Quote - So I repeated the experiment, in Paintshop Pro instead. Surprise! No banding. No dimples. Well, it's there though, after a very close investigation (take difference, and increase brightness to +100 and contrast to +60 in an additional adjustment layer). But the dimples are less deep, and about 4 times wider spaced.

I don't know what PaintShop does, but you can get rid of the color bands adding random noise with levels less of 1/256. With the same method you can produce 16 bit color (65K) that look similar and without banding as true color 24 bits (16M). Adding random noise reduce the artifacts but increase slightly the file size. You can do many things with software.

Telling that an image was saved as #12 is meaningless, I don't use Photoshop and the level 12 is basic Chinese for me. JPEG format allows to set different parameters for the compression, you not only can set the amount of compression, you also can set the color bandwidth reduction scheme. It looks as PaintShop Pro is much flexible than PhotoShop and allows you to set different compression schemes.

No matter how are your settings, always something is lost due the compression, even the quality is set to the maximum of the maximums.

One important to take into consideration is that mp3 and jpeg are subjective compression methods where something is lost forever. What was lost is as the name tells. is subjective and so it depend on the person that see or hear the compressed data.

In the extreme, a blind person will not see any difference between a color and a black and white image. For him all is the same and nothing was lost removing the color information and if you insist that the images are different, if he is a rude person, he will reply f*&*# y@! and all the classic known bla bla bla.

It was an extreme example, a blind person see nothing and so he is unable to see any difference. In normal cases, one person do not see or hear the same as other. Some people has more acute sight and perceive more than other and also your vision capabilities improve with training and use. With age you can lose your vision due to some disease, but even with this you perceive much more than when you was young. NOTE: A blind person with some training can tell you which image is in color and which is B&W.

What to do? A simple rule. Save the image in png and jpeg, if you see that the saved png image looks better than the saved jpeg image then discard the jpeg and keep the png. If you perceive no difference then you can save in jpeg. In professional work where the target audience requires high quality you always must save in png of tiff even you don't see any difference. Remember that your client can have a much better perception than you have and he is able to see differences that for you don't exist.

Stupidity also evolves!