Any way to get background color info using JavaScript?

Posted on 2004-10-29
Last Modified: 2008-03-17
I know you can get a GIF's height and width, but I'm
wondering if there's anyway to retrieve its background
color. From what I understand, it's stored in the GIF
header right along with the height & width information,
so I'm curious if it's possible.

Failing that, is there anyway to dynamically rename a
GIF to a different file. In other words, can you change
the name of "image.gif" to "image.txt" somehow? If
so, you could just pull in the text file and read the
background color info. But I can't figure out how to do
that either!

Any suggestions are welcome
Question by:sleepybear

    Author Comment

    Oops. I suppose I should have mentioned that I meant to
    add... "any way to do this in JavaScript?"

    Hopefully, since this IS in the JavasScript section you guys
    figured that out.
    LVL 31

    Accepted Solution

    not client side. The only things exposed off the header of an image file to JS are the heigth and width. see

    You can not change the extension using JS programatically
    LVL 31

    Expert Comment

         You have access to 4 bytes of info in the header (ie height and width) this is 32 bits. By limiting your chars to alpha-numeric and a just a few special chars with  compression you can get it down to between 4 and 5 bits per char (if you are really smart with the compression depending on the message type you could even get this down lower). Bascially you are looking at about 6 or 7 chars per header, this is not a lot and you would require about  40 images for 256 chars.

    LVL 31

    Expert Comment

    the width and height in the header can be edited with a hex editor on say with a 3 by 3 .bmp to be 63000 by 45987 and the file will still be tiny, the file can be loaded and not displayed with the data extracted, I tried it.  But still not much data per image.

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