Originally posted by David Ey:
Also, at what quality setting did you set camera? It seems when I use a lessor quality setting AND crop the shot AND reduce it for entry I get a picture that looks like it has a swirrled woodgrain or was painted with finger paints. Is that what causes this in some of the entries? |
I think you are describing an effect called banding, which usually shows up in smooth gradients. I believe that part of the compression process may eliminate some tones, so that (for a simple example) areas of 49%, 50%, and 51% would all be assigned a 50% value, giving a broader area of flat tone. The neighboring area may be be 46%, 47%, and 48% and be "flattened" to 47%, producing a perceptible margin.
The effect can also be introduced by resampling the image. If a gradient originally spans 600 pixels, and you have to reduce the size of that area to 200 pixels, there aren't as many pixels available to reproduce all the values.
You can produce this effect on any printer. Create a gradient and print it with a halftone screen of 60 LPI (lines per inch) and you should get a smooth gradient of tones, but with large, visible dots. Print the same page with a screen of 150 LPI and you'll see the bands, although the individual dots are now fine and less obvious. |
