PNG in AZW?

[AlanHK]

I have an epub2 with some png images. I used Sigils's kindlegen plugin (i.e., running Amazon's program) to make an AZW (not including mobi/kf7).

Looking at the resulting AZW in calibre's viewer, it indicates the images have been converted to either gif or jpegs, with some loss of quality and larger size.

So does AZW just not support PNG? I searched for a while, but I couldn't find a definitive statement.
I'm holding out a faint hope that it's an option but not default. A bit pathetic if Amazon doesn't support png 20 years after it was released.

Otherwise, back to making gifs.

[Doitsu]

Originally Posted by AlanHK

So does AZW just not support PNG? I searched for a while, but I couldn't find a definitive statement.

Kindlegen does support .png images, but will convert them if their size exceeds 64-128KB. For details see this related thread.

As jhowell has correctly pointed out, KindleGen does NOT support .png files and will convert them regardless of the file size.

(BTW, you might be able to reduce the file size of your image files with Toxaris's ePub Optimizer.)

[AlanHK]

Originally Posted by Doitsu

Kindlegen does support .png images, but will convert them if their size exceeds 64-128KB.

Hmm. All of my pngs were converted, to gif, or jpeg. None were larger than 13 kB. One png was 3409 bytes, converted to an 8.8kB jpeg.

I used kindlegen plugin, set to make AZW only.
Also tried Kindle previewer, same result with the images.

This all using Kindlegen 2.9

Made another test file with a bunch of PNG, all were converted to jpeg or gif.

I optimise my images with Irfanview, which also lets you target sizes (for jpegs anyway).

[jhowell]

I believe that since the original MOBI format only supports images in GIF, BMP and JPEG formats that kindlegen will convert other formats for backward compatibility with older Kindles.

[AlanHK]

Originally Posted by jhowell

I believe that since the original MOBI format only supports images in GIF, BMP and JPEG formats that kindlegen will convert other formats for backward compatibility with older Kindles.

I was making pure AZW, not mobi or hybrid.
It's all incompatible with old Kindles.

[AlanHK]

Originally Posted by Doitsu

As jhowell has correctly pointed out, KindleGen does NOT support .png files and will convert them regardless of the file size.

That does appear to be the case.
But we only know this from "I believe "? Suck-it-and-see? There really isn't any spec?

I had thought that, aside from the cover, that azw3 was just epub in drag.
But it looks like Amazon chose to screw it up in at least this way.

So, back to the 80s and Compuserve gif for diagrams then.

[DaleDe]

Originally Posted by AlanHK

That does appear to be the case.
But we only know this from "I believe "? Suck-it-and-see? There really isn't any spec?

I had thought that, aside from the cover, that azw3 was just epub in drag.
But it looks like Amazon chose to screw it up in at least this way.

So, back to the 80s and Compuserve gif for diagrams then.

Well at least the patent has expired. Gif is still a good format for diagrams and drawings. Simple and easy to use with good compression.

Dale

[kovidgoyal]

IIRC both mobi and azw3 support PNG images. Various older kindle renderers have issues with some PNG images, which is probably why kindlegen doesn't support them. You can use PNG images even in plain MOBI files via an option in the MOBI Output section of the conversion dialog in calibre.

[AlanHK]

Originally Posted by kovidgoyal

IIRC both mobi and azw3 support PNG images. Various older kindle renderers have issues with some PNG images, which is probably why kindlegen doesn't support them.

I think it very likely that these troublesome "renderers" would be limited to mobi/kf7 anyway, so to enforce this conversion for AZW3 is pretty annoying.

Though since the standard setting is to make a hybrid file with both kf7 and kf8, that would mean duplication of some images (I'm assuming that the images are shared between formats; only the text different, I could well be wrong). I'm currently just doing some books to load on my own Kindle. I do occasionally code books for publishing though, so I need to follow the standards Amazon set, implicitly or otherwise.

Many ebook designers do use png in making epubs, then just convert using kindlegen. And their images are silently degraded.

[HarryT]

Originally Posted by AlanHK

I'm assuming that the images are shared between formats; only the text different, I could well be wrong

An easy thing to experimentally test. Add, say, a 100k JPEG file to your ePub book and then re-convert it. If the images are shared between Mobi7 and KF8, the size of the resulting Mobi file will increase by 100k; if it's not shared, it'll increase by 200k.