05-17-2026, 01:00 PM
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#1 |
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Grand Sorcerer
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Join Date: Apr 2011
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amazon EPUB, KF8 comparisons
As part of comparing amazon supplied EPUB amazon supplied KF8/azw3, I bought a couple of Brandon Sanderson books, first Tress ..., then Lost Metal ..., based on posts in the thread https://www.mobileread.com/forums/sh...d.php?t=311429 . I don't read KFX, someone else will have to make comparisons for that,
The rest of this post will be about what I have learned so far, followed by a post specific to Tress ..., followed by a post specific to Lost Metal .... amazon's image strategy seems to be heavy handed and simple minded. If the image is a PNG, it gets converted to JPEG, even if GIF would be better and regardless of whether kindles can display that specific PNG format in a KF8/azw3 ebook. I am pretty sure that years ago I was able to use kindlegen to convert an EPUB with PNG images to azw3 that KindleUnpacked to an EPUB with PNG if the PNG was 8 bit grayscale. I don't remeber whether any color PNG worked, but very annoyingly 4bit grayscale did not work. If any image is more than about 120 KB, its size in pixels gets reduced and get compressed as a JPEG, I'm guessing with some fixed quality setting. There might be some maximum dimension limit, but quite large images will get passed through unchanged if they are less than 120 KB or so. (If an image size in bytes is not evenly divisible by 4, amazon will append null bytes until it is. I count that as unchanged.) Tress ... has a 91320 byte 2179x1835 JPEG in both the amazon supplied EPUB and the amazon supplied azw3. If two images over 120 KB have the same dimensions but different sizes, the dimensions will be reduced differently. That spoils displaying images meant to se hown on facing pages or joining them into a single image. More about that in the Lost Metal ... post. I don't know the precise threshold for image size reduction, maybe it is al large as, say, 128KB. It is already known that amazon EPUBs don't have the <dc:creator> (author) tag and all the book text XHTML files have no line terminators. |
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05-17-2026, 01:04 PM
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#2 |
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Grand Sorcerer
Posts: 6,009
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Join Date: Apr 2011
Device: pb360
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Tress
I haven't read Tress ... or any other book by Brandon Sanderson (maybe someday). This post is strictly about differences in production value and technical details between the amazon supplied EPUB images and the amazon supplied KF8 images. I forget when amazon dropped color from KF8 images, but Tress ... KF8 images have color.
It turns out that most of the images in Tress ... are very robust angainst amazon mangling despite being quite a bit above average in number of pixels. I think this is mainly due to their nature and the care in their design and production with an eye toward being very compressible. The images are mostly GIF with limited pallette and very smooth coloring. The only GIF that doesn't get passed unchanged is the title page, which gets shrunk from 1201x1803 to 942x1414 and converted to JPEG. This is a good place to mention that after the list of illustrations in the table of contents is a QR code containing a URL which has 16 webp images that have higher resolution than the EPUB images. For example, the title page is 1318x2048, but uniquely is also a fancier style. Just as the amazon EPUB images aren't much higher resolution than the KF* images, the rest of the webp images aren't much higher resolution than the amazon EPUB images. But the webp images are significantly higher resolution than the KF8 images. The KF8 images look OK to me on a 6" 300 DPI e-ink kindle and unzoomed on a computer monitor. The EPUB images are better, but for me, not compellingly so. I think this is because of the skill and effort put into making the originals such high quality and smooth in spatial and color detail. So this is not the typical kindle book with images that really suffer from going through the meat grinder. Lost Metal ... is another story. The dimensions and size information for the amazon EPUB and KF8 images are included inline below and attached as TressEPUBimages.txt and TressKF8images.txt Tress ... amazon EPUB images details: Spoiler:
Tress ... amazon KF8 images details: Spoiler:
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05-17-2026, 01:11 PM
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#3 |
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Grand Sorcerer
Posts: 6,009
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Join Date: Apr 2011
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Lost Metal
Lost Metal ... by Brandon Sanderson has a number of images with characteristics of images that I think require higher resolution than typically present in ebooks from amazon. Examples include maps and partial newspaper pages. Note that I have also used kindlgen to convert the EPUB to azw3 for viewing on a 7" Oasis, which preserves the images. I have not found a QRcode or URL in the book pointing to even higher resolution images on the author's web site.
I've always been frustrated by maps in KF*/azw3 mostly being between barely legible to quite illegible even when zoomed. Usually they are seriously degraded by some combination of poor source contrast, poor scan quality, and insufficient resolution. The low contrast of eink really requires higher image contrast than a conventional computer screen or even paper. I am almost never able to get much use from a map in an azw3 book. In Lost Metal ... the Elendel Basin map is: amazon epub image-0-4.gif 1600x2493 801,973 bytes amazon azw3 image00367.jpeg 615x958 108,432 bytes On a 7" Oasis, the EPUB map is significantly better than the one in the azw3, but the azw3 is suprisingly legible. Only the legend in the upper left corner is pretty much unreadable. This is particularly surprising because of all the fine detail such as the depth contours and non-text, non road markings, which also seem to mask any JPEG artifacts. An exception is the symbols on the lat lon like grid, which are pretty much obliterated by the combination of shrinking and JPEG artifacts. I don't know how much that harms the usefulness of the map since I haven't read the book. The Elendel city map amazon epub image-0-5.gif 2316x1725 1,057,610 bytes amazon azw3 image00368.jpeg 777x579 108,432 bytes amazon azw6 HDimage00006.wdp 777x579 70,369 bytes did not fare nearly so well, partly because of the fine detail showing the (unlabeld) minor roads and streets, which mostly become text abscuring clutter in he shrunk from GIF JPEG. The grid labels are single (very small) letters and digits, which look nice and clear on the EPUB GIF shown on a computer monitor, barely legible to me tap zoomed to full screen in landscape mode on a 7" Oasis, and clean and easy to read when pinch zoomed on the Oasis. The amazon supplied azw3 JPEG version is challenging unzoomed on a computer monitor. For me, it is unusable unzoomed on the Oasis, almost usable zoomed to full screen, and barely usable but eye watering when pinch zoomed. The grid labels were really bad, even zoomed, but not as bad as the symbols on the Elendel Basin map. This is better than I expected when I first saw the map, but this image is essentially ruined by the excessive shrinking and GIF to JPEG conversion. The Map of the Basin and the Southern Continent amazon epub image-0-6.gif 1600x2493 802,206 bytes amazon azw3 image00369.jpeg 656x1022 108,688 bytes amazon azw6 HDimage00007.wdp 656x1022 69,488 bytes text is mostly too small for me to read on a 7" Oasis until I tap zoom to full screen for both the converted tp azw3 EPUB and the amazon supplied azw3. But this might be a limitation of my eyesight. The EPUB version is very comfortable to read on a computer monitor, but I need to take my glasses off and get close to the screen for the amazon supplied azw3 version unless I double the resolution. But then the JPEG artifacts get obtrusive and everything looks somewhat fuzzy. Note that all three EPUB maps are a bit smaller than a Scribe screens. Scribe owners should be particularly that the EPUB version is available for this book. The only other images worth comparing are the four newspaper partial pages, which will be discussed as a group. amazon epub image-0-10.gif 1600x2300 620,135 amazon azw3 image00373.jpeg 606x872 119,852 amazon azw6 HDimage00011.wdp 606x872 76,875 amazon epub image-0-28.gif 1600x2300 591,215 amazon azw3 image00391.jpeg 630x906 119,700 amazon azw6 HDimage00011.wdp 630x906 76,548 amazon epub image-0-37.gif 1600x2300 438,181 amazon azw3 image00400.jpeg 586x843 120,792 amazon epub image-0-55.gif 1600x2300 627,969 amazon azw3 image00418.jpeg 616x885 119,332 The newspaper images from the EPUB are all very clean GIFs that look very good on a computer monitor and very sharp and even readable unzoomed on a 7" Oasis screen. (But the text is very tiny.) After zooming they are still sharp and clean and panning is very smooth on the Oasis. The pictures and drawings look a lot like newspaper halftone, but actually use some sort of dithering pattern optimized for GIF compression. Each of the newspaper images are followed by reflowable text with the content or each article in the image, so it isn't necessary to be able to read the text in the image. They look to be two pairs of facing pages (with a column 100 pixels wide common to each image in a pair). Letters in even the smallest font have lots of fully black pixels. That, combined with the full white artifact free background, result in sharp, good contrast text on an e-ink screen. The newspaper images from the amazon supplied azw3 are all JPEG reduced by a factor of approximately 2.6, with the actual factor different for each dimension and each image, combining two of the images would not be as trivial as for a pair of the GIFs which are all 1600x2300. Unzoomed on a computer monitor, the text is fuzzier and grayer than the text in the GIFs, the latter because the text has been shrunk so thin that there are few fully black pixels. It actually is readable by me by getting very close, but it is not at all easy on my eyes. JPEG artifacts are not directly visible to me. Zooming to 200% makes the text much more comfortable to read but is a bit fuzzy and JPEG artifacts are numerous even in the white background. Surprising to me, the text is (barely) readable unzoomed on a 7" Oasis, but the fuzziness and grayness combined with the not great contrast of e-ink don't help. Zooming helps and the Oasis handles panning the zoomed image well, as would be expected since the image is much smaller than the GIF, which also panned reasonably smoothly. (This is on e-ink after all.) The pseudo halftone look is lost in the reduced size JPEG newspaper images. The dimensions and size information for the amazon EPUB and KF8 images are included inline below and attached as LostMetalEPUBimages.txt and LostMetalKF8images.txt Lost Metal amazon EPUB images details: Spoiler:
Lost Metal amazon KF8 images details: Spoiler:
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05-17-2026, 01:12 PM
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#4 |
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Grand Sorcerer
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Reserved.
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05-17-2026, 02:00 PM
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#5 |
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Resident Curmudgeon
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That is an excellent comparison. Why is Amazon monkeying around with the images so that they can be so bad?
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