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Obscure graphics format help?
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Joined: 09 Feb 2015

PostPosted: Wed Mar 09, 2016 5:24 pm    Post subject:  Obscure graphics format help?
Subject description: calling people familiar with or have fancy tools to decipher afile format
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So a friend of mine sent me some extracted drawings for a Datsun 240Z he's restoring... the images were extracted from some old software and have generally the quality of a fax. The diagrams are all unaliased and unblended, black and white line drawings, assumption here is that it's related to fax, but if nothing else, still 1bpp.

Having looked at the files, they are structured in blocks of 2100 bytes, the block header is 30 (contains at the least a block id at byte 12), the tail is 22 @'s and discardable. Thus each file is a multiple of 2100 bytes, and leaves exactly 2048 bytes for image data per block. Most files come very close to the block boundary at the end, but some end up padded with zeros in the last block.

The header doesn't change throughout the same file, aside from the block id, which starts at F1 and counts up, but I haven't seen files larger than 9x2100, so if FF is the last possible id, that wouldn't be an issue. The headers are not consistent between files of the same filesize/blocksize, which leads me to believe the header might contain other data, like how many rows or columns to pad the top left, and start the image data offset. A quick scan for common integer types using byte boundaries yielded nothing, so if it stores numbers, it's probably sub-byte format like 4-7bit.

The images appear to have a similar aspect ratio despite size, so there could be an implicit ratio to determine image dimensions. It is also a slim possibility they encoded like Nintendo did, with small squares of 8x8, 16x16 or other size to create a tiled image. I have no idea of byte order or row order, could very well be drawn bottom up.

It seems logical they modified a fax machine to get their literature scanned into the program, and being in Japan, I'm sure they had all the technology of the day to draw upon. If there is compression, I would expect it's something very basic like LZW or other something like we use in .shp editors, there are lots of diagrams, and it would have been maddeningly slow to decode/process on the shitty computers of the day.

What is known with near certainty, most images have lots of whitespace at the top left, they are not high resolution images by any means, and the colour-depth is 1 bit.

Check below for some of the files...  any help figuring out the format or converter would be appreciated.

 Filesize:  101.99 KB
 Viewed:  1042 Time(s)


 Filesize:  131.75 KB
 Viewed:  1042 Time(s)



 Filename:  s30diagram.zip
 Filesize:  81.23 KB
 Downloaded:  5 Time(s)

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Joined: 14 Sep 2006
Location: Constant Flux

PostPosted: Wed Mar 09, 2016 11:10 pm    Post subject: Reply with quote

That my friend, looks like an ArcDraw file saved as a BMP via a Plotter. Especially since the header is (a 9-byte?) japanese ASCII (which I can't read btw).

http://www.wss.co.uk/pinknoise/Docs/Arc/Draw/DrawFiles.html is the only thing I can find on the ancient thing.
"A Draw file containing a file header but no objects is legal; however, the bounding box is undefined. In particular the 'x0' value may be greater than the 'x1' value (and similarly for the y values)."

Nigh-impossible to find a file made from that software anymore to compare anyway.
"Don't beg for things; Do it yourself or you'll never get anything."
Lin Kuei Ominae wrote:
wrong forum. this is not minecraft.

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