Hi,
I made a figure on Ai and placed it on Ps as a smart object & exported it to png (Screenshots 1 and 2).
The png looks blurred on EPUB-Apple Books (Screenshot 3).
Is there any way to improve it?
So far, no problem with the work process above.
Hosun
18
Replies
1.
My work process is explained in Screenshot 1:
- I make a figure on Ai and do copy/paste it on Ps as a smart object.
- I go through Ps, because smart object improves the quality of the png.
- Then, I place the png on Id and export it to EPUB.
2.
In Ps, resolution is 150 ppi.
In uploading to Apple Books, there is a limit to each image file (5.6 MN px). It's the reason for 150 ppi.
Converstion Setting on Id is in Screenshot 2.
3.
I tried various ways. But they don't give me a better outcome.
So far, no problem with my work process.
Hosun
If I may be so bold in stating the following: both the question and the answers here need clarifying. 🙂
First, a couple of ground rules must be defined in regard to how InDesign treats images in documents that have a digital platform intent:
- PPI is not important in Illustrator or Photoshop when preparing images for digital output. This includes desktop screens, mobile devices, tablets, and so forth. We work with pixels, not PPI or DPI. Only for print jobs do we deal with PPI/DPI.
- PPI is however important to InDesign because the way InDesign calculates things it "thinks" in PPI even when selecting a digital intent document template. So while the rest of the world disregards PPI for digital bitmap-based imagery, InDesign must use a standard PPI setting to make sense of the size of imported bitmaps.
- InDesign assigns therefore an arbitrary 72 PPI to images that translate 1:1 to the digital document template that a user picked.
- In InDesign all document templates that are listed under Web and Mobile fall in the category of digital intent.
- When the effective PPI of a placed image equals 72PPI that image's resolution matches the device's native resolution one on one 1:1. 1 pixel in your bitmap image matches 1 pixel in the document canvas.
- To publish an epub with bitmap images at 100% native resolution to our main digital target platform we must export our epub at a PPI resolution of 72PPI. (NOT 150PPI. NOT 300PPI !!!)
If this all sounds rather obscure to you, then you find yourself in a right state of mind. 😛
A simple example to explain how this works.
We create a new document meant to be published to regular iPads as the highest quality digital platform. We can still use the produced epub on lower resolution devices, of course (but you have to realize that images may have double the resolution actually required for those displays).
An iPad features a retina screen with a resolution of 2048 by 1536 pixels. InDesign interprets this as 2048px * 1536px @ 72PPI.
When we import an image and place it we should check the effective PPI in the Links panel. If the placed image (after transforming to the required width, height, and cropping) is much lower than 72PPI we have a problem. Ideally it should be 72PPI or higher!
To prepare bitmap images for our iPad output platform, we completely disregard PPI. We ONLY look at the pixels involved:
- If we require a full width image in portrait mode: in Photoshop (or equivalent image editor) the resolution should be a minimum of 1436px.
- If we require a full screen image in a landscape page: 2048px by 1536px.
- If we require a quarter width image at landscape resolution: 1024px width.
...and so on. DO NOT WORK WITH PPI in Photoshop or Illustrator. Calculate pixels!!!
It is actually not necessary to go through these steps. While ideally we provide InDesign with a finely crafted bitmap, as long as the effective PPI of the placed bitmap is equal to or higher than an effective PPI of 72, we can always export the epub with an image resolution setting set to 72 PPI in the Conversion Settings.
Here I imported a PNG bitmap in an iPad document. The original PNG's resolution is 2008px by 1782px. Too high for the iPad Retina in portrait orientation, and that does not matter! The effective PPI is 99, and that is more than 72PPI. So when we export to an epub, we simply ensure that the conversion is set to PNG and 72PPI. This will convert our imported bitmap to and EXACT 1:1 version at the native resolution of the iPad retina (because it is placed aligned to the default margins in portrait mode, the final pixel resolution of the width will be 1536 - 36px - 36px = 1464px. The height is inconsequential in a reflowable Epub (up to an extent: depending it will be displayed scaled down to fit...)
So. Back to your @Hosun image prep workflow.
You prepare the vector illustration / diagram in Illustrator. FORGET PPI. Only worry about pixels.
Your options are:
- To create a document at the required pixel resolution in Illustrator. Or to convert the document to the resolution that you need. Then export the PNG bitmap directly from Illustrator for import in InDesign.
This will work. Personally I avoid this approach, because Illustrator is not very good at converting vector art to crisp bitmaps. Or: - create a document at TWICE the required pixel resolution in Illustrator (or convert the document to twice the required resolution in pixels). Then export the PNG bitmap, open in Photoshop and scale it down (down/resample) with Bicubic Sharper (reduction).
This will create a more crisp looking bitmap. Then export as PNG from Photoshop, and import in InDesign.
No need to fiddle around with Smart Objects. Which will not produce as good a conversion anyway.
(PS unfortunately Photoshop does not feature more appropriate downsampling algorithms such as CatmullRom. I prefer this because it results in crisper looking vector to bitmap conversions. Alas, not possible in Photoshop...)
- While (2) may give the best result, there is a much easier workflow that does not require us to prepare a bitmap at all! We just import the SVG from Illustrator (or the AI file)!
I know: you @Hosun stated that SVG is not allowed. Have no fear, because there is a simple trick.
- Place your vector file directly in InDesign. Scale to the size you want on the page.
- Select the frame with the SVG, and select Object-->Object Export Options.
- Rasterise the content, select PNG as the format, and set the resolution to 72PPI.
- Click Done.
Now export your epub once again with the conversion setting of 72 PPI (actually, the value no longer is applied to this SVG because, you set up an object export override that already tells InDesign to export the SVG as a 72PPI PNG!).
Et Voila! The generated PNG version of your diagram graphic is export at the EXACT required bitmap pixel resolution for the iPad at that screen (document) orientation (landscape or portrait - your choice).
The proof is in the pudding: when I crack open that epub (best done with https://www.docdataflow.com/ecancrusher/ because plain unzipping is not quite the right approach) I discover a converted PNG image of that SVG at a resolution of 1465px (the extra 1px is a rounding error introduced by InDesign) because I set up an iPad document in portrait mode.
Finally, it is important to note that if I had used the Google Pixel 2 as the document template, the width in pixels of my exported images would be 1080px. Or 1920px in landscape orientation.
Similarly, the iPhone 8/7/6 template would have resulted in a lower 750px portrait width resolution. The generic Android platform in landscape mode would yield 1280px max width.
And so on.
It is important to decide which digital platform will be your highest end publication target: if the epub is prepared for Kindle Fire/Nook, the portrait resolution would be a width @ 600px. If you export this at 72PPI in the epub export conversion settings, the images will be too low resolution when viewed on an iPad retina screen, which can display bitmap images at more than twice that resolution in portrait mode.
A way around this is to increase the export conversion setting to 150PPI. That will ensure that in the above case a max width image imported in a Kindle document template in portrait orientation mode is exported at 2.0833333 the original size --> 600px * 2.08333 = 1250 px (rounded). This is still less than the 1536px max portrait orientation resolution of an iPad Retina, but will display much better.
BUT! For this to work all placed bitmaps would have to be at an effective minimum PPI of at least twice the 72ppi.
And it is still not possible to reach that iPad target resolution. The only option left would be to switch to 300PPI, but that is COMPLETE OVERKILL and may result in an error message stating that your images use too many pixels. Not to mention the impact on book file size and performance (it WILL slow down readers and reading devices!).
So in the end, as it turns out a much simpler and effective strategy it to simply target the highest end digital platform in InDesign from the very start, and just work with the standard 72PPI effective resolution and export to 72PPI as well. And outside of InDesign PPI is completely irrelevant for bitmap images and digital screen work. Always think in the resolution of the target platform's screen resolution when preparing bitmap images within this context.
Still with me? Pat yourself on your shoulder, and have a nice cup of tea. Or coffee, if that floats your boat. 😉
Anyway. I hope this clarifies some of the confusion here and how InDesign treats bitmap images in digital document templates.
(print templates always work with 300PPI, by the way.)
I do agree the ePub reader situation and the state of the ePub file format itself (as well as eBook files/tech in general) isn't something to be proud of and a rather sad state of affairs...
As for my "treatise" I failed to mention that often exporting to a standard reflowable ePub file at 150ppi or 300ppi the result will display fine on ePub readers because the author / designer imported lower resolution images and InDesign will keep the original resolution of those during export.
That said, it is important to be(come) aware of how InDesign works with bitmap images and the ePub export resolution setting, because:
- nowadays photos and images are delivered at ever increasing resolutions. Typical resolution of Unsplash's free stock photos easily go up to 6000px and beyond. Importing these into your reflowable or fixed epub file and exporting at 300ppi is just a recipe for disaster, because that resolution is maintained! Worse, if the graphics frame is larger than required, InDesign will include that white space in the newly generated version, increasing the resolution needlessy.
- as you probably know, frames drawn in InDesign do not export to reflowable ePubs. This can be fixed by rasterizing those frames with the Object Export settings. But if the user leaves those settings at 300PPI or 150PPI: again, a ridiculously high resolution image will be generated.
- Why is this a problem? Well, Apple books only accept a limited pixel resolution: 5.6 million pixels according to their latest specs at
https://help.apple.com/itc/booksassetguide/en.lproj/static.html#itc1bda991ba
Let's assume we work with the iPad Retina template in InDesign. A typical photo with ~6000px width resolution results in a 30+ million image when exported as an epub at 300ppi. Oops. Exporting at 150ppi is perhaps better? Wrong! 9+ million pixels. Only exporting at 72ppi resolves this issue.
Not even mentioning the limits of other ebook publication platforms and issues during conversion to other ebook file formats when dealing with such unoptimized ePub files... - The same happens to any graphics object created with InDesign's tools and then rasterized with the Object Export settings at 300 or 150 ppi.
- And it happens to vector art imported in InDesign (Illustrator files, SVG files, etc.)
- Yes, that includes imported PDF files. Again rasterized during ePub export time.
Consequences? Suppose the user exports at 300ppi their ePub that contains a few imported vector illustrations, a couple of imported PDF files and decided to use nice high resolution UnSplash imagery (with the average image ~5000px rez). And perhaps a couple of drawn custom objects using the InDesign tools.
Let's test this, because we need real data to prove whether it matters if we export at 72, 150, or 300 ppi. I created a 5 page iPad Retina reflowable document that contains the following imagery:
- a small graphic blown up to fill 2/3 of the first page with two drawn graphic frames with a receded FX look. These frames are rasterized with the Object Export options dialog.
- second page: a coloured frame to fill half the page rasterized with the Object Export options, and two copies of the small low res image that is also used on the first page.
- third page: a full width Unsplash sourced photo of a dog in a field of Lavender with a resolution of 6048 by 4024 pixels.
- fourth page: an SVG diagram taking up the full width, filling the page height ~ 75%.
- fifth page: an Illustrator file containing a nice vector illustration. The same file is placed full width to cover a quarter of the page, and placed a second time at a quarter of that size beneath the first one. The lower half of the page I placed a PDF page of a presentation slide that includes vector text and a bitmap image.
I export the reflowabel ePub at 300ppi, 150ppi, and 72ppi. I also made sure to change the Object Export settings for those InDesign drawn objects to mirror those resolutions for each version. Secondly, I set the image file format to PNG and JPG for each version to compare how much the file size would be affected. The first page is set to rasterize as well in the General ePub settings.
The results!
The 72ppi exported version image resolution fits the iPad target to a T. No issues with images breaking through Apple's "speed limit". And all bitmap images (but for the lores image) will be hitting that iPad Retina screen resolution 1:1. And for other platforms these images will more than suffice as well.
The 150ppi version is problematic: 4 images would trigger Apple's error messaging.
The 300ppi version's images almost all break the 5.6 million pixels threshold.
File size grow (as expected) exponentially: the 5 page PNG at 300ppi epub takes the crown at a whopping ~23MB. With a book that contains a hundred pages and many images it would be problematic to publish such a large sized ebook. Users would probably not be amused to download hundreds of megabytes for just a single ebook. If your book exceeds 650MB it will not convert to Kindle, for example (as far as I am aware - I never hit that limit obviously! 😉 )
Not mentioning the download times and reader / device performance: what would your readership prefer? A fast to download, quick to open and smooth reading experience? Or a slow download, long wait time to open your book on their device/reader, and potentially laggy experience on lower hardware?
And not even mentioning having to deal with the potential issues when attempting to upload such an unoptimized ebook to the main publication platforms and dealing with their technical requirements/limitations?
I certainly know what I'd prefer. 😉
There are also other issues: when you try to work with and test a heavy ePub file in InDesign, export times grow exponentially as well at higher resolutions. Compression of JPG runs faster than PNG, but this simple 5 pager took ~5 seconds to convert to a 300ppi JPG ePub. A PNG version takes longer. And I have a machine that falls in the top 2% as far as hardware goes. It is fast.
It all adds up to a frustrating experience when testing your epub many times.
And finally: for the best quality and file size results each image ought to be compressed with the most appropriate compression method! A vector diagram such as the one shown here by the OP compresses much better as PNG and prevents a degradation in quality at the same time. Win-win: better quality AND smaller file sizes. So by controlling the object export options for each image individually I would end up with an even smaller version that features better quality images!
Lastly, what about sustainability? Your 300ppi or 150ppi ePub would needlessly waste more energy and resources. It's literally a waste of time, resources, energy and hits the environment much harder.
@James Gifford—NitroPressYou said it doesn't really matter and exporting to 150ppi or 300ppi is just fine. I argue against that in this post. It is definitely not acceptable in my ebook (pun intended 😛 ).
And this isn't rocket science. It's not hard to understand, nor will it take extra time to do it properly, because NOT doing it properly and merely relying on the 150 or 300 ppi "make it so" button results in much longer ePub testing times. A little extra time spent at the beginning results in big savings later on when testing and releasing your ebooks on the market and exposing your audience to it.
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