Difference between revisions of "Talk:Riven tBMP resources"

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(that's me)
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[Tito] I think I've seen Aaron's effects in some compressed tBMPs. In particular, I recall being surprised by observing duplets repeating themselves, though I don't remember which tBMPs I was inspecting at the time.
 
[Tito] I think I've seen Aaron's effects in some compressed tBMPs. In particular, I recall being surprised by observing duplets repeating themselves, though I don't remember which tBMPs I was inspecting at the time.
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[ [[User:Aaron|agrif]] 06:55, 23 February 2009 (CET) ] I mean to go back and check specifically for this, but I'm almost completely certain that this is true. Initially, in my algorithm, I used an unsigned integer to represent the number of pixels to look back from where I started, and decremented it each time I copied a pixel. This crippled all my images, and caused weird segfaults when it rolled over after 0. This was fixed when I used a signed integer type (ie let the command copy into newly-written pixels). This is basically an implementation detail, most people would do it a different way where this doesn't matter, or use a signed integer to begin with. [also, I think that pixel-based lookbacks ignore the extra space off the edge, while duplet-based ones do not, but I'm not certain on that. I'll verify that too, but it's too late now.] I didn't realize this was new information, I just thought it was left out.

Revision as of 06:55, 23 February 2009

Aaron, I'm not entirely clear on your recent additions to the tBMP decode algorithms. Are you aware of specific images that exhibit the behaviors you describe to use a test cases, or a decoder implementation which respects those details?

[Tito] I think I've seen Aaron's effects in some compressed tBMPs. In particular, I recall being surprised by observing duplets repeating themselves, though I don't remember which tBMPs I was inspecting at the time.

[ agrif 06:55, 23 February 2009 (CET) ] I mean to go back and check specifically for this, but I'm almost completely certain that this is true. Initially, in my algorithm, I used an unsigned integer to represent the number of pixels to look back from where I started, and decremented it each time I copied a pixel. This crippled all my images, and caused weird segfaults when it rolled over after 0. This was fixed when I used a signed integer type (ie let the command copy into newly-written pixels). This is basically an implementation detail, most people would do it a different way where this doesn't matter, or use a signed integer to begin with. [also, I think that pixel-based lookbacks ignore the extra space off the edge, while duplet-based ones do not, but I'm not certain on that. I'll verify that too, but it's too late now.] I didn't realize this was new information, I just thought it was left out.