Maximum Image Size in Apple Books

  1. 3 years ago

    I'm building a fixed layout childrens' book in Pubcoder for export to EPUB, using an iPad page format of 1024 x 768 pixels.

    I have two Pubcoder files that are identical except for the images used.

    File A has jpeg images sized to 3072 x 2360 pixels (7,249,920 pixels). These scale to fit the width (1024px) of the stage perfectly. Their height when scaled is slightly more than that of the stage (768px).

    File B has the same jpeg images as File A, but each image is cropped to exactly 3072 x 2302 (7,077,119 pixels). These scale to fit both the width and the height of the stage perfectly.

    Both files therefore share identical active image dimensions of 3072 x 2302 pixels (7,077,119 pixels).

    But Pubcoder treats the two files differently when exporting to EPUB.

    Pubcoder exports File B to EPUB, at 3x pixel density, without any warnings.

    Pubcoder warns that File A, at 3x pixel density, has images that exceed the maximum 4 million pixels permitted on the Apple Store.

    Pubcoder exports File A to EPUB, at 2x pixel density, without any warnings.

    Given that the active image size in both files is identical (and in excess of 4 million pixels), why does one export successfully to epub at 3x pixel density, and the other not?

    Is this a bug in Pubcoder, or something that I’m not understanding about images?

  2. I'm not sure about the reason for the difference in export behaviour, but I would have thought you would want to resize your images and optimise them for digital display anyway, before putting in your eBook? I also create renditions of 1024 x 768, and my original images are this ratio but larger. I resize them down before embedding - my exported epub files were getting ridiculously large. To the point where the file as a whole was too large to load to the Kobo bookstore. Even if Apple lets us load big files, customers still have to download them. Is there something I'm missing about the way you're embedding images, that this shouldn't be an issue?

  3. Angelo S

    22 Dec 2020 Administrator

    PubCoder has an option in Project Settings → EPUB → Reduce Pixels density to meet iBooks Store picture size limit, that will do what it says.
    Of course this is valid for rendered images only. If you turn on "Use original image" in an image object, it will just use the original file without resizing it. The same happens for some other images, e.g. the ones used in image galleries, or the project cover file. So, it depends on where you are using the image file and the settings of the image objects themselves.

  4. Hi Angelo,

    These are the main background images, one per page.

    I have that option turned on in both files (Project Settings → EPUB → Reduce Pixels density to meet iBooks Store picture size limit).

    And "Use original image" is turned off in both files. So the images are being rendered ... ?

    Should the pixel density setting in the Project panel (1x, 2x, 3x) override the setting to "Reduce Pixels density to meet iBooks Store picture size limit"? Or does it work the other way round?

    Is there any reason, given the same settings, as above, for each file, why Pubcoder would produce a warning for one file and not the other?

    Thanks :)

  5. Hi Kathryn,

    I do indeed want to optimise my images for digital display :) I'm attempting to find the optimum size and resolution to do that. My images, like yours, are the same ratio as 1024x768, but larger.

    When you say

    I resize them down before embedding

    , I'm not sure what you mean. Are you physically changing the dimensions of the source image again, to 1024x768, or just scaling it using Pubcoder's settings for the image object? I mean, are your embedded images actually 1024x768, or some larger multiple of that like 2048x1536 or 3072x2304?

    I get what you mean about ridiculous epub file sizes. I've spent this past week trying to reduce file size while retaining quality. This is not an easy balance. The image can look good at loading, but it's when you zoom in that the quality plummets.

    It's hard to know what a reasonable file size is for an epub. How many megabytes do you think readers are prepared to download? Or do they just go on how long it takes to download?

    Have you found a sweet spot for your embedded image sizes? One that retains image quality when you zoom in but with a reasonable epub file size?

    John :)

  6. Angelo S

    23 Dec 2020 Administrator

    Hi John,

    @John These are the main background images, one per page.

    I have that option turned on in both files (Project Settings → EPUB → Reduce Pixels density to meet iBooks Store picture size limit).

    And "Use original image" is turned off in both files. So the images are being rendered ... ?

    We're missing something :) please send the pubcoder project file here so I can take a look:

    @John Should the pixel density setting in the Project panel (1x, 2x, 3x) override the setting to "Reduce Pixels density to meet iBooks Store picture size limit"? Or does it work the other way round?

    The pixels density is a project setting. The option to reduce it tries to lower it for individual images which would otherwise be more than 4 million pixels with the pixels density project setting.

  7. @John I ask my illustrators to produce my background images at 1024 x 768 size. For images created before I started this, or created for different size books, I size them down to that before embedding. In the past (on Windows OS) I used Irfanview for batch resizing etc, but :-( it's not available for Mac.
    I searched recently for good alternatives (preferably free) and for the moment I am using this online tool:
    Not ideal in the free version because the number you can include in a batch is limited. But even so it took me less than 5 mins to do 72 images in multiple batches.
    I'll probably upgrade to the paid version at some point if I can't find a better free solution. Or just get better at insisting on the required dimensions from my illustrators!
    I notice that in Pubreader I can't zoom in on pages anyway - I'm not sure if that's normal behaviour or not; I've only just tested. In the iOS Books app I can, and yes, the quality deteriorates to poor, but I doubt my readers would zoom. Even when loaded onto my iPad Pro 12 inch (larger screen), I think the image quality is still fine, and I make sure I always use large enough font that they won't need to zoom on that.
    I'm still trying (unsuccessfully) to work through the testing process on my Samsung android tablet for the Android app versions through Google Play and Amazon stores. I don't know if you can Zoom on Android devices. I always thought iOS would be my main platform for the books. But Google analytics on my website says of the 263 unique visitors in the last 30 days, 93 have been on an Android OS, 49 on Windows, 44 on a Mac OS, 27 on iOS and 28 on 'other'. Hence the urgency to prioritise Android versions. File size? Looking at all the apps loaded on my iPad, other than tiny ones, they mostly range anywhere between 40MB and 300MB. Kobo file size limit is 100MB. My 'flat' illustration picture books are around 20MB - 40MB which I figure is absolutely fine. My animated illustration picture books were as much as 160MB before resizing, which I figured was a bit much. After resizing, they sit around 80MB, which I think is still high, but the upper limit of what I'm happy with. I'm no expert, so just sharing for info!

  8. Angelo, I've uploaded the two files (File A and File B).

    Many thanks for your help, as always.


  9. Kathryn,

    thank you for your awesome reply. I'm no expert, either, so every bit of information is helpful. I'm actually blown away by the scope of your work.

    It makes sense to drop your images down to dimensions of 1024x768 if you're not expecting your readers to zoom (why don't you expect them to zoom?). Image quality in the epubs as loaded (not zoomed in) is good. I'm sure they would retain that quality on your iPad Pro. It's just the zooming that creates issues.

    Kobo's not the only retailer with a 100MB limit, and the need to retain some level of quality at zoomed-in views makes 100MB a real hurdle. Mind you, I'm pleased that the epubs I'm creating for the current project are below that limit (though not by much) while delivering okay zoomed-in visuals. Not perfect visuals, but okay.

    I've just checked, and in Pubreader I can't zoom in on pages either. I can't remember if earlier versions of Pubreader used to zoom in or not.

    I need to revisit my Android tablet regarding zoom. I think I could zoom-in in the Kobo app, on a Samsung tablet. I've been focusing first on a version for Apple Books this time round. Android is next up. But if you're creating Android apps (as opposed to epubs), I don't think they would zoom because the Pubcoder apps are basically the Xpub file wrapped in a different shell. And it seems the xpubs don't zoom ...

    You're right that a lot of readers are using Android. I had tracking links set up in a free ebook to see where hits were coming from, and there were big numbers coming from Google Play books. Not as many as I was getting from Kindle apps and devices, but close. But when I delved into the app-creation side of Pubcoder, that was a whole other thing in itself. I built an iOS app (great agony and suffering involved) and stopped. I'm so impressed that you've created apps for both platforms and haven't been driven mad :)

    We've moved in opposite directions, I think. I've come to believe that iOS is the best - perhaps the only - platform for my interactive eBooks, but I actually started designing for Kindle. I hand-coded an interactive edition for Kindle, and it worked, but Kindle only supports little bits of the EPUB3 spec, and does it in proprietary ways; and what I could achieve on that platform could not compare with a proper EPUB3 implementation (via Pubcoder) on iOS. I'm actually thinking of going back to flat-file picture books on the other platforms with, as you say, text big enough to read without zooming. My first picture book was a flat file, and was only about 10MB.

    The interactive books are big files. There's no way round it, I think. And unfortunately, Apple Books doesn't seem to attract the numbers of readers who use the other platforms, like Kindle and Android ... and Kindle devices are just Android devices with Amazon-proprietary limitations built in.

    Again, thanks for sharing so much info. I would love to see what you're working on. Can I buy your books?

    John :)

  10. I agree, iOS is still the best device for interactive eBooks. But from my website analytics, iOS users are a very small part (only about 10%) of my website visitors. Android devices account for over 35%. So...
    I've managed more testing this morning; the bug with Pubreader on my old Android tablet seems to have resolved itself (yay!) so I could test that. Everything works fine - you can't zoom, but I don't want people to zoom anyway, so...
    The Android app versions aren't working - the file sizes with the animations are huge, and the pages are loading really slowly, plus the narration isn't playing.
    So I have an android solution now to offer using Pubreader - good enough for a start. I'll keep working on the Android apps.
    I'm not sure about the rules on this discussion forum regarding self-promo, and don't want to contravene anything. But if you want to look at my website, google 'Reading's a Breeze! dot com' :-)
    Happy to have found a fellow Aussie trying to untangle all these threads of technology!

  11. Hi Kathy,

    It rings such a clear bell when you say "the file sizes with the animations are huge, and the pages are loading really slowly ..." From memory, it's why I abandoned the iOS app that I was experimenting with, also. It was just too big, too clunky and too slow. I can't remember how the read-aloud went.

    It's good news about your Android testing with xpubs and Pubreader. I'm inspired to move on to the Android versions of my book too. Thank you for the heads up re your website. I found it, and I've bought a couple of books to check out. Congratulations on your Interactive Book Award, by the way. I've bought that one :) You really are a powerhouse. And an Aussie one at that! Yay!

    Thank you for sharing so much information. It really helps to be able to discuss this stuff.



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