because I do alot of painting on the computer (using painter 11 and artrage) as well as traditional oil paintings, i´ve come to realize my biggest sticking point.... VALUES. The differnce in the range of values you can produce on a computer and with oil paint is incredible. I have no way to judge this of course but in my humble opinion it seems to be about half in paint compared to digital.
This means where I´m used to working with my 9 value scale in painter (and to which I´ve become quite fond) when working in paint its more like using values 4 to 9 (white being 1) i seem to always key my painting wrong because of this, especially when working from photos (which I view digitally on my pc, as I´ve no printer)
Sometimes I remember and put in my lightest light very early and key the painting to that but when i forget I end up wasting time going back and changing all the values in the painting, what a waste of time and paint.
An interesting note on keying your paintings and values, the darker your overall image the less change in value of dark tones is needed to have significant contrast. the same is also true of light paintings only this time concerning light tones. hmmm is that confusing...it´s diagram time!
In the above diagram we have three 9 value scales one on mid grey one on black and one on white. now notice something strange about this, The number 2 value on the middle scale seems to be much darker than the 2 value on the top scale. This is because all values seem darker against a light background, the scale seems bunched to one side as if most of your values are in the lights and all the darks are very close together. knowing this means you can change one prodominate value in a painting and effectively change the whole image with this effect (in theory, im too tired to root out an example right now, maybe tomorrow i´ll follow this up)
so pay close attention to all your values they the most important part of the painting in my opinion.