Saturday, July 30, 2005

Graphics File Formats

WARNING: This blog entry was imported from my old blog on (which used different blogging software), so formatting and links may not be correct.

I get screenshots every now and then in the mail, and frequently in bad formats, so perhaps the following is not known to all:

  • Do NOT send BMP files! They are uncompressed. A simple screenshot, which should be a something like a 50k gif, will be a 5 megabyte attachment - 100 times larger than necessary! Unfortunately, BMP is what you get by default when you grab screenshots with Ctrl-Printscreen
    in Windows and paste it from the clipboard. TIFF, common on the Mac, suffers from a similar bloated file size problem since it too typically
    is not compressed.

  • Do NOT use JPEG for screenshots! Unless all compression is turned off (which it never seems to be), JPEG is a spectacularly
    bad format for uniform color surfaces like those you get from application screenshots. JPEG is great for photos - much better than GIF or PNG.
    But for screenshots it introduces all kinds of ugly visual artifacts.

...and finally, a related issue: If you're going to show a scaled down version of a picture in a web page (e.g. a thumbnail),
don't just use the width and height attributes on the image tag! Not only does that require the full image to be downloaded anyway,
but worse yet, most browsers do a horrible job scaling pictures. Prescale the picture in an image editor instead.


  1. On windows, I am using a nice free tool, Gadwin Printscreen. It permits to choose the format (bmp, jpg, gif, png, tif, tga), to resize the capture, ...
    A very nice tool.

  2. Just as an FYI ... the new Mac OS X release (Tiger) saves screenshots as PNG files, which is pretty useful. :-)

  3. Regarding PNG on Tiger: I'm running Tiger on this laptop, and I don't see that. When I use the Snapshot application to grab a screenshot, and invoke Save, I get a filename dialog without a toggle to choose any other formats, and when I look at the file saved it's a .tiff.