How can I boost shadows? Using curves to lift shadows would create less contrast in another part of the luma range, so that's not an option. It has to be some form of tone mapping (dynamic range compression), like in raw photo processors, allowing shadows, mid-tones and highlights to be adjusted separately. Any ideas?

(Edit: I guess this should be in the Video Effects board, but it seems impossible to move or even delete this post now...)

I don't quite get what your problem with the curves is, I've managed to use them to boost my shadows with a simple S-shape.

But there is also a 3 point balance effect, maybe that might help you?

Yes the effect „curve“ is the correct one. You can put in 3 points to make an S-curve as you like. Just click into the field with the mouse. Under “channel” you can make it for all RGB colors or for each color separate.

No, an S-curve won't work. Let's say I have a properly exposed subject, and a bright sky, and some deep shadows. I want to lower the brightness of the sky while increasing the brightness in the shadows. If I apply an inverted S-curve, bringing down the sky and up the shadows then the midtones will get severely reduced contrast.
You can google something like "hdr tone mapping".

Example:

Original:


Inverted S-curve to boost shadows and bring down highlights:


Tone-mapped:


It's impossible to make a curve that would take the original and produce the tonemapped output, because 2 pixels with the exact same color in the input image can produce 2 very different colors in the output image, depending on the contexts of those pixels.

Try with „bezier curve“ and “luma”. With Bezier you can put in more points for correction.

Merlimau wrote:Try with „bezier curve“ and “luma”. With Bezier you can put in more points for correction.

I already explained why the curves tool won't work.
A curve maps input colors to output colors. For example you can make a luma curve doubling the value of each pixel, so for example luma 20 will become luma 40. That means that every luma 20 pixel will become 40. Always. No exceptions.

But in tone-mapping one input color can become any number of output colors, depending on the context of the pixel. A luma 20 pixel next to some luma 80 pixels might become luma 25, while another luma 20 pixel next to some luma 15 pixels might become luma 70. (That's what happens in a local contrast filter.) It's impossible to make a curve to increase local contrast.

I showed how the result will look like with a curve. But look at the tone mapped picture. The sky is darker, the palms are brighter, and still there's high contrast in the midtones, too.