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MECC Bitmap Compression

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jawharp
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MECC Bitmap Compression

Post by jawharp » Sun Sep 11, 2016 4:18 pm

Hey guys,

I've been trying to figure out how some bitmap files I extracted from an archive for the game "Opening Night" for quite some years now, and I'm closer than ever but still stumped. I was wondering if anyone here has ever heard of image compression like this.

The files are in a folder called "CBMP," so I'm 99.999% sure they're bitmaps. They have been heavily compressed. Some of the larger files contain multiple images within them (I think it's for animations in the program).

They have a custom 14 Byte header that has the following little endian values:

# of images in the CBMP file (short)
XSize (short)
YSize (short)
Offset of the Bitmap Data (long)
Size of the Bitmap Data (long)

After that is the bitmap data itself. A while back, someone said they looked like RLE bitmaps, but I think there's something else going on. From what I've researched, bitmaps draw their images in scanlines from the bottom up, or from the top down. When I modified some of the bitmap data just to see what it would do in the program, it appeared that the image was being drawn in 8 pixel chunks from the top left down. It would go down one column, then start the next column from the top again. Here's a picture to show you what I mean.

There are also separate files for the color palette. The palette is not encoded in any way, just the bitmap data.

I've included a link to some of the CBMP files and the color palette file here: http://s000.tinyupload.com/index.php?fi ... 1282341502

If anyone has a minute, I'd appreciate any info you'd have on compression like this. It seems like a weird custom thing, and I'm not sure how to go about reverse engineering it.

Thanks,

:twisted: jawharp :twisted:
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huckleberrypie
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Re: MECC Bitmap Compression

Post by huckleberrypie » Mon Apr 24, 2017 7:45 am

Bumping this so more people can look into reversing the game (and American Girls Premiere for that matter, no thanks to Lazy Game Reviews doing an episode on this).

Apollo
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Re: MECC Bitmap Compression

Post by Apollo » Tue May 16, 2017 12:59 pm

https://msdn.microsoft.com/en-us/library/dd240593.aspx

I looked shortly at it and came upon that, just a guess but could be interleaved RLE bitmap encoding perhaps, need some programmer try it all out.

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