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The Basics: File size

File size is important when you are trying to make an image available on-line because it has to be good quality enough that it’s useful, but small enough that it can be loaded into a browser without having the patron wait. Also, if you want to archive the images, then you want a high quality archival image without being too hefty on memory.

There are a few things that affect file size:

The type of file affects file size. See the post about file types.

Whether you are saving in full color, grayscale, or black and white also affects it. Typically, full color images are going to be large files. Grayscale is slightly smaller, but still much greater than black and white. However, you have some options when saving in full color or grayscale.

8 Bit or 24 bit Color/Grayscale

You can save a color or grayscale image as either 8 bit or 24 bit color or grayscale.

8-bit
8 bit means that there are 8 bits that describe each pixel. This means that you have 256 different combination of bits to show 256 different colors (or levels of grayscale).

For most images, 8 bit color and grayscale should be enough.

24-bit
24 bit color (Also known as True color), gives 24 bits of information per pixel, meaning that there are 16,777,216 different colors that each pixel can have. While this gives you the greatest range of color, it also makes the file size much greater.

24 bit color is useful if you need a very accurate reproduction of color.

1-bit
Black and white is essentially 1 bit color. It means that there is only one bit of information per pixel, and that information is either a 1 or a 0 (either white or black). This is the smallest file you can have, and is perfect for clear text.
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