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Author Topic: Comparison of image formats  (Read 24840 times)

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Dilbert

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    Comparison of image formats
    « on: April 02, 2006, 05:27:34 PM »
    Question
    What format should I save my pictures in?

    Answer
    The real answer is that it depends on what you are trying to save. In any case, this article will cover the different file formats and discuss the strengths and weaknesses of the file types. For examples, I will use a Paint image with most of the colors selectable on the standard tray.

    Note
    I am familiar with Windows formats, but not any formats on other operating systems. If any information is different/not present on another operating system, please PM me and I will add it to the list. Thank you.

    24-bit Bitmap

    Bitmap (.bmp) files cause absolutely no dithering at 24-bit and no loss of color. They keep even the minute details in place without a change. The image I created in Paint, saved as a 24-bit bitmap:

    http://img349.imageshack.us/img349/8254/test2tc.png (284 KB)

    So what's the downside of the 24-bit? The big one would have to be the size. 284 KB is a big file for something so small. So when is it a good idea? Well, some games use a specific color as a "transparency", meaning anything of that color is invisible. For example, in Civilization it's a shade of pink. Even the slightest dithering will cause a messy pink background. So if you're editing game images, .bmp is the way to go.

    16-color bitmap

    An obsolete format, this is similar to the current .bmp in that it is non-dithering. However, your choice of colors is somewhat limited.

    Notice the difference between the 24-bit and this:

    http://img349.imageshack.us/img349/3086/copyoftest7ii.png (47.8 KB)

    It's a trade-off of sorts; you get less colors but a major size improvement. Notice the 47.8 KB to the 284 KB of the 24-bit. If you don't need those colors (how you figure that out is beyond me) than this can work well for you.

    256-color bitmap

    This format is a compromise between 24-bit and 16-color. It causes color loss, but as you'll notice, it's less severe:

    http://img91.imageshack.us/img91/3528/copyoftest9xb.png (95.7 KB)

    In every way, it's a balance between the two. Less color loss, but not perfect; less file size, but still not great; it's an "in the middle" format.

    Monochrome bitmap

    The last of the bitmaps, this format is the monster. It deals in two absolutes: black and white. Nothing inbetween. Good, I suppose, for making fake old pictures from the days of black and white cameras, but otherwise almost useless.

    http://img327.imageshack.us/img327/2702/copyoftest3ke.png (12.1 KB)

    ImageShack automatically converted it into a PNG file, but it is indeed an uploaded bitmap. Note the file size, but be wary of the horrible quality of picture.

    JPEG

    Often touted as the "smallest of the file formats decent for hosting", it has color loss based on how much it is compressed; the more compression, the more the color loss. However, you pay for that with a high amount of dithering. It's not noticable in high-quality images taken by a good camera, but this Paint image became a mess:

    http://img85.imageshack.us/img85/4991/copyoftest9iy.jpg (10 KB)

    Indeed, a very small file. Use it for high-quality pictures where the dithering won't be noticed as much, but stay away from it for an image like this. JPEGS are, however, good for saving CMYK channels (see below)

    Graphics Interchange Format

    GIF files are excellent formats in the way that they cause no dithering like JPEG's do. Also, they are the only format suitable for animation. All animated single files that are non-video (in other words, all animated files that can be opened in Paint) are in the GIF format. However, although color loss is nonexistant in basic coloring, there is a sort of plaid texturing to the more "advanced" colors:

    http://img327.imageshack.us/img327/1305/test9ju.gif (8.41 KB)

    This is because GIF files are subject to a 256 color limit.

    TIF/TIFF

    TIF(F) files are noted for their small file sizes, minimal (if any) dithering and color loss. Ideal for simple pictures; however, the file size tends to sharply increase with more complicated pictures. Again, ImageShack renamed the extension of this .TIF file.

    http://img401.imageshack.us/img401/339/test2tc8zh.png (27.8 KB)

    TIFF files are much more readily accepted by a printer, because they make it possible to save CMYK channels. TIFFs are also subject to compression levels (the picture you see is uncompressed), and therefore quality is not absolute; however, most of the time TIFF files will not be compressed unless you specify this.

    PNG

    PNG files are another excellent format for images; they tend to be smaller than JPEG's, and have little or no dithering and color loss. PNG allows for Vector drawing.

    http://img159.imageshack.us/img159/1407/test2aw.png (4.56 KB)

    And the winner is...

    PNG, with a good quality picture and smallest file size of any out there. If you have been using JP(E)G to get small files, consider PNG instead if you can. It makes an excellent choice for pictures. However, it should be noted that PNGs tend to be larger than the average GIF. However, if you have a quality picture, the extra file size may be worth it. It's your call.

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