Skin tone info for group shots

asamuel

So faces must be more yellow than red lest they look sunburnt.
Asian skin approx 10%-20% more yellow than red.


However things become more complicated with multiple people.
Consider the reading from a picture taken with 5 chinese models:

LAB A (B/W point brought in 10) B (B/W brought in 15)

Therefore steeper yellow.

X5 people

1) M 39% Y32% 2) M 42% Y41%
2) M 58% Y 57% 3) M 69% Y 100% 4) M47% Y54%


Questions
1) Should this be rectified with masks and multiple layers? or a happy medium?

2) Where on the body is best to take the reading of colour info? Where on the face? other parts of the body? Hands for example give a higher yellow than magenta across the board.

BinaryFx

Hi asamuel, good questions!

I would need to see the image for better comments.

Avoid faces if possible, even without makeup they can mislead and the same goes for lighting that may put the area into shadow or blow it out.

I try to go for a large area if possible, in the centre - to average things out. Even when using 5x5 sample info readings, it can sometimes help to dupe the image and blur it a bit.

It also helps to take many sample readings.

So, for a basic caucasian skintone, the cyan value would range somewhere between 1/4 to 1/2 the magenta value (lighter tans have less cyan). The yellow value is often a bit heavier than the magenta in ratio for a pleasing tan.

So for a basic asian ratio (but there is a lot of variation in asian skin tone, and China has many racial groups etc) - I would look at slightly higher cyan and yellow values when compared to a good caucasian tan ratio. Even though yellow is the weakest ink, it is amazing what a 5-10% +/- change can make in skintones, for good or bad! The cyan is often more critical than the magenta and may need special work.

Even though CMY ratio is being discussed, this obviously works in RGB. One can set the info palette in Photoshop to display the RGB values in CMYK or one can learn to evaluate the ratio of R to G to B in their particular RGB working space.

Best,

Stephen Marsh.
http://members.ozemail.com.au/~binaryfx/

pathfinder

Good advice.

When I try to read the data on skin it tends to vary quite a bit on the same individual. I prefer readings on the lower neck, front or back, or on the back of the hands. If they are right, the facial colors seems to be acceptable. I am not a pro printer here so take this with a grain of salt.

rutt

Group shots can be challenging. I go though a little mental questionnaire.

1. Mixed cast? Is there any reason to think that different light sources are at play, requiring a non-uniform approach to the shot?
2. Shadows and/or highlights? If the lighting isn't uniform, you may need to do something early to even things out.
3. Make up? As has been noted, Women's faces are not the most reliable place to measure for the CMYK fleshtone rules.
4. Different complexions? Very light skinned people often require different approaches from darker skinned people. In particular, Darker skinned people need a stronger dose of magenta to balance the heavy yellow. Lighter skinned people often need some sort of strong blending to bring out their facial features. The same treatment may send darker skinned faces deep into shadow.

Each of these issues can lead one to a some different variation on the basic portrait recipe. Use either the A or B channel as a (possibly inverted) mask for curves for 1. Consider the shadow/highlight correction for 2. Find sample points on the neck and shoulders for 3. Consider either RGB curves or A and or B channel masks for 4.

LiquidAir

I recently was correcting a group shot where some (but not all) of the faces were too red. My trick was to use the burn tool on the A channel in LAB color. You can use this trick for many kinds of local color correction. Select the channel you want to modify but make sure you are viewing full color. Pick either the burn or the dodge tool as appropriate and dial the exposure down to 10% or less; you likely don't want to move the color very far.

Burn in the A channel pushes the color toward green.
Dodge in the A channel pushes the color toward magenta.
Burn in the B channel pushes the color toward blue.
Dodge in the B channel pushes the color toward yellow.

edgework

LiquidAir wrote:

I recently was correcting a group shot where some (but not all) of the faces were too red. My trick was to use the burn tool on the A channel in LAB color. You can use this trick for many kinds of local color correction. Select the channel you want to modify but make sure you are viewing full color. Pick either the burn or the dodge tool as appropriate and dial the exposure down to 10% or less; you likely don't want to move the color very far.

Burn in the A channel pushes the color toward green.
Dodge in the A channel pushes the color toward magenta.
Burn in the B channel pushes the color toward blue.
Dodge in the B channel pushes the color toward yellow.

All correct, but dangerous, as you are "hardwiring" your modifications. Using curves with the "Blend if" sliders can give the same precision in targeting specific areas of the image, but with much more flexibility.

asamuel

this has been a rewarding enquirey that I have been able to follow.

just great. I have followed the basic advice of reading other darker flesh areas, neck back of hands. this has helped but there is some imbalance. Whilst I havent used the more involved recommendations its only because I dont want to spread myself to thinly.

this has been an excercise in building for the future.

pathfinder

LiquidAir wrote:

I recently was correcting a group shot where some (but not all) of the faces were too red. My trick was to use the burn tool on the A channel in LAB color. You can use this trick for many kinds of local color correction. Select the channel you want to modify but make sure you are viewing full color. Pick either the burn or the dodge tool as appropriate and dial the exposure down to 10% or less; you likely don't want to move the color very far.

Burn in the A channel pushes the color toward green.
Dodge in the A channel pushes the color toward magenta.
Burn in the B channel pushes the color toward blue.
Dodge in the B channel pushes the color toward yellow.

I posted some images demonstrating exactly this, last year in our discussion of LAB:The Canyon Conundrum book.

Here is a barn that I have burned 15% ( for emphasis) in the a or b channel as labled.



Here is an example of using the dodge tool at 25% in the a or b channel - It is better to do this in an adjustment layer so that the Opacity slider can then be used to fine tune it.

DavidTO

Another problem with faces is the fact that digital cameras are sensitive to near infra red, and the capillaries near the surface of the skin on those with "ruddy" complexions make it nearly impossible to get one correction that will work with other faces. Like my father and my son, for instance. Especially with a flash, I've found.