Senior Computer Tutor Don Edrington
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Comparison of JPG and GIF Image Files

I've been asked about the differ-
ences between JPG (Joint Photo-
graphic Experts Group) pictures and GIF (Graphic Interchange Format) images.

The JPG image format has become the de facto world standard for copying images from a digital camera onto a computer's hard drive, and is the most-used format for displaying photos on the Internet.

Earlier image formats, such as RAW, TIF, and BMP, generated huge file sizes that took up lots of disk space and which were difficult to transmit as email attachments.

Admittedly, large file sizes were more of an issue back when disk drives were small and getting online was usually done via slow telephone dial-up connections. Nonetheless, folks still have various reasons for wanting to reduce the file sizes of their photos and other images.

JPG images have smaller file sizes because of "compression," which usually discards about 20% of the color information in a photo. This information tends to be redundant, and the 80% left over is normally adequate to be visually pleasing to the eye.

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However, if you open a previously-saved JPG and then save it again, the new image's file size is likely to be about 80% of the first 80%. Subsequent opening and saving of a compressed file will continue to discard information to where the final image may look mushy and out of focus. Once information is removed from a JPG there is no way to restore it.

Nonetheless, this problem can be circumvented by maintaining your JPG at its original "digital camera file size." If you want to edit the picture, open it in an image-editing program, go to File>Save As, and give it a new name. The original will then be set aside as you work on the copy. If you subsequently decide to open the copied image for more editing, do File>Save As, and give it yet another name. Using incremental names, such as Bob-1.jpg and Bob-2.jpg makes this easy to do.

You can also opt to save subsequent copies of an image at a "Save Quality" of 100%, or at any percentage of your choice. In Irfanview (free from this feature pops up in a dialogue box when you do File>Save As.

Another option under File>Save As is "Save As Type," where you can choose a non-compressible format, such as BMP or TIF. You can edit BMPs and TIFs without fear of losing any of their color information. Finally, re-save the edited file as a JPG.

You could also choose the GIF format; but photos limited to 256 colors are usually less satisfying than JPGs that can contain millions of colors. However, there is still a place for 256-color images on the Internet. Most of the cartoons and other simple graphics seen online are GIF files, including most of the cute animated ones.

Regarding "compression," many types of files can be reduced in size, and subsequently restored to their original state. This is often called "zipping" and "unzipping;" but such is not the case with JPG compression.

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