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Minerva
Head of Runboard staff

Registered: 11-2005
Posts: 9597
Karma: 132 (+147/-15)
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posticon FAQ: What affects image file size?


If your message board contains images with large file sizes, it can take forever for dialup users to load the pages.  The longer people have to wait for a page to load, the more likely it is that they will give up and leave, never to return.  So beware of large animated banners, because what "looks cool" to you might actually be chasing a lot of people away from your board.

The obvious solution to this is to avoid using a lot of images on your board that take forever to load, which means using images with smaller file sizes.  That said, what determines an image's file size?  Read on to find out...


Image dimensions:

Generally, the smaller the actual width and height of the image, the smaller the file size.  By actual, I mean that using width="48" height="64" to resize an image that is actually 96×128px is not going to decrease the file size, and will only make it look smaller on the page.  To clarify, using code to resize images will not speed up its loading time, so the image must be resized with an image editing program before uploading and using.


Number of frames in animated gifs:

Animated gifs are larger than non-animated images of the same dimensions, because each frame of an animation also adds to the file size.  With animated gifs, the dimensions as well as the number of frames both help determine the file size.


Number of colors:

Dimensions are not the only thing that determine a image's file size, either, as the number of colors in an image also affects it.  For example, the happy smiley (emoticon) is 93 bytes, while the tongue smiley (emoticon) is a bit larger at 103 bytes.  Notice that the happy smiley uses two colors, yellow and black, while the tongue smiley uses a third color, red, for the tongue.


gif, jpg, or png?

Choice of file format also affects file size.  If your image has very few colors, such as with the aforementioned smilies, gif is usually more appropriate and will normally result in a smaller file size with the way it indexes colors.  For more complex images with more detail such as photographs, png will give you the best quality, but jpg will give you a smaller size while still looking better than gif.

jpg and png offer compression, while gif offers indexing.  The more you compress a jpg or png or the fewer colors in gif indexing, the smaller the file size, but the more you compromise quality (unless a gif truly only has two or three colors).  The best way to know what works the best is to save an image in various formats using various compression and indexing, view the image for quality, and check the properties to find its file size.

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7/7/2006, 2:34 am Link to this post PM Lesigner Girl Read Blog
 


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