How to reduce red channel saturation?

[jms698]

I've been having a great time taking pictures with my K20d. I have the custom image set to "natural" (with fine sharpness +1). I find that most images come out great (although often underexposed, but that's another story). However, whenever I take pictures of people in incandescent light the red channel is totally over-saturated. Sometimes to the point of blowing out. Skin looks bright red instead of natural. I have to reduce the red channel saturation in Aperture by about 20 points for the images to look ok.

White balance is not the issue: I set it to the incandescent preset (auto white balance is hopeless in incandescent light, but spot on in other lighting conditions) and tweaking the color temperature in the RAW file makes reduces the red saturation somewhat, but makes all other colors look wrong.

So, is there a way to set the K20d to reduced saturation in the reds, but leave the other colors unaffected? I don't want to have to post-process all my shots.

[jeffkrol]

Originally Posted by jms698

I've been having a great time taking pictures with my K20d. I have the custom image set to "natural" (with fine sharpness +1). I find that most images come out great (although often underexposed, but that's another story). However, whenever I take pictures of people in incandescent light the red channel is totally over-saturated. Sometimes to the point of blowing out. Skin looks bright red instead of natural. I have to reduce the red channel saturation in Aperture by about 20 points for the images to look ok.

White balance is not the issue: I set it to the incandescent preset (auto white balance is hopeless in incandescent light, but spot on in other lighting conditions) and tweaking the color temperature in the RAW file makes reduces the red saturation somewhat, but makes all other colors look wrong.

So, is there a way to set the K20d to reduced saturation in the reds, but leave the other colors unaffected? I don't want to have to post-process all my shots.

Do like in the old film days. Use a tungsten correction filter (bluish) and a custom white balance.
Color compensation filters...: Nikon D3 - D1 / D700 Forum: Digital Photography Review
BTW: AWB doesn't go into the 2600K range that is tungsten.... see your manual.
FILTERS work...
http://forums.dpreview.com/forums/re...ssage=21652561
Nicely done. I convinced myself of this with similar tests years ago, and have long been an advocate of white balancing filters.

[Marc Sabatella]

Originally Posted by jms698

White balance is not the issue: I set it to the incandescent preset (auto white balance is hopeless in incandescent light, but spot on in other lighting conditions) and tweaking the color temperature in the RAW file makes reduces the red saturation somewhat, but makes all other colors look wrong.

You don't say what RAW processing program you are using, but WB *is* the issue. If the red channel is clipping, or otherwise dominating the shot, then WB temperature is not set low enough. Apparently the incandescent prese tisn't matching the color of your bulbs well enough. Either customize the wb (using manual wb, or using the in-camera controls to alter the incandescent defaults - at least, I think the K20D supports that), or create a custom wb in your PP program and hit whatever button it takes to apply that present to all your tungset shots (and if takes more than a button press or two to apply a given wb preset to a whole bunch of photos at once, you're using the wrong RAW program).

[georgweb]

jms,
something strange with your avatar, blown white balance maybe :-)

The links that jeffkrol posted are recommending what he said, use a light blue filter (80A,80B) on your DSLR.

I am wondering wether you can achieve the effect of that filter with manual white balance. The linked posts say No for a daylight-WB-optimized DSLR.

Actually I have such a blue filter from the film days cause it was the only thing that helped for my frequent stage shootings.

And yes if I just shoot RAW (+WB tungsten is the coolest I can get) and then push into the blues in PP, all other colors go blueish. Especially black clothes get very purple.

So, I will try next time manual WB on some reddish stage lights or whitish surfaces lit by those lights (+RAW). And I'll take the blue filter, but it is only 55mm and the lens is 86mm :-) And it will eat another stop of light. Do I need a fullframe easy peasy 3200ISO DSLR? ДڪЖڮЮڴ☼њ♣♫

Here's what it looks like with RAW+tungstenWB with PP-corrected skins (that is the best I could get, originally the faces are red smudge). K100D with 200/2.8 lens. Of course dimly lit stages with yellow-reddish lamps are not of benefit :-(

[Wheatfield]

Originally Posted by georgweb

jms,
something strange with your avatar, blown white balance maybe :-)

The links that jeffkrol posted are recommending what he said, use a light blue filter (80A,80B) on your DSLR.

I am wondering wether you can achieve the effect of that filter with manual white balance (the linked posts say no on a Nikon DSLR, or a daylight-WB-balanced DSLR for that matter)

Actually I have such a blue filter from the film days cause it was the only thing that helped for my frequent stage shootings.

And yes if I just shoot RAW (+WB tungsten is the coolest I can get) and then push into the blues in PP, all other colors go blueish. Especially black clothes get very purple.

So, I will try next time manual WB on some reddish stage lights or whitish surfaces lit by those lights (+RAW). And I'll take the blue filter, but it is only 55mm and the lens is 86mm :-) And it will eat another stop of light. Do I need a fullframe easy peasy 3200ISO DSLR? ДڪЖڮЮڴ☼њ♣♫

Here's what it looks like with RAW+tungstenWB with PP-corrected skins (that is the best I could get, originally the faces are red smudge). K100D with 200/2.8 lens. Of course dimly lit stages with yellow-reddish lamps are not of benefit :-(

The fix it in post have got it wrong in my experience. Sensors are "daylight balanced" in their native colour sensitivity range. You move outside that range, and white balance will pick up the slack to a point, in much the same way that with film, the printer could give you a reasonably acceptable print in some situations where you moved outside the film's spectrum of acceptability.
Move to far away from what the camera can accommodate, and you will likely never be able to get an acceptable white balance.

Colour correction filters still have a place in the photographer's kit. You can usually get an acceptable RAW conversion most of the time with white balance adjustment, but you will always get a better one if the light hitting the filter is as close to daylight as you can manage.
My filter kit still has both an 80A and an FlD filter in it for this reason.

[creampuff]

Use an Expodisc or similar product and do a manual white balance reading.
I have found it to be pretty accurate. The WB reading will only be accurate so long as the lighting doesn't change. If it does, then you'll need to take another custom WB reading.

[Marc Sabatella]

Originally Posted by Wheatfield

The fix it in post have got it wrong in my experience. Sensors are "daylight balanced" in their native colour sensitivity range. You move outside that range, and white balance will pick up the slack to a point, in much the same way that with film, the printer could give you a reasonably acceptable print in some situations where you moved outside the film's spectrum of acceptability.
Move to far away from what the camera can accommodate, and you will likely never be able to get an acceptable white balance.

True. But the problem with colored filters is that most of the situations we are talking about here involve low light levels as it is. A blue filter means it's going to be that much hard to get enough light at all. Of course, one could question whether bad light is better than no light. But I do find that if nothing else, the red channel on its own often makes a fine B&W conversion.

[jeffkrol]

Originally Posted by Marc Sabatella

True. But the problem with colored filters is that most of the situations we are talking about here involve low light levels as it is. A blue filter means it's going to be that much hard to get enough light at all. Of course, one could question whether bad light is better than no light. But I do find that if nothing else, the red channel on its own often makes a fine B&W conversion.

If your going to convert to B&W, losing a stop or 2 of light is somewhat meaningless.
Interesting reference article(s)
White Balance -- Are you RGB Savvy by Moose Peterson
http://www.pochtar.com/NikonWhiteBalanceCoeffs.htm
The dirty secret of WB and pseudo-ISO pushes, and the solution: Nikon D3 - D1 / D700 Forum: Digital Photography Review
When you use a color compensating filter, you suppress the dominant
frequencies of the light, holding them back so they don't overexposure as
you gather the frequencies that *are* underrepresented. High altitude has
too much blue; daylight, too much green; incandescent, too much red.
Choose a color-correcting filter of a density that works for your camera
and light. I believe that Julia has suggested CCM20 may be enough on a D2H
for daylight work, but other numbers for other bodies.

Color Temperature and Color Correction in Photography
http://www.pochtar.com/NikonWhiteBalanceCoeffs.htm

So yes, Jim, you're right: this means a longer exposure. But by color-
correcting your light before it hits your camera, you'll get real data,
not false data created by amplification.

And you might not lose a full 2 stops. True, with a blue-admitting filter,
you'll pay more in exposure because blue contributes least to human
luminance perception, The precise density you'll need varies according to
your model's CFA dyes and shooting light. Maybe an 80A's 2 stops; maybe an
80C's one stop or an 82C's 2/3 stop will suffice to put you where digital
amplification won't cause too much noise.

[Wheatfield]

Originally Posted by Marc Sabatella

True. But the problem with colored filters is that most of the situations we are talking about here involve low light levels as it is. A blue filter means it's going to be that much hard to get enough light at all. Of course, one could question whether bad light is better than no light. But I do find that if nothing else, the red channel on its own often makes a fine B&W conversion.

True enough, but we were able to do it with 400 ISO film, and since with digital, 1600 is the new 400, so we gain a couple of stops advantage.