Aura H2O Chapter images do not display properply

[heiders]

Hi all,

I have been reading quite a while now on my Kobo Aura H2O (patched latest firmware) and have seen several ebooks with chapter images and somehow they all look faded or greyed out. Only when I switch to the page with the new chapter I see the image in the normal black/dark state for a second or so. But then after the page has fully loaded, it somehow fades to an almost invisible state. I have uploaded a picture which displays this effect. In the indicated red square a chapter image is loaded, but is almost not visible. I am not completely sure if I had this effect on earlier firmware versions as well.

But does anyone know if this is a known bug? And if there is a solution for it?

[frostschutz]

Without having a copy of the book itself (if you modified it in any way using Calibre, a copy of *your* version of the book specifically) so we could perhaps try to reproduce this issue... it's hard to say anything.

Some books just come with low contrast images which might look fine on a regular monitor but can not be given justice on eInk display only 16 levels of grey...

[heiders]

Originally Posted by frostschutz

Without having a copy of the book itself (if you modified it in any way using Calibre, a copy of *your* version of the book specifically) so we could perhaps try to reproduce this issue... it's hard to say anything.

Some books just come with low contrast images which might look fine on a regular monitor but can not be given justice on eInk display only 16 levels of grey...

Although I'm not an expert on these matters, I still doubt that it is a book-related problem, since I see it in all books that use chapter images.
Also, the image is displayed properly for a second or so while refreshing the page, but then when it is done, it kind of looks like the contrast is switched (so black becomes white, white becomes black).

Nonetheless, it might be important to mention that calibre automatically converts all epubs to kepub when adding books to the reader. In addition I have the nightmode patch installed as well (which also switches the contrast), so now I'm thinking of it, this could be part of the problem.

At the moment I do not have access to the file itself, I might be tonight.

[davidfor]

Originally Posted by heiders

Although I'm not an expert on these matters, I still doubt that it is a book-related problem, since I see it in all books that use chapter images.
Also, the image is displayed properly for a second or so while refreshing the page, but then when it is done, it kind of looks like the contrast is switched (so black becomes white, white becomes black).

I've just read a book with a two images at the start of each chapter. One was a globe and the other the chapter number rendered as an image. Comparing what I see on the Glo HD screen with what I see when I open the book using the calibre viewer, I don't think the Glo HD has it wrong. It might be a bit paler than I would expect, but not much. I do see the flash of the darker image during the rendering, but that would be worse for this image

Nonetheless, it might be important to mention that calibre automatically converts all epubs to kepub when adding books to the reader. In addition I have the nightmode patch installed as well (which also switches the contrast), so now I'm thinking of it, this could be part of the problem.

Yes, mentioning that you installed and use the KoboTouchExtended driver is important. The rendering of books is different using the kepub and epub engines, and it might affect this. I have the kepub version of the book I tested from Kobo. It looks OK to, but the image is rendered about half the size of the epub, so it is hard to compare.

[heiders]

Originally Posted by davidfor

Yes, mentioning that you installed and use the KoboTouchExtended driver is important. The rendering of books is different using the kepub and epub engines, and it might affect this. I have the kepub version of the book I tested from Kobo. It looks OK to, but the image is rendered about half the size of the epub, so it is hard to compare.

Thanks for your response, I will try it tonight without using the KoboTouchExtended driver, to see if it changes anything.

[GeoffR]

Originally Posted by heiders

Only when I switch to the page with the new chapter I see the image in the normal black/dark state for a second or so. But then after the page has fully loaded, it somehow fades to an almost invisible state. I have uploaded a picture which displays this effect.

I think this effect is due to the image in the book being made up of light colours, and the renderer displaying it in a progressive fashion; first it is rendered as black/white, then the colours are added.

The basic problem is that the image is too light, perhaps because the publisher has used a greyscale scan of an image that was originally printed in black/white. I think the only solution is to edit the book and use an image editor to darken up the image (or for many scanned images, converting the image to black/white gives the best result.)

In this thread I posted screenshots of a greyscale image converted to black/white.

[frostschutz]

Just looked at the Kindle preview of your book, it seems the image uses very light shade of grey. The biggest part of it is like #eee which is just one shade away from white #fff. The darkest part of the image is #999 but that's like just one pixel in the center of the image, everything else is considerably lighter. So it's a case of next to no contrast, thus turning it nigh invisible on an eInk screen.

For better results you should increase contrast considerably. The following is original vs. Gimp Colors -> Levels -> Auto. Note this feature only works if the original image is not using the full color spectrum... adding a single fully black pixel to the original would not change the image any. In that case you have to play with the contrast controls... or go to the extreme with Threshold but that only gives good results for images that are supposed to be lineart.

The original image should be nigh invisible on eInk, the modified one should be normal.

[DNSB]

Originally Posted by heiders

Hi all,

I have been reading quite a while now on my Kobo Aura H2O (patched latest firmware) and have seen several ebooks with chapter images and somehow they all look faded or greyed out. Only when I switch to the page with the new chapter I see the image in the normal black/dark state for a second or so. But then after the page has fully loaded, it somehow fades to an almost invisible state. I have uploaded a picture which displays this effect. In the indicated red square a chapter image is loaded, but is almost not visible. I am not completely sure if I had this effect on earlier firmware versions as well.

But does anyone know if this is a known bug? And if there is a solution for it?

I've seen quite a few chapter images that are light and others that are dark. It seems to depend on the contrast of the original image and how well they convert to a 16 level display. Remember that the H2O's display is limited to 16 levels of grey (actually, 14 plus white and black) which is not great for displaying an image that was created using 256 or more levels.

If you have access to edit the book, you can extract the images and modify them in your favourite image editor -- I like using GIMP with the 16 grey level palette ( GraysSixteen.zip ) to convert the images so I get a better idea of what they will look like on my ereader's screen and then played with contrast etc. Other occasions, I've simply posterized the image to increase the contrast.