Aura H2O ePub Images Small

[elstoc]

I read quite a lot of scientific / computer ePubs on my Aura H2O, many of which use inline images for scientific symbols and forumlae. However, I've noticed that these images almost always look quite small when viewed on my H2O.

I know I can edit the ePubs directly, and am happy to do so, but I need some guidance on the easiest way to do this, without manually tweaking the dimensions of every single picture - many of my books have hundreds of them.

The one I'm looking at right now has the height and width set to "auto" and I want it just a bit bigger, perhaps 1.5x as big as it is now. Is there an easy way to do this?

[frostschutz]

Maybe you could use KEPUB, I think it lets you zoom images?

Otherwise just set either width or height to 100% (or whatever you feel is appropriate).

Careful when converting books with calibre, it may scale down images depending which output device it's set to. I noticed this too late myself and switched to "tablet" ever since...

[elstoc]

Thanks I'm trying to avoid Kepub at the moment. I did try setting to 100% in the Calibre editor but it made my images look crazy-large. Didn't transfer to my Kobo to test though.

My output is set to 'tablet'.

[elstoc]

For my current read I managed to use find/replace to ensure that the inline stuff had a different class than the standalone images. Then used "height: 1em" for the inline characters/formulae and "width: 90%" for the standalone images (leaving the other dimension as auto).

There were still quite a lot of images that didn't quite work though, entailing some manual resizing (still using width%).

Was a lot of effort and I'd still much prefer to just scale everything identically if I could.

[Ken Maltby]

Originally Posted by elstoc

For my current read I managed to use find/replace to ensure that the inline stuff had a different class than the standalone images. Then used "height: 1em" for the inline characters/formulae and "width: 90%" for the standalone images (leaving the other dimension as auto).

There were still quite a lot of images that didn't quite work though, entailing some manual resizing (still using width%).

Was a lot of effort and I'd still much prefer to just scale everything identically if I could.

I use the "Kindle Voyage" Output profile, for my Aura HD, with calibre.

Luck;
Ken

[elstoc]

Originally Posted by Ken Maltby

I use the "Kindle Voyage" Output profile, for my Aura HD, with calibre.

Luck;
Ken

Thanks, gave that a go too but still no joy. Part of my problem stems from the fact that the images are too small to start with (in the original epub) and I need to scale them up

[elstoc]

Also noticing now that some of the smaller images seem chopped off at the edges in the H2O - an issue not dependent on the input profile. Looks fine in Calibre's viewer/editor.

[davidfor]

Originally Posted by elstoc

Thanks, gave that a go too but still no joy. Part of my problem stems from the fact that the images are too small to start with (in the original epub) and I need to scale them up

Stick with the tablet profile. The main purpose of the profiles is to set the maximum size of the images. If you do a conversion, all images larger than this will be shrunk. Smaller images will not be touched. Not shrinking the images gives the best long-term results and flexibility.

Originally Posted by elstoc

Also noticing now that some of the smaller images seem chopped off at the edges in the H2O - an issue not dependent on the input profile. Looks fine in Calibre's viewer/editor.

For most images, I use the following code:

<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" version="1.1" width="100%" height="100%" viewBox="0 0 963 1400" preserveAspectRatio="xMidYMid meet">
        <image height="1400" width="963" xlink:href="../images/cover.jpg"/>
      </svg>

The numbers have to be adjusted to match the size of the image. And it is usually wrapped in a div to centre it.

With this, if the image is to large for the screen, it is resized to fit. If it is to smaller than the screen, it will simply be centred. There are probably ways to change this to have smaller images fill the screen, but I have played with that.

[elstoc]

Thanks everyone. I've decided to stick with the tablet profile so that my images don't get shrunk any more.

I think some more experimentation is in order. Unfortunately most of the images in my books are a mix of single character, single equations, tables and full-screen screenshots so unless I can just scale the images up from their current dimensions, I suspect manual tweaking is going to be the only way to go. I'm slowly discovering that image handling on ePubs is a bit of a nightmare.

[GeoffR]

How has the publisher specified the image size in the stylesheet?

If they have used an img style with a height and width of auto or height and width not specified at all then the image will display at its natural pixel size with no scaing. In that case you could easily scale up all the images by exploding the book in Calibre and running an image manipulation tool in the book's images directory. For example in Linux with the image magic tools you could make all JPG images 50% bigger by running:

for F in *.jpg; do convert -resize 150% $F $F; done

But really, all images in an ePub should be displayed at a size proportional to the font size (em), or screen size (%), or in some rare cases absolute size (mm, pt, etc.) Any publisher that displays the images in pixel (px) sizes is just ensuring that the images will be the wrong size on every device with a pixel density different to the one they tested on. The only way to fix that sort of mistake properly is to go through the book and correct each individual mistake. by hand.

[JSWolf]

The problem is that a lot of eBooks use low resolution images and on a device with a high resolution screen, the images will be small. Yes you can increase the image size, but some low resolution images will come out fuzzy as you are increasing the size of poor quality low resolution images.

Publishers need to learn that because we now have high resolution devices, we need high resolution images. But there is a downside to that. Because of low resolution devices, those high resolution image may not fit on screen properly or take up too much room on screen.

[elstoc]

Thanks GeoffR and JSWolf. The images are specified with a height and width of 'auto' and are therefore displaying without scaling. When I scale up the images using either height (=1em) or width (=80%) they are pixellated but at least I don't have to hold my ereader up to my face to see them.

I do like the ImageMagick idea (I already use this before uploading photos to my website). I think that might be my next experiment.

[GeoffR]

I just discovered that mogrify is the batch version of the convert command, so

mogrify -resize 150% *.jpg

is a simpler way to do what I posted before.

[elstoc]

I think that's got it. Thanks again GeoffR.