[Hitch]

Originally Posted by photon_man62

Amazon adds extra JPG compression to images in KF8 files. So in this example, a cookbook which used to take up 62MB (because of all the photos of ingredients, recipes etc.) in the "classic MOBI" format now takes up only 14MB as a KF8 file. The same cookbook still takes up 62MB in other ebook stores that use EPUB.

Yes, naturally. Images inside a MOBI are compressed to meet certain size stipulations, and always have been. With the advent of the newer devices, the size restrictions are easing up a bit, but still...for most of the MOBI life, each image has been compressed to 128kb.

In the link I posted, I gave an example of the same pictures from an EPUB (mouse out) and from a KF8 file (mouse over the photo). The compression isn't very bad so you normally don't see a big difference in image quality.

Presumably, that works with what, pop-ups? I'm not seeing anything on mouse-over at all, on Chrome, Win7. I have a pop-up blocker, so if that's what happens...if it's supposed to be doing something else, I'm not seeing it. But I've seen thousands of books, so I don't need to see your examples. Yes: there's a difference, because ePUB basically allows someone to "go wild" with image sizes if they wish (although, older devices can choke on HTML files that are larger than about 256KB, if memory serves; don't know how they manage enormous images, assuming that they do.) That's been a restriction of working with MOBI for years now.

However when you look closely, you will see that there is a difference. Hold down Ctrl and press + a few times to zoom in. It's easiest to notice in picture #2 if you look at the background. When you mouse over the image you will immediately see that there is a completely different background texture. Look, this is the top-left corner of picture #2:

<snipped for the forum width>

The difference in picture quality isn't really a problem during normal viewing, especially on a black&white e-ink reader. However if the ebook you're publishing is very reliant on pictures, you should still keep this in mind.

I wasn't asking you about mobi and ePUB--if you look at my post, I asked you why you thought that the KF8 mobi was smaller than "the classic mobi," by which I assume you mean the KF7 mobi. Even with KFX format, I believe, the "multi-MOBI" (the file that contains the source, the KF7, the KF8 and possibly the KFX files) stores hi-rez and low-rez images, the former for the KF8 and KFX files, and the latter for the KF7 mobi.

Presumably, the "classic mobi" would then be smaller than the KF8--would it not?

Or am I missing something else from your posts?

Anyway: if one is working for a MOBI, it's wise to try to pre-process your images, using the best compression algorithms you have or can find. We do a lot of this--we have a lot of clients with image-heavy books (we've done some with just shy of 1,000 images). We use a set of compression tools (basically, File Optimizer), and that works fairly well to get most images to the point where the Amazon compression algo won't kick in.

Amazon no longer mentions the max size for a single image, but I think that the 128 shifted up to 256, a year or so ago. (Anyone else here remember?). In any event, if you place very large images into an ePUB for MOBI conversion, without some pre-processing, yes...you'll get an unexpected compression.

But I'm still fairly certain that a KF8 file is larger than the PRC/MOBI file. Of course, I could be wrong. It's certainly happened. ;-)

Hitch