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Old 12-28-2006, 06:00 AM   #1
ghostwheel
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optimal resolution for images?

Hi,

I've been working on a djvu2lrf script, and while trying to optimize the output encountered the following problem:

It seems that no matter what the resolution of an image is, the sony reader will always try to do some scaling!

To test that, I created an lrf file using makelrf with images of various sizes, all of which contain very simple patterns. If the pattern displays uniformly on the screen, no scaling is happening, and if stripes occur, some scaling is happening.
The result was that even an image of size 306x306 is scaled

Since I have not yet installed the CONNECT software, I'm not really sure that I created the files correctly.

I attached the BBeB (.lrf) file, and the original images.

I have a couple of questions:
1. does the BBeB file display correctly in Windows?
2. Do you also see the problem on your readers?
3. Does anyone know why the reader scales any image and whether this can be prevented?

Thanks!
Michael
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Old 12-29-2006, 05:38 PM   #2
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Ok, just an update. I seems that the files look just as bad in the connect software on my PC. However, when I decompose the lrf file to its components, I get the gifs intact. I think the problem might be in the makelrf program. It creates a 600x800 page from images, and embeds them with margins of the right size for that page. However, the reader has pages of size 600x766 (I think), and thus they are shrunk. When you look at the GIFs themselves, not embedded in an LRF file, they look fine.

Any ideas how to fix makelrf?
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Old 01-01-2007, 05:28 AM   #3
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Problem solved (?)

I finally did manage to solve the resolution problem. (The fact that the CONNECT software is identical to the reader display helped a lot, since I didn't have to load the files to the reader every time...)

It seems that the document dimensions are relevant. 580x754 works well, other resolutions (any number other than 754 in the range 750-768, numbers larger than 580) do not seem to work. The numbers in the "page box" size do not seem to matter - they can be larger than the document dimensions.

If anyone can shed a light on what is going on, it would be great. Once these dimensions are used, pages display very nicely, and are quite readable. If this problem also exists in PDFrasterFarian, then using 580x754 could make pages even more readable!

I attached a working lrf file or the gifs mentioned im my first post.
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Old 01-01-2007, 08:48 AM   #4
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Are you saying, then, that approx 580x754 is best for the Sony Reader in general, or just best for makelrf? (It sounds like you guessed that the "real" resolution is approx 600x766).
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Old 01-01-2007, 12:17 PM   #5
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I haven't understood the problem exactly. I was playing with the source of makelrf, and there it seems that a "page size" of 580x754 works best. However, irrespective of the page size, images contained in the lrf file can be bigger and will be fully displayed, up to some size. I think that the reader can display images up to a size of 600x766 (I'll test that exactly).
It could be that it still is a problem of makelrf, and some other parameter of the lrf file isn't set correctly. It would be intetesting to try to make an lrf file out of the GIFs I supplied above using lrs2lrf and see if the same problem occurs. As far as I could see, since BBeBook is a direct port of makelrf to java, it should have the same problem.
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Old 01-01-2007, 01:59 PM   #6
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max res on screen seems 583x753

If you look at the attached lrf files, you will be able to see that the effective resolution (for this file at least) is 583x753 (you can count pixels...). This shows up both in the CONNECT software and on the reader. The document resolution is set to 584x754. When I try 585x784, size reduction starts to kick in.

So, now I'm fairly certain that the max resolution of an image in an lrf file that can be exactly displayed is 583x753.

I just noticed the PDFrasterfrasian 2.0 uses 565x754 as the resolution of images, with document size 600x800, and pages of size 600x768...
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Last edited by ghostwheel; 01-02-2007 at 09:40 AM.
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