I have a basic understanding of curves. That is, I know the mathematical concept behind them, and I have an idea what happens when I change them. But this knowledge came from sources which assumed that I am working with an image editing programm like Photoshop/Gimp.
The sources also teach beginning enthusiasts like me to do as much as possible in RAW, to prevent information loss in the image. So when I saw that the raw tool I use has curves, I decided to try using them there instead of later in Gimp.
I am however mystified by the presence of two different curves in ufraw. They are described as follows in the user guide:
Base curve imitates the functionality of Nikon's tone curves. For Nikon NEF files you can choose Custom curve if you want to use the curve that is embedded in the raw file. Choosing Camera curve will enable the embedded curve only if it was enabled in camera. All camera users can load curves to apply custom curves to their images. The famous white wedding curve (V3.5) from Fotogenetic was applied to the image on the right. Move the mouse over the image to see the original image with a linear curve. A +0.5EV was applied to the original image to equalize the luminosity of both images. The white wedding curve adds some details to the dress. UFRaw can directly apply The curve from Fotogenetic to your images.
The base curve is applied directly to every color channel. It is applied after the exposure and white balance setting so that it will effect each channel equally. It is applied before the gamma correction, meaning that it is applied on the linear data.
and the second one
The curve in the Corrections settings is applied to the luminosity channel in Lch(ab) space. The controls on the left of the curve editor are for controlling the black point. You will notice that they simply control the leftmost point of the curve. If your picture looks foggy, the auto black button Auto Adjust might fix it. The auto curve button Auto Adjust on the right tries to set a curve that flattens the histogram. It can add lots of contrast to your photo but sometimes the results look very artificial.
I don't know where to get tone curves for my camera (a D90). I don't know how to make my camera embed a curve in the RAW file either.
My question: When I want to change the way my photo looks, which curve should I use for what kind of change?