Quote:
Originally Posted by AlanHK
That prodded me to use KindleUnpack rather then Calibre's viewer to extract the files.
And you're right: in the unpacked files the map is named as a jpeg, but is actually a gif 6 bytes larger than the source. (Using IrfanView to get the specs.)
-- I think you'll find that is also really a GIF.
So, sorry about that. I had the habit of using Calibre's ebook viewer to check out conversions, but it seems my assumption that it just unpacked and then viewed the file was wrong.
The reason I was checking this out is that the AZW was rather smaller than the epub, when it's usually the other way.
So I looked at the other unpacked AZW images, and found that while the gif was the same, for some jpegs compression had been changed.
e.g.
In the ePub -- 87 kB, quality 98
in the AZW -- 42 kB, quality 80.
The cover image though was the same spec, same size, quality still 98.
So, unless I've made another dumb assumption, it looks like Kindlegen does leave GIFs as-is, and (always?) cover images, but other jpegs may recompress.
And I found earlier that PNGs are converted to either GIFs or JPEGs, which is why I started to use GIFs rather than PNG for most diagrams and maps to keep them sharp.
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I have noticed that when I convert my home-rolled ePubs with Kindle Previewer, the JPEGs are most definitely being compressed further! Greyscale images where I have carefully cleaned up the backgrounds to pure white will, after conversion, and viewed on a tablet in the Kindle app, show annoying grey speckles in what *should* be a pure white background. Said images are also considerably softer looking than they should be.
Whereas the ePub retains the image quality, and backgrounds remain pure white even with max brightness set on either my iPad Pro or Pixel C tablets. And images remain sharp and crisp!
If anyone knows a way to prevent the rather profound loss of image quality when converting to Kindle dual mobi format, I would love to know about it!
The difference is pretty sad really, and can easily be noticed between my Kobo Aura ONE and Kindle Voyage as well as on the tablets.
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