in reply to GIF Image Processing

I want to process to detect edges without decompressing the image first.

You want to detect edges before you decompress the image? Are you sure? Most edge detection algorithms depends on having a matrix of pixels. That implies decompression. If you don't want to decompress all at once, you'll at least have to do some sort of banding algorithm to get an uncompressed band of scanlines, with enough scanlines to do incremental edge detection on. I've not heard of anyone having done this, but GIF decompression algorithm certainly makes this possible.

Unless you're under really tight space constraints, you'll get there a lot quicker if you decompress first.

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Re: Re: GIF Image Processing
by gri6507 (Deacon) on Jan 22, 2002 at 05:44 UTC
    To asnwer your question - yes, I want to detect edges without decompression. I realize that this is not going to be very accurate. However, I'm not going for accurasy, I'm going for crude functionality and SPEED.

    I have done research in the past, and I know that detection without decompression is possible for JPEGs (see here) JPEGs are much more involved in encoding. If it's possible to do edge detection with JPEGs, I only assume that it is also possible to do it with GIFs since that encoding algorithm is MUCH simpler.

[reply]
      Jpegs are in my understanding, store rectangular sections of the image ( If I remember stored coefficients), so I guess you could do edge detection as the compressed data represents some sort of semblance to what is encoded, but GIF's are just LWZ encoded chunks. I don't see any way you could determine what's in it without decompressing.

      -Lee

      "To be civilized is to deny one's nature."
[reply]

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