Help with a tiff problem

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Help with a tiff problem

Postby malch on Thu Dec 10, 2009 12:18 am

I am running FPV Build 121 and Windows XP Pro with SP3 et al.

I have been having problems rendering tiff files but only if they have one or more alpha channels embedded within them. FPV is not the only application that has this problem (although some other apps work just fine). I'm guessing that FPV and some of those others are using a Windows library to decode tiffs. Has anyone else seen this problem or have any suggestions concerning how to identify, update. or otherwise fix the appropriate component?
malch
 
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Re: Help with a tiff problem

Postby Axel on Thu Dec 10, 2009 1:05 am

I've a few sample TIFFs with alpha channel from this page and they display fine on XP SP3 and Windows 7. Can you post a link to one such "problem image"?
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Re: Help with a tiff problem

Postby malch on Thu Dec 10, 2009 1:39 am

Thanks Axel. My "problem" images are rather large (90MB) but I took one and simply resized it in CS4 (now closer to 5MB). The resized image still renders in a very mangled state. If I then take it back into CS4, delete the alpha channels and save, it renders fine. Here's the test image; I'll be curious to learn what you observe:

http://www.malch.com/nikon/DSE_4551s.tif
malch
 
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Re: Help with a tiff problem

Postby Axel on Thu Dec 10, 2009 4:15 am

Yes I could see it and it looks like a bug. The image has two 16-bit alpha channels and is read as 64bpp with alpha. When converting to 32bpp with pre-multiplied alpha the pixels comes out with this weird transparency. Applications who ignore alpha transparency seems immune, but I can see this in FPV and also in Live Photo Gallery, Windows Photo Viewer and Media Center (all on Win7) so it's reproducible and this is the good news. The bad news is I cannot do anything about it, except report it and wait for an answer. I'll post here if/when I get some news.
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Re: Help with a tiff problem

Postby malch on Thu Dec 10, 2009 4:31 am

Thanks for looking into this and for your detailed response.
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Re: Help with a tiff problem

Postby Axel on Thu Dec 10, 2009 2:54 pm

Could you email me a screenshot of how the image is supposed to look? I don't see the effect of the alpha channels when opening the file in CS4 (I can get the same look in FPV by ignoring the alpha). Are the electric posts and lines supposed to be visible, or is it just a plain landscape?
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Re: Help with a tiff problem

Postby malch on Thu Dec 10, 2009 6:53 pm

Axel,

Here's the problem tiff again:
http://www.malch.com/nikon/DSE_4551s.tif

And here's a simple JPEG of the same image:
http://www.malch.com/nikon/DSE_4551s.jpg

The power pylons and lines were cloned out and should *not* be visible in the rendered image. They were present when the alpha channels were created by a CS4 script for capture sharpening so they are visible in the alpha channels. But they should not be rendered in the regular image.
malch
 
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Re: Help with a tiff problem

Postby Axel on Wed Dec 16, 2009 4:15 pm

The issue was submitted and the answer is that there is apparently an issue with the handling of multiple alpha channels in the TIFF codec. No word as to if and when the problem will be corrected but awarness has been raised on the issue, which is a good first step :|
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