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TOPIC: Resampling

Resampling 10 months 1 week ago #5588

MajorMushroom

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I've been using YACReader for about a month and it works amazingly for my needs. One small issue I have had is with page resampling. I realise that pages will have to be resampled to view on a differently sized screen, and I know that this is a process which can result in some loss - however in my experience resized pages have been very blurry, much more than I would have expected.

Here's one example, from a manga where the page size was almost exactly identical to my monitor size making for a good comparison. Switching between the two images in two tabs, the blur is fairly significant.





I know that some of this is inevitable, but is there any way I can get slightly sharper pages when resampling? I've had to resort to viewing at original size, even for pages that are *just* bigger than my screen, because the considerable blur introduced by even very small resizing is very obvious and also makes small text quite hard to read. Thanks!
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Resampling 10 months 1 week ago #5591

Luis Ángel

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hmmm, what's the resolution of your screen?
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Resampling 10 months 1 week ago #5594

selmf

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Yes, I'm aware of the problem. YACReader uses the stock resampling algorithms provided by the Qt toolkit and these do not provide the same crispiness ass advanced filters like LANCZOS and some others. I have experimented with some filters in the past, but I never found a satisfying solution to transparently integrate them into YACReader.

So … basically … a slight unsharpness is to be expected. Not much we can do about it unless we add better rescaling algorithms.
My answers are not necessarily official YACReader statements but mostly represent my own opinion in technical matters.
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Resampling 10 months 1 week ago #5595

Luis Ángel

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@selmf, but he is reporting “ resized pages have been very blurry” and that doesn’t match the expected output....

I couldn’t see a difference in the screenshots, maybe you can send the images to me by email?
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Resampling 10 months 1 week ago #5598

MajorMushroom

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Thank you both Selmf and Luis Ángel for your responses. The full size images are here;

i.imgur.com/byWWYZe.png
i.imgur.com/d7bbeId.png

I may have been exaggerating when I said that the images were "very blurry," but the blur is certainly visible and unpleasant. It is nothing more than what selmf described, that without e.g. lanczos there is no way to get sharper output. I was simply wondering whether anything could be done about this from an end-user view, but I gather the answer is "no." I hope that you do consider such an integration in the future, but thanks again regardless for your work on YACReader.
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Resampling 10 months 1 week ago #5599

selmf

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The toolkit simply does not support it at the moment. There are some implementations out there that maybe could be made to work (KWin from KDE has a lanczos implementation, so does Krita).
What I experimented on was doing it via OpenGL shaders, which is an efficient way to do this without introducing extra CPU stress and lag. The main reasons this never resulted in anything concrete were constant problems with OpenGL on Windows systems and the fact that I did not find a way to just plug in these shaders into our code without replacing our viewer widget with custom code.

With the way the Qt toolkit is currently headed, OpenGL support is actually detoriating and I suspect it might become unusable on Windows and it will likely disappear from OS X, so if I'd ever return to this feature I will have to rethink on how to implement it ...
My answers are not necessarily official YACReader statements but mostly represent my own opinion in technical matters.
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