How to replace PNG images by SVG in epub?

[j.p.s]

Originally Posted by Tex2002ans

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

Thanks!

Originally Posted by Tex2002ans

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

Yes, there was some eye glazing, but also fatigue from trying everything I could think of plus various suggestions over a long time with no improvement. As I wrote before, there are too many variables for me to develop an understanding of what is going on.

With your changes, it works on more devices, and works better on some.

The diagrams still do not display on a Pocketbook 360, which might be partly explained by the the age of the device. (I just now checked, and the ADE reader on the pb360 does display the diagrams. This is the first time I've found the ADE reader preferable to FBreader on the pb360.)

I was about to write that they do not display on the Onyx Boox M92. That is true for FBreader and Coolreader, but Pdf Reader works fine.

In another surprise, the iriver story HD also displays the SVG figures.

The built in reader on the Nook HD+ continues to work, FBreader and Coolreader continue to NOT work.

The Kobo Aura HD and Aura H20 display the SVG with or without the css changes, but there is a problem with Fig 3-21 with the css changes. The width = 100% causes the bottom of the figure to get clipped. This also happens with some of the other readers. On the Aura HD without the changes, some of the figures are a bit small, but are mostly fine. On the Aura H20 without the changes, many of the figures are severely clipped in width and/or height, IMO a step backward from the Aura HD.

I used ebook-convert from calibre 2.75.1 without options to make an AZW3. On a Kindle Voyage, the figures display well in both portrait and landscape. In both modes, the Voyage sensibly limits the figure width if 100% width would cause clipping in the height dimension. Trying to zoom the figures gives bizarre results, but I found all the figures readable without zooming. (Trying to read the smallest for a prolonged period would be painful, though.)

Something I think worth noting regarding comparing different versions of a book on an ereader is that many devices show books by the title from content.opf and it can be difficult to tell which version is which, so I've been teaking the title when I make changes. Just something to consider. (I haven't been changing the UID. No idea what the ramifications of that are.)

[JSWolf]

As I've said many times before, FBReader is a very poor ePub Reader.

[JSWolf]

But, if you are selling this on Amazon, you may need to have fallback images for Mobi unless Kindlegen handles converting the images and the image display code for you.

[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.

(I am going to assume Figure 3-1 is typical of what you are describing.)

I think a few things are going on regarding the small text.

1. The smallest text is very small and light gray. It looks pretty bad in the PNGs. The PDF is even worse, with JPEG artifacts thrown in. I'm mildly curious if the commercial paper version used those or they received extra tweaking and how the figures look in the paper book. I kind of suspect that the smallest text isn't expected to actually be read.

2. The PW2 resolution might not quite be enough to display the text legibly without zooming the image enough to clip it.

3. You didn't say whether the images were full width or tried landscape, or whether the images were larger in landscape than portrait (for images wider than high).

I used ebook-convert from calibre to make an azw3 (FF8) version of Tex2002ans version of the epub. On my Kindle Voyage running version 5.6.1 the figures look great, with some caveats.

The good. The figures are full width minus margins at left and right. For figures too tall to support full width with preserved aspect ratio, the figures are full height minus margins at top and bottom and the width is reduced to preserve aspect ratio. Landscape works and again the figure is enlarged to best fill the frame with correct aspect ratio and imposed margin. In both portrait and landscape a long press on the image followed by tapping the + results in the image zooming enough that the smallest margins are only a few pixels just as for JPEG images in books bought from Amazon. When I did the same with a pre-Tex2002ans version, many of the images were small and attempted zooms gave bizarre results.

The caveats. The smallest text is still tiny in landscape and zoomed. Looking great is subjective. My glasses have polycarbonate lenses with progressive focus and happen to introduce glare. Polycarbone lenses don't attenuate light as much as sun glasses, but they do attenuate enough that in office lighting and darker I frequently can read better with my glasses off even for distances where the glasses give better focus. All this is to explain that I can't read the smallest text with my glasses on, but with my glasses off the smallest text is clear even in unzoomed portrait from about 12 inches.

I think Figure 3-1 on a PW2 in landscape would be comparable to on a Voyage in portrait mode, but physically larger.

[JSWolf]

Originally Posted by j.p.s

2. The PW2 resolution might not quite be enough to display the text legibly without zooming the image enough to clip it.

eInk works differently than LCD. You can take a small image (with text) on a hi-res LCD display and still be able to read the text.

With eInk, if the image is too low a resolution compared to the resolution of the screen, then you won't be able to read it all that well. It's not that the PW2's resolution is too low. It's that the resolution of the image is too low. And it will only get worse on a PW3 or Voyage with a higher resolution screen. Unless you specify to render the image with %, you will have two different sizes on screen of a PW2 vs PW3. And given the poor quality of the image, it will just look worse on a PW3 than a PW2.

[j.p.s]

Originally Posted by JSWolf

eInk works differently than LCD. You can take a small image (with text) on a hi-res LCD display and still be able to read the text.

With eInk, if the image is too low a resolution compared to the resolution of the screen, then you won't be able to read it all that well. It's not that the PW2's resolution is too low. It's that the resolution of the image is too low. And it will only get worse on a PW3 or Voyage with a higher resolution screen. Unless you specify to render the image with %, you will have two different sizes on screen of a PW2 vs PW3. And given the poor quality of the image, it will just look worse on a PW3 than a PW2.

The smallest text in Figure 3-1, as a fully representative example, is slightly more legible to me on my 6" e-ink Kindle Voyage than on my 7" LCD Nook HD. It will be several days before I will be able to get to and check my 6" 768x1024 e-ink iriver story HD, which I believe is the same resolution as the Kindle PW2.

[JSWolf]

Originally Posted by j.p.s

The smallest text in Figure 3-1, as a fully representative example, is slightly more legible to me on my 6" e-ink Kindle Voyage than on my 7" LCD Nook HD. It will be several days before I will be able to get to and check my 6" 768x1024 e-ink iriver story HD, which I believe is the same resolution as the Kindle PW2.

Yes, the PW2 is 1024x758 which is the same as the Story HD.

[AnotherCat]

I think that JSWolf's comments regarding E Ink working differently than LCD are absolutely correct (all else being equal). Further to what he said is that an important part of grayscale display quality is the contrast handling ability of the display. I have not followed E Ink for a year or so on that but as of not very long ago E Ink was capable of only little more than paper, whereas LCD is orders of magnitude better.

Because of this one can expect E Ink to be poorer in displaying greyscale images than LCD, other things being equal. I read a lot of material having grey scale images (and color too) and so no longer use an E Ink reader.

Your Figure 3.1 is a color image (if I am looking at the correct item, I have not followed the whole thread) and if comparing readability of the small grey font as between the Voyage and the Nook then much more than just resolution also comes into play as to readability. For example, contrast through the choice of colors (which is in the hands of the author) and the accuracy of rendition of those by the display and the display's background may mean that on an LCD display with high resolution an image may appear poorer in readability than on a lesser resolution, lower contrast display in greyscale.

In case not known, on color display Android devices one can force them into "Monochrome" by accessing Developer Options (if not open already then Settings>About>then Tap "Build Number" until the options open and are placed in the Settings menu). It varies between versions and devices but under something like "Simulate Colour Space" one can select "Monochromacy". I think the Nook is Android 4 in which case, although I recall the option is still there, it may have a different name.

Viewing the image in "monochromacy" (I don't know how many shades of grey it will be but on recent devices it results in quite good greyscale) on the Nook, if possible, may give a better comparison with respect to the comparable resolution of the 2 devices.

In the end it is wrong to compare the "resolution" of a color image on one device with the same image rendered into greyscale on another, all else being equal, as it is the "readability" that one is comparing. My pick is that one can always produce a far more readable image on an color LCD device compared to an E Ink one, all else being equal, and if one wants to maximize the readability on both then one should maybe start with the color one and select colors and contrast (including the background) that when rendered into greyscale maximizes greyscale readability.

[JSWolf]

Low-res poor quality images will render poorly on a hi-res eInk display. So your screen caps may not display well on a PW3 or H2O or KA1.