Save images in GIF when output is set to MOBI and forcepng is used (#981)

* Save images in GIF when output is set to MOBI and forcepng option is used

* Save images in GIF when output is set to EPUB, kindle profile is used and forcepng option is set

* media-type="image/gif"

---------

Co-authored-by: Alex Xu <alexkurosakimh3@gmail.com>

kindlecomicconverter/comic2ebook.py

@@ -336,6 +336,8 @@ def buildOPF(dstdir, title, filelist, cover=None):
                 ".xhtml\" media-type=\"application/xhtml+xml\"/>\n")
         if '.png' == filename[1]:
             mt = 'image/png'
+        elif '.gif' == filename[1]:
+            mt = 'image/gif'
         else:
             mt = 'image/jpeg'
         f.write("<item id=\"img_" + str(uniqueid) + "\" href=\"" + folder + "/" + path[1] + "\" media-type=\"" +

kindlecomicconverter/image.py

@@ -325,8 +325,12 @@ class ComicPage:
     def save_with_codec(self, image, targetPath):
         if self.opt.forcepng:
             image.info["transparency"] = None
-            targetPath += '.png'
-            image.save(targetPath, 'PNG', optimize=1)
+            if self.opt.iskindle and ('MOBI' in self.opt.format or 'EPUB' in self.opt.format):
+                targetPath += '.gif'
+                image.save(targetPath, 'GIF', optimize=1, interlace=False)
+            else:
+                targetPath += '.png'
+                image.save(targetPath, 'PNG', optimize=1)
         else:
             targetPath += '.jpg'
             if self.opt.mozjpeg: