Dual ISO setup for excessive red saturation?

[larrycafe]

I was having a hard time shooting scene with saturated red channel.

like my son wearing a bright red jersey playing soccer on concrete field on a sunny day. Or tungsten lighting indoor where ISO 3200 is just good enough with f1.8 and 1/50s

I am not 100% sure if the red channel is totally saturated, but it is hard to bring back the contrast.

in the soccer scene, I should bring down the exposure and saturation a lots, this will give the jersey better looking (not just a flat all red region), however, the face will be too dark.

in the tungsten low light scene, no matter how I change in the white balance setting, the color of skin is still unnatural, either toward orange color, or making it all dull without any red.

I wonder how to setup the dual ISO to help in such scenario. Is it doing negative EC to make sure red is not clipped in the lower ISO, and make a +3 or +4 EV in the dual ISO to get the other channel expose correctly?

[Audionut]

The red channel is less sensitive then the green channel.  It's very hard to blow detail the red channel and not in the other channels.

As a start, if you're using an Adobe product, switch the default camera calibration profile to camera faithful.




I could right an essay on the best way to manage this, but you would be best served with an x-rite color checker passport.

[dmilligan]

From your post it sounds like what you are trying to do is desaturate and/or darken the high red levels like in a bright jersey without desaturating the more subduded ones like skin tones. Is that correct?

You can accomplish this several ways, the easiest I think would be to apply a curve to the red channel only. A curve maps input levels to output levels, so you can bring down the bright reds without touching the lower ones (modify the upper-right side of the curve and leave the left alone). You could also create a layer mask from the red channel for a layer that is more desatured and/or darker than your original and blend it with your original. The layer mask will make it so that the more red a particular area is, the more it gets desaturated/darkened.

I don't think dual ISO will help you with this situation. Dual ISO only helps you capture more dynamic range and you sacrifice a lot of other things in the process (like resolution, increased moire and aliasing). You would only need dual ISO in situations where you would like to brighten the dark shadow areas a lot. The scene and problems you describe don't really sound like the type of situation that would merit dual ISO. IMO dual ISO is a last resort in scenes that you absolutely need to squeeze every bit of DR out of and you can't just take two pics.

[larrycafe]

I see, thanks for all the answer.

I tried the faithful picture style in DPP (where I did not shoot with Dual ISO) and the red is looking better.

and yes, I want to raise the saturation but not want the red jersey to be too saturated.

Tried the fine color controller in Silkypix, and it is good to rectify specific color range without affecting the whole picture.

I will try more with the low light tungsten case.

And by the way, my 60D dual ISO can only go up to 3200, is it hardware limitation? when the base ISO is already 2000 or 2500, the Dual ISO does not look like going up to 6400 or 12800.

[Audionut]

And by the way, my 60D dual ISO can only go up to 3200, is it hardware limitation? when the base ISO is already 2000 or 2500, the Dual ISO does not look like going up to 6400 or 12800.

In a sense yes.  ISOs above a certain point are better accomplished with EV boost in post.

[dmilligan]

ISO above 1600 is more or less just digital, I think on some cameras 3200 is supposedly analog, but it has not been found to make a difference in noise performance (that is certainly my experience, and I do a lot of astrophotography which is all about eeking out every last drop of performance out the camera, I never shoot above ISO1600, and I deal with extremely faint amounts of light).

This means that practially speaking, it's pointless to shoot above ISO1600 as long as you are shooting in raw.Therefore, if ISO 1600 is not enough to blow your highlights, dual ISO is useless (just ETTR). Probably the max useful base ISO for dual ISO is 400. Otherwise you are recovering so little shadow detail that it's not worth the trouble IMO and you still get the negative side effects of dual ISO.

Low light situations are probably the last place you'd want to use dual ISO. You are going to be struggling with noise in the entire image, not just the shadows.

I also have all the digital and extended ISOs disabled (all the ISOs besides 100,200,400,800,1600) all they do is make it take longer to scroll through the ISO list. All these ISOs are applied digitally to the image after it is taken, so there is only the potential for loosing information, not gaining (haha, get it?) it.