Compression

Ween · 01-31-2004, 06:52 PM

I'm new to digital photography (well, photography in general), and I'm a little confused as how compression relates to image quality. I use a Nikon CoolPix 2100 which lets you choose image quality of High (1600x1200 JPEG 1:4 compression) or Normal (1600x1200 JPEG 1:8 compression).

When I look at the EXIF info, pics taken at the High setting say it has compression of '4 bits/pixel,' and pics taken on the Normal setting say compression is '2 bits/pixel.'

I thought more compression equals less detail. If so, how does having 4 bits of compression per pixel (High) as opposed to 2 bits (Normal) lead to higher quality? I've noticed no difference in image quality between Normal and High setting, except file size is about twice that in High as it is in Normal.

And on an unrelated note, do the type of batteries you use have any effect on your photos? I know that sounds dumb, but since I switched from the CRV3 batteries to NiMH rechargable ones, my photos seem to be getting worse. I'd like to think that over time, one would get better at a particular skill, but I seem to be backsliding. The only variables that have changed are the battery type and the image quality setting. Weird.

Any help would be greatly appreciated (and I'm not looking for "Get a better camera" type help...unless you want to send me some cash!!!). Thanks!

Ween · 02-02-2004, 04:24 AM

Uh, yeah, thanks for all the help...

ddavies · 02-06-2004, 09:25 PM

To simplify compression a great deal, what the compression program is doing is taking a square sample within the image, and trying to make all the values in the sample the same value.

The more the compression, the more you will begin to see artifacts of the compression (8x8 pixel boxes) within the image.

You can look up the most common compression for photographs (jpeg) in a dictionary or online encyclopedia.