Contrast curves vs. fill lights / highlights

[oldmankit]

Hi

There's a question that's been ambling around my brain for some time now. When doing RAW post processing (in Bibble, lightroom etc) my 'default' is to apply a slight contrast curve to the image.

When an image has a relatively high dynamic range, I usually apply highlight recovery and fill lights. But I'm wondering if this is nonsensical, because both controls seem to be doing opposite things. The contrast curve 'spreads apart' the histogram, while the fill lights and highlights 'squash it together'. Would it make sense to get rid of my contrast curve in these situations?

What are other people's opinions on this?

My gut feeling is that I should be using both. Use the contrast curve to increase contrast across the whole image, especially mid-tones. Use fill lights and highlights to control the extremes.

[FrankMi]

I usually address the fill light and recovery if needed as part of the first things I do, then noise and capture sharpness. Changing the contrast level, if needed, is usually one of the last things I do but I'm sure that there are many workflow ways that work for different folks.

[herbert]

Hi Kit,

The histogram shows you where the image has values.

If you use fill light then you are increasing the darks to be brighter. So the histogram changes to have less at the dark end and more towards the centre.

If you use recovery then you are decreasing the lights to be darker. So the histogram changes to have less at the bright end and more towards the centre.

If you change contrast you are spreading out the centre values that are all very similar tones. You want them to have more extreme dark and light tones so you can see the difference, I.e. higher contrast. This means that the histogram centre will be spread out towards the dark and light.

A good way to think about the editing process is to decide what parts of the scene you want to see. The main body of tones should be around the centre. Set this using exposure.

Then adjust the highlights and shadows (recovery and fill light) to bring in as much detail as you would like in the scene, e.g. The tones on a white dress or some texture to the dark shadows.

The final step is to take all your tones and spread them out to make the most of the range you have. This means using the full width of the range from black to white. This is done using contrast.

Of course the amount you do at each step is a choice that you make depending on the look you want. You can always go back and do it again, or make dual copies and compare the results for different developments.

Just experiment and do what you like.

Alex

[AlanP]

When you adjust the contrast of an image look at it as if you have a contrast budget. If you increase the contrast in a tonal range the you must decrease contrast in other ranges. You have to decide how to allocate contrast. Adjusting the highlights or shadows will decrease contrast in the midtones. This will decrease the effect of the curves adjustment.

If you have a high contrase scene such as a landscape with a light sky, midtones in the middle, and shadows in the foreground you cannot make all three high contrast with RAW sliders. In order to get all three you need to make three RAW conversions, one for sky,one for midtones and one for shadows. Combine them in photoshop. When this is done there is an abrupt change in brightness when the scene changes from sky to midtones (same with shadows to midtones) but the image will not look wrong.

Alan

[DanK]

I'd take a somewhat different tack.

The final step is to take all your tones and spread them out to make the most of the range you have. This means using the full width of the range from black to white. This is done using contrast.

This is not correct, I believe. You determine the dynamic range (from black to white) by setting the black point and white point. You can do this with various tools, but the point is the same. Usually, one does this to increase dynamic range, but you can also do it to decrease dynamic range--for example, if you have an image that you don't want to go to full white. Confusingly, the closest LR has to a white point adjustment is the "exposure" slider, while the closest it has to a gamma (midtone ) adjustment is "brightness." This is supposed to change in version 4, I think. I normally do this early on, usually after adjusting WB, but in the case of LR, that is more for me than for the image, as it applies the edits in the end according to its own algorithm.

Contrast does not change total dynamic range. You can think of it as changing the rate at which the image transitions from white to black. A typical S-curve decreases the rate at the dark and light tails, and increases the rate in the middle. This makes near-black tones look darker and near-white lighter, compressing their dynamic range, while increasing the dynamic range in the middle.

Sharpening generally goes last, which is why it is at the bottom of the LR panel.

These adjustments interact in terms of their effect on the overall appearance of the image. One of the many nice things about LR's non-destructive editing is that you can easily deal with the interactions of these things. For example, you might set black and white point to points that are pleasing to you, or fill light at one end or recovery at the other, only to find that they don't look quite right after a later adjustment, such as contrast. You can just redo them be readjusting the slider.

[herbert]

This is not correct, I believe. You determine the dynamic range (from black to white) by setting the black point and white point.

Contrast does not change total dynamic range. You can think of it as changing the rate at which the image transitions from white to black.

I thought that was what I said. Thanks for the additional clarification.

My post was trying to explain why the histogram changes as it does. However I should have pointed out that the exposure and blacks slider set the upper and lower limit of what you want to include. Recovery and fill light manipulate the upper and lower end of tones by bringing them in a bit towards the centre.

Admittedly contrast spreads tones out from the midpoint. With a curve you can map every input level to an output level. Thus you can adjust contrast in specific parts of the tonal range. But increasing contrast, whereever you want to do it, is just spreading out the distribution of tones. That is why the histogram gets fatter and lower.

Alex

[oldmankit]

Thank you to Frank, Herbert, ALan and Dan,

You have each given me information to chew over. I still don't understand this 100%, but I'm getting there.

I will keep experimenting in the light of what you've said, and get back if I have any more q's.

Thanks again
Kit