H channel modification gives us so many possibilities that it is difficult to know where to start. My usual technique is to get reasonable V and S adjustments, then play around with different techniques until something looks right – or looks as if it has potential, but I run out of ideas. Often many potential results come out of a single image.
Single discrete colours do not really exist in the transform. Depending on the bit depth you are working with, there are either 256 or 65536 colours selectable within the H channel.
As with other manipulations, multiple changes affect each other. This is more noticeable in the colour channel than others as only small colour changes catch our eyes. Often more anchors are called for – or more radical changes which accentuate the oddities for effect.
If you are trying to achieve a specific look – or colour/colour combination then this will direct your experiments as you start with a clear goal, not with an open mind. However be prepared to explore the goal and not only save intermediate curves that trigger other thoughts, but also be critical as to whether or not a goal you were seeking works or not. Many times I conceive an image in my head of what I think the manipulation should be. In reality the results are often not that effective, but a side branch – or change of concept can be.
It is usually best to adjust as the final step (or series of final steps, each giving a different result) before fine tuning.
High saturation makes the H changes more visible.
Fine tuning of all three channels after a pleasing base/first cut has been created is usually advisable. It is in this stage that things become more fluid and the range of permutations begins to get confusing – especially if you have no specific goal in mind. Above all else, remember the old Kiss idiom – Keep It Simple, Stupid.
If there is a simple basic manipulation that you feel is needed after the main adjustments, consider saving the image and applying the change in a fresh application of the color curves transform – or using another transform such as colour correction (or colour balance).
Colour Operations are varied – Inversions, mapping to a small range or single colour, mapping to 2 or more colours, stretching and combinations of these. It is also an opportunity to discuss more advanced anchors as they become necessary to control the manipulations.
The operations discussed here can be applied to other channels, but are usually less effective there.