(self.image, lambda a: int(255 * (a / 255.) ** gamma))
 
     def autocontrastImage(self):
-        # autocontrast on non grayscale images has unexpected results 
-        # since it autocontrasts each color channel separately
-        self.image = ImageOps.autocontrast(self.image)
+        self.image = ImageOps.autocontrast(self.image, preserve_tone=True)
 
     def convertToGrayscale(self):
         self.image = self.image.convert('L')