Message-Id: <mailto:199507191643.LAA29612@library.wustl.edu> Date: Wed, 19 Jul 1995 18:34:44 GMT From: Levine Emil <mailto:levine@NEPO1.IAEA.OR.AT> Subject: Re: GIF inline images in WWW pages To: Multiple recipients of list IMAGELIB
This is to introduce myself and my project. Emil Levine, Head, International Nuclear Information System (INIS) Clearinghouse, International Nuclear Information System, Vienna, Austria. We are beginning a pilot and eventual operational system to annually put about 500,000 pages of electronic surrogates or reports from our world wide member states on CD-ROM. (Currently available on microfiche.). Hello to my colleagues and standby for lots of questions. ---------- From: IMAGELIB To: Multiple recipients of list IMA Subject: Re: GIF inline images in WWW pages Date: Tuesday, July 18, 1995 2:12PMOn Mon, 17 Jul 1995 09:07:42 -0400 Pamela Mason said:
Pamela: (I'm behind in reading my mail and you've probably heard more about this than you care to, but... :-)
>I have been doing some reading on browser support of GIF images and there
>seems to be a lot of advice (which I think may be erroneous) that if one
>uses fewer colors in a GIF image for inline display the file will be
>smaller.
This is true. GIF has 8-, 4-, 2- and 1-bit compression schemes. A bi- color (1-bit) file can be very small. Since GIF is lossless and has a very simple compression scheme: output N pixels of color M, it compresses areas of constant color (borders, etc.) very efficiently (much better than JPEG!).
>Other sources seem to indicate that after about 5 or 6 images are
>displayed by a browser, the "colors are used up" and no more images can be
>displayed on the page.
This depends on your video card and Windows/Mac configuration. If you have 15- or 16- bit color capability, you can have lots and lots of 8-bit-color images at one time. If not, the background images will have their colors "trashed" but are properly restored when brought to the foreground.
>My understanding of GIF files is that they are all
>8-bit, 256 color images, meaning that a maximum of 256 colors *can* be
>displayed, not that these are always present. In fact, if one saves a
>bitonal image of text as a GIF file, it is saved as 8-bit color, even
though >what is displayed is only black and white.
It can be saved as an 8-bit image which happens to have only 2 colors. However, as I mentioned, it can be much more highly compressed by using 1-bit GIF compression.
> What affects the file size in
>GIF files, since they are all 8-bit color, is resolution and the image's
>dimensions.
Yes. An image with 256 colors and very fine detail will not compress well in GIF. In the worst example, random colored dots, there would be no compression, in fact, the file would be larger than bit-mapped. On the other hand, little icons and WWW festoons made with a few pure colors GIF- compress (and decompress) very well. Such an image could be doubled in size (height and width) with little increase in file size because it's just about as easy to say "output 500 pixels of color 035" as "output 250 pixels of color 035".
>My question is this-- is this browse infomation incorrect, as I believe it
>to be, or are browser displays different than typical viewers such as LView
>or WinGIf? I have also heard that some browsers limit the number of
>colors they can display to 8, but that affects only the display, not the
>size of the GIF file. If this is true, then I suppose if one created an
>image with more colors in it, they simply would not display, not act as
>though the colors were "used up".
>
>Comments and hard information appreciated. Best, Pamela
>
8-bit GIF is 256 colors, period! If your video card is 8-bit and Windows is configured to 8-bit, then there is a slight problem. Windows does commandeer a small set of colors from the palette for its own use (icons, wall paper, etc.). Therefore, individual applications can have fewer than 256 to work with. Somehow the software accommodates (fudges for) this. Again, if your hardware and configuration support 16- or 24-bit color, you are in fat city and should have no color problems. Walt >Pamela Mason, Chief
>Electronic Information Program
>National Institute of Standards and Technology (NIST)
>Office of Information Services, E-106
>Gaithersburg, MD 20899
>PH: (301) 975-4465
>FAX: (301) 869-8071
>Internet: mailto:pmason@enh.nist.gov
Walter Gilbert, Asst. Dir. mailto:Walter_Gilbert@umail.umd.edu Computer Science Center Manager: Teaching Technologies University of Maryland at College Park 20742-2411 (301)405-6727