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  3. January 2007

Re: What format for save-as on a scanned photo?




What format for save-as on a scanned photo?

What format gives the best quality of scanned & saved image?



A few considerations related to image quality:

WHY NOT JPEG?
The JPEG format has a "lossy" compression scheme. That means that it actually drops details from the picture as part of it's compression of the data, causing poorer image quality.
The lossy compression in JPEG is designed for photographs (as opposed to line art, or cartoons, or other image types where you might have relatively few colors and crisp, well-defined lines.) So it's not as bad with photographs as it could be with other types of scans.
This lossy compression can be turned off (it's an optional feature of the format) if your software supports the disabling of it. However, most graphic design people prefer to use a different format for their master copies to avoid the potential for the loss.
Then, when deploying to a web site or other means of distribution where a smaller-sized image is preferred, the master picture would simply be converted to JPEG. That way, the compression is only done once. 


KEEP THE COLORS HIGH
A few older image formats (Grayscale BMP, GIF format, etc) are limited in the number of colors they support. Reducing the number of colors will drastically reduce the quality of your picture, but will make them take up less space.
For the master copy of your images, it's best to use a format that allows a high number of colors. Modern BMP/DIB format allows for 24bit colors, as do PNG, TIFF, and JPEG. However, some people will avoid DIB/BMP because of the historical 8-bit (256 color) limitation.
My experience is that the main two formats to avoid are GIF and JPEG (JPG). Other than those, all of the raster image formats basically work the same. There's really no advantage to GIF anymore, anyway... PNG has all but replaced it.
JPEG is still great when you need lossy compression to get a very small image size without reducing the number of colors. But shouldn't be used for the "master" copy, only for the finished product.

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