As a follow-up to the "comic" book type, this OPF property doesn't seem to work with region magnification of text. With this book type, magnification of text is screwed up on the Kindle Paperwhite. Also with the "comic" book type, background images must always be coded using the background-image CSS property, otherwise pictures and text fall apart on the Kindle Paperwhite.
With the "children" book type, text magnification works fine on all devices, but quality of pictures is reduced to under 256KB. With this book type, one can use HTML img tags for background images (not a good idea, but the official chidren's book sample employs this approach).
Damned if you do, damned if you don't. It's a shame file sizes are restricted and delivery charges vary. jpg images compressed at 100% progressive would look great in all devices at all times and would still be about five times smaller than tiffs and bitmaps. EBooks on the web seem to be at that stage where mp3 files were ten years ago where you did your best to make them sound good at only 64k, but they never really did until bandwidth increased and larger file sizes became the norm.
Hey, it worked! I must have been trying it as you were typing that message. My initial images (I used three of them) were all shot with a digital camera at 1600 x 1208. (I didn't bother cropping them or trying any different dimensions in this test.) The cam shoots uncompressed jpgs (okay jpgs are never really uncompressed, so let's just say they were compressed at 100%.) I brought them into Ulead PhotoImpact and compressed them at 75%. Their file sizes then were as follows:
pic 1 - 222Kb
pic 2 - 321Kb
pic 3 - 259Kb
I put them all on one HTML page with Test Pic 1, 2, and 3 written above them and nothing else and centered everything. After putting the HTML (I didn't make an OPF or NCX) through KindleGen Previewer, and then tearing the resulting mobi file apart with mobi_unpack, I found that KindleGen had further compressed the files to the following:
pic 1 - 117Kb
pic 2 - 124Kb
pic 3 - 121Kb
I took the OPF file that KindleGen made automatically and added the metadata tag:
<meta name="book-type" content="comic"/>
I also changed the names of the image files back to their original names (you know how KindleGen changes names of files all the time) and replaced the newly compressed image files with the original ones and ran the OPF through KindleGen.
This time after tearing the new mobi apart, I found that KindleGen didn't compress the photos at all!
It still needs some testing, and of course a large HTML file with a LOT of photos will probably result in KindleGen's compressing them further as per this statement in the Guidelines (which I'm afraid may apply to reflowable books too using this process):
"For fixed-layout books and comic books, KindleGen reduces the quality factor of the image, but not the resolution. If the image cannot be scaled down to meet the size limits by reducing quality factor up to 40%, KindleGen fails the conversion process."
But at any rate, it looks as though we may now have a way to beat the 127Kb maximum for reflowable books as long as there aren't too many photos in them.
Edited to say the obvious: If this works with reflowable books, then it will likely work with children's books too.
Hey, nice hack! I tried myself and this is what I found:
with KindleGen 2.7, this approach cracks the 127KB limit for images in reflowable books
this method does not work with KindleGen 1.x
the limit on images is smaller than 800KB, probably 256KB because a 650KB image was downsized to 220KB
if a book contains over a hundred images, the results (final book size) are very close to regular reflowable books
As far as fixed layout is concerned I would say that the "comic" book type has much more bugs than the "children" book type. Region magnification both for text and pictures is screwed up on the Paperwhite and possibly on other non-Fire devices. This problem is especially evident in the official comic book sample (magnification of incorrect part of a page). In my templates (Paperwhite mode) the "comic" book type causes the magnified popup box to expand to the full-screen view, both for text and images.
I've read through the thread, but there doesn't appear to be a clear solution. It seems to me that there are now at least three Kindle Fire screen resolutions and at least two sets of proportions. In terms of trying to future-proof my files it would be really useful to work to the optimum requirements (Kindle Fire HD8.9), but at the same time ensure legacy compatibility.
I think I have downloaded the most up-to-date version of the publishing guidelines (2012.5), but there doesn't appear to be any mention of the HD or the HD8.9 in the fixed layout section. I understand that there are cost implications relating to larger file sizes, but these will probably change over time. I think that I'd be tempted to have a file that's 50% larger than the HD8.9 requires even although this is below the spec recommended by Amazon (100% larger).
Anyone have a view on whether the screen proportions of the HD will prevail over the original screens proportions? That would be useful to know, as then we could make a call on which proportions to use.
This problem is reproducible on my Paperwhite, although with regular Kindle books the real Paperwhite and the Previewer emulation do not always match. For example, in the emulation, the contents of the NCX file are not added to the "Go to" menu.
My advice is to not worry about future proofing (let Amazon worry about that). I don't have a Fire HD and HD 8.9", but those who do say that 600 x 1024 fixed layout works fine there (full screen pages). If you make your picture files 1125 x 1920, you will unnecessarily increase the file size and reduce your royalties (because of higher delivery costs). You may also end up with a file that cannot be uploaded to KDP (50MB limit). Finally, there is no guarantee that the scaled up version will work as expected on all devices that support fixed layout (Amazon software and firmware occasionally have bugs): a "Kindle" manufactured after August 2012, Kindle Paperwhite, Kindle Fire, Kindle Cloud Reader, Kindle for iPad, and Kindle for Android (the tablet). If you don't want surprises, stick with the standard 600 x 1024 pixels for the pages (you can make the cover bigger if you want).