How to replace PNG images by SVG in epub?

[j.p.s]

Originally Posted by jhowell

I do not use EPUB readers, I use Kindles. As an experiment I converted your revised book using kindlegen and loaded it on an e-ink Kindle running the latest firmware version, 5.8.9.2. The SVG images displayed, but the text was a bit small for my eyes. Kindles have the ability to magnify images, but when I tried that with the SVG images they did not display correctly.

Thanks. I'm certainly curious how Kindles handle SVG images, but I guess it would be best to test with known good input. Since the epub now passes epubcheck, maybe this one is.

[JSWolf]

Originally Posted by j.p.s

The source is at: https://github.com/progit/progit

It looks to me like a single file html file is generated and calibre is used to make epub and mobi. pdf is generated separately.

Is the code good to go once it's generated? If so, it would be best to use Sigil or the Calibre editor to split the HTML instead of converting if the code is good to go otherwise.

[j.p.s]

Originally Posted by JSWolf

Is the code good to go once it's generated? If so, it would be best to use Sigil or the Calibre editor to split the HTML instead of converting if the code is good to go otherwise.

I don't know. I have no connection with the project, don't know the details of how the HTML gets generated, and never expected to end up this deep down the rabbit hole. It beats me why the HTML was not generated as one file per chapter.

I had expected to just need to substitute the SVG images for the PNG images and change the references from image/png to image/svg. It's obviously more complicated than that, but I'm also begining to suspect buggy epub reader software, but that this book is enough off that it is not good for proof of that.

[Tex2002ans]

Originally Posted by j.p.s

I couldn't find a dia exporter with an option to select an SVG ouput version, and the w3c SVG validator didn't like the DTD in the SVG 1.0 files either. I edited the SVG version to 1.1 and changed the DTD to match the w3c SVG 1.1 DTG and every browser I tried rendered the figures at least as well as when they were labeled SVD 1.0, so I made a tip-toe of faith and checked a dozen or so against the w3c validator. All of them passed.

You could open up those 1.0 SVGs in Inkscape and save them as "Plain SVG". It should convert everything to 1.1 for you.

I tested "progit-svg11-xml-img-auto.epub" on my Nook. Displays ok.

But like jhowell mentioned, probably best to change the SVGs to be more EPUB-standards-compliant.

Originally Posted by j.p.s

Thanks. I'm also curious whether the figures display on your Kobo aura or any of your Sony e-ink devices. If not, is there some change to any part of the epub that will cause any e-ink device to display at least one of the SVG figures?

The only thing you want to do is go into your code:

<p class="calibre3"><img width="100%" src="../Images/18333fig0101-tn.svg" alt="Figure 1-1. Local version control diagram." title="Figure 1-1. Local version control diagram." class="calibre6"/></p>

and remove the "calibre6" class:

.calibre6 {
    height: auto;
    width: auto
    }

that code is interfering with the SVG stretching to the full width of the screen on some viewers.

Ultimately, what I would recommend doing is changing it to this:

Spoiler:

<div class="svgimages"><img src="../Images/18333fig0101-tn.svg" alt="Figure 1-1. Local version control diagram." title="Figure 1-1. Local version control diagram." class="svgimage"/></div>

with this CSS:

Spoiler:

div.svgimages {
	margin-left: 0;
	margin-right: 0;
	text-align: center;
}

img.svgimage {
	width: 100%;
}

this allows you to easily control all the SVGs in a single location.

Originally Posted by j.p.s

Again, while I want the image to display optimally, I mainly want the SVG to display at all, which for most epub readers that I have tried it does not.

Which readers specifically did you try? Most of the Android readers do not follow the EPUB standards... and/or do complete CSS overrides.

Originally Posted by jhowell

I do not use EPUB readers, I use Kindles. As an experiment I converted your revised book using kindlegen and loaded it on an e-ink Kindle running the latest firmware version, 5.8.9.2. The SVG images displayed, but the text was a bit small for my eyes. Kindles have the ability to magnify images, but when I tried that with the SVG images they did not display correctly.

If this is for personal usage (and you only use Kindles that support KF8), then sure you could keep the SVG images in the book.

But if it's for actual sale, you have to take into account older Kindles (MOBI). You would then need JPG/PNG fallbacks (this is explained in section 17.3.2.2 of the "Amazon Kindle Publishing Guidelines").

If you needed to generate PNGs, I would recommend taking those SVGs and generating higher quality PNGs from them, sort of like how I explained in my "Tutorial: Formulas to PNG" topic:

Manually using Inkscape: Post #2
Automatically using Imagemagick: Post #19

All you have to do is just tweak that .bat file in Post #19 slightly by changing "*.pdf" into "*.svg":

Spoiler:

FOR /F %%k IN ('dir /b .\*.svg') DO (
convert -density 350 %%k ^
    -background white -flatten -trim ^
	-depth 8 -colors 17 ^
    %%k.png
)

that'll generate all the SVGs in a given folder into high quality PNGs (350 DPI).

Side Note: You have to be careful with some characters that are included in these SVG files though. For example, in 18333fig0104-tn.svg, the author is using a 𝚫 (U+1D6AB : MATHEMATICAL BOLD CAPITAL DELTA) which probably doesn't exist on many fonts. You'll probably want to substitute in a normal Δ (Greek Capital Delta).

Originally Posted by jhowell

The SVG images displayed, but the text was a bit small for my eyes. Kindles have the ability to magnify images, but when I tried that with the SVG images they did not display correctly.

... yeah... this is one of the downfalls of SVG on the current devices. They just don't support it as well as bitmap images. Not being able to Zoom is one of the disadvantages. And there are still a lot of buggy cases such as changing fonts/backgrounds/colors/Night Mode:

https://www.mobileread.com/forums/sh...44#post2852244

or not scaling properly in some readers:

https://www.mobileread.com/forums/sh...40#post3515940

Not too sure how well Text-to-Speech is handled within SVG images either (haven't tested this thoroughly yet).

Theoretically I am all for vector images over their bitmap counterparts... but practically, the damn readers have a while to go. Good to plan for the future though and store your vector sources, so you could always generate higher quality images at a later date (part of the reason I wrote that tutorial. Some sort of middleground while waiting for higher DPI devices + MathML support to get better).

[willus]

Just a data point: all of the posted epubs display fine in iBooks on a vintage (2010) iPad running iOS 5.x.

[j.p.s]

Originally Posted by willus

Just a data point: all of the posted epubs display fine in iBooks on a vintage (2010) iPad running iOS 5.x.

Thanks, that is interesting.

I was about to write that I would think the PDF version would be best for tablets, but I've just noticed that the PDF version uses raster images for the diagrammatic figures.

[j.p.s]

Originally Posted by Tex2002ans

(Lot's of really good information...)

... that is going to take me a very long time to digest.

[j.p.s]

My takeaway is that many epub readers on e-ink devices do not have good support for SVG images, but that my various attempts to substitute SVG images for PNG images in the Pro Git book are not good tests of SVG support in epub readers.

I tried an epub version of "SVG 1.1 2nd Edition Test Suite" a few years ago, but that was not helpful. By the way, I can't find this book now, only W3 web pages with individual tests.

I may eventually put together an epub written specifically to try all the suggestions here plus everything else I can think of.

I must say that I am very disappointed that HTML with simple references to PNG and JPEG image files works just fine in epub readers, but not for SVG in most epub readers on e-ink devices, including FBreader. Especially since they work fine in desktop FBreader and ipad and even somewhat in epub converted to azw3.

[salamanderjuice]

Originally Posted by j.p.s

My takeaway is that many epub readers on e-ink devices do not have good support for SVG images, but that my various attempts to substitute SVG images for PNG images in the Pro Git book are not good tests of SVG support in epub readers.

I tried an epub version of "SVG 1.1 2nd Edition Test Suite" a few years ago, but that was not helpful. By the way, I can't find this book now, only W3 web pages with individual tests.

I may eventually put together an epub written specifically to try all the suggestions here plus everything else I can think of.

I must say that I am very disappointed that HTML with simple references to PNG and JPEG image files works just fine in epub readers, but not for SVG in most epub readers on e-ink devices, including FBreader. Especially since they work fine in desktop FBreader and ipad and even somewhat in epub converted to azw3.

I just tried the file you attached loaded on my Kobo Aura One via. Calibre and the KoboTouchExtended plugin(so as a kepub) on the latest firmware. It seems to load the diagrams fine. Although they are pretty small on the screen.

It looks like this.

[j.p.s]

Originally Posted by salamanderjuice

I just tried the file you attached loaded on my Kobo Aura One via. Calibre and the KoboTouchExtended plugin(so as a kepub) on the latest firmware. It seems to load the diagrams fine. Although they are pretty small on the screen.

It looks like this.

Thanks!

It is good the hear that the images get rendered. But unless I can get them larger than the PNG images are shown, it doesn't actually help with the original problem. (Well, the file size is smaller, but I think that is secondary when the displayed images are still to small.)

[fbrzvnrnd]

Originally Posted by j.p.s

Thanks!

It is good the hear that the images get rendered. But unless I can get them larger than the PNG images are shown, it doesn't actually help with the original problem. (Well, the file size is smaller, but I think that is secondary when the displayed images are still to small.)

About the size problem, you have to follow the Tex2002ans suggestions. The calibre css are not right.

[Tex2002ans]

Originally Posted by fbrzvnrnd

About the size problem, you have to follow the Tex2002ans suggestions. The calibre css are not right.

I attached the EPUB with the minor CSS tweaks I mentioned in my post.

Seems like someone's eyes glazed over before implementing the solution.

Originally Posted by j.p.s

I must say that I am very disappointed that HTML [...] but not for SVG in most epub readers on e-ink devices, including FBreader. Especially since they work fine in desktop FBreader and ipad and even somewhat in epub converted to azw3.

Works fine in ADE/RMSDK + Readium (which would cover the vast majority of spec-compliant readers). Should work fine on Kobos as well (salamanderjuice or someone else could test the tweaked one).

I wouldn't rely on FBReader for anything. It is a reader that throws the EPUB-standards out. Similarly with Moon+ Reader or many of the billions of other Android readers out there.

They can "read EPUB" (aka, rip the HTML out, overwrite the CSS, and try to treat it like a "normal web page" or document). That might fly if you mostly read fiction or text-based non-fiction... but once you get into the more complicated layouts and functionality, they can't be relied upon. (Complex tables, poetry, SVG, various methods of EPUB3 Footnotes, MathML, pagelists, etc. etc.).

If you are reading on Android, some of the spec-compliant readers are Bluefire, Bookari, Gitden Reader.

Side Note: I don't have any first-hand experience with iBooks (I wouldn't touch an Apple product with a ten-foot pole). If anyone has iBooks on their devices, if they could test this EPUB and report back how the SVGs scale/look, that would be great.

[salamanderjuice]

Originally Posted by Tex2002ans

I attached the EPUB with the minor CSS tweaks I mentioned in my post.

Seems like someone's eyes glazed over before implementing the solution.



Works fine in ADE/RMSDK + Readium (which would cover the vast majority of spec-compliant readers). Should work fine on Kobos as well (salamanderjuice or someone else could test the tweaked one).

I wouldn't rely on FBReader for anything. It is a reader that throws the EPUB-standards out. Similarly with Moon+ Reader or many of the billions of other Android readers out there.

They can "read EPUB" (aka, rip the HTML out, overwrite the CSS, and try to treat it like a "normal web page" or document). That might fly if you mostly read fiction or text-based non-fiction... but once you get into the more complicated layouts and functionality, they can't be relied upon. (Complex tables, poetry, SVG, various methods of EPUB3 Footnotes, MathML, pagelists, etc. etc.).

If you are reading on Android, some of the spec-compliant readers are Bluefire, Bookari, Gitden Reader.

Side Note: I don't have any first-hand experience with iBooks (I wouldn't touch an Apple product with a ten-foot pole). If anyone has iBooks on their devices, if they could test this EPUB and report back how the SVGs scale/look, that would be great.

Yep, works fine on my Kobo Aura One. Images are scaled to fit the width of the margins now right?

[JSWolf]

Originally Posted by salamanderjuice

Yep, works fine on my Kobo Aura One. Images are scaled to fit the width of the margins now right?

Looks like it when I adjust the ADE window width.

[asleyam]

Originally Posted by Tex2002ans

Side Note: I don't have any first-hand experience with iBooks (I wouldn't touch an Apple product with a ten-foot pole). If anyone has iBooks on their devices, if they could test this EPUB and report back how the SVGs scale/look, that would be great.

Here is how they look in iBooks in the 10.5" ipad. Portrait and landscape modes.

https://imgur.com/a/BMp8p