What are the technical details that make turning black skin to white difficult?

[PSKer]

I am not that advanced in my editing skills. But I can change the color of a dress, replace the head, correct a skin tone and texture, remove lens flare, and stuff like that.

I have been trying to find an easy and straightforward way to turn black skin into white, but couldn't understand why technically there doesn't seem to be an easy way. I mean what in the color details that make this look impossible given the advanced tools we have in photo manipulation programs like PS.

Among what I tried is using a gradient map layer putting the desired color in the middle and moving the slider to the left. I tried putting the desired color on the left. I tried the colorize option in hue/sat. layer. I tried solid color layer with hue and color blending modes. I tried curves layer to brighten the skin first and then applying a gradient map, hue/sat. or solid color layers.

I also tried extracting the white skin color from the black skin color, and then adding the extracted color over with a linear dodge (add) blending mode.

Nothing worked.

I have no other purpose, but I'm curious, what is it in the color details that make turning black skin into white such a complete job?

[davescm]

Sorry that you found them irrelevant. They were there to show what you should be aiming at is adjusting the luminance and saturation but leaving the hue unchanged. You can do that with curves and appropriate blending modes.

Dave

[PSKer]

I agree on that.

[D Fosse]

Those article very directly and precisely answer the question in your original post.

If you feel they don't, you may need to rephrase your questions, because then we have all misunderstood. Which I sort of hope, since changing people's skin tones is obviously sensitive and something you should be careful with.

[PSKer]

Dave who gave me the articles as well as Conrad who gave the the guidance did not misunderstand my post. In fact, Dave agrees that the articles aim at teaching to adjust the luminance and saturation and to leave the hue unchanged when it comes to skin. They don't tell how to change the skin color. Don't you also agree?

Besides, I didn't ask how to change the skin color. If you pay attention, I was mainly curious, what is it that makes changing skin color so difficult and not straightforward. But as an appreciation for Conrad's effort and for bringing me close to achieving it, and because technically, no one else answered my question, I selected his reply as a best answer.

Also, since this issue was addressed in more than a reply, I see no ethical problem in changing skin color, whether from black to while or from white to black, because I'm trying it only as part of my learning this art of photo manipulation among all sorts of thing that've been trying out. And if in the future I'd do it for someone, it wouldn't be their approval.

I have friends who send me their photos and ask me to surprise them. I know them very well. And I know that even when they don't like something, they'll just tell me about it without feeling upset or offended. One of them, I changed her hairstyle, and she didn't like it. But she sent me another photo of her to edit. And when I did, she told me I'm a good artist.

[Conrad_C]

…I was mainly curious, what is it that makes changing skin color so difficult and not straightforward.

By @PSKer

Do you think that the example I posted was not a convincing color change? If you do think it’s convincing, then there is no more question…the example showed that it is easy (two quick layers), if you know how.

If you think my example is not convincing, then is the question actually “Why is it difficult to make a skin color change convincing?” or “Why is it difficult to figure out how to change the skin color convincingly?” If so, then there may be more answers.

If the assumption is that all you have to do is change the color, then how can that be so hard, right? (In my example, changing the color was easy because all I did was sample the lighter skin color.) But maybe the problem is that changing color alone doesn’t look right. That means other problems need to be solved too, that changing just “color” was too narrow of a question.

For one thing, remember that it is not just a color change you are asking for, it is also a lightness change. And it is a change from dark to light. Technically, that does change the playing field, significantly. With any type of digital image, because of the way that bits store tones, there are more bits used to store the light tones than the dark tones. This is why generally, making an image darker appears to be no problem, while making an image much lighter (trying to move details from shadows up into midtones and highlights) makes noise and banding much more visible, and correction much more difficult. Your request involves taking very dark tones and making them much lighter, so it can run into this type of quality degradation, which will be more visible with 8 bits/channel images, and even more if lossy compression was used. If someone did this starting from an 8 bits/channel JPEG, the lightened skin will probably look terrible up close.

One thing I ran into working with your file is noticing that the skin textures were different. If different ethnicities have different skin textures, and the only things that changed were the color and lightness, it might still look off because of the original texture.

If it included a face, then another factor is bone structure. If you change the color of skin to make someone appear to be a different ethnicity, but for example, the facial bone structure is not also changed to match that ethnicity, that too can sometimes make it look wrong.

If this is something you want to do a lot, then you might consider taking a class in fine art portrait painting. Portrait painters tend to be taught to observe and handle human color, tone, texture, and anatomy in more depth than us photographers and designers who just click buttons.

[PSKer]

You got me wrong. I didn't mean that. You made it very close to me to do it. But I haven't got the time yet to do like you did. And I appreciate highly appreciate that.

All I said is that my question wasn't how to change the color. It was rather why changing skin color is so difficult. That's all I said and all I meant. And I said that because someone misunderstood my reply to Dave who was so nice and polite and agreed that his articles were not about changing skin color.

[davescm]

Actually what I was pointing out was that those articles do give the technical information required to change skin colour. In describing how to correct colour, for various skin types, they describe the target to which the adjustments should be aimed. Those targets are equally valid whether correcting or changing skin type. From there it is a matter of using the existing tools and blending modes to adjust those parameters whilst leaving hue unchanged. Conrad is right in that when lightening the luminosity of skin in 8 bit images you can run into issues with the limited range of values used at the lower end of the luminosity scale. 16 bit should not be an issue in that respect.

It would be great to have a vectorscope in Photoshop, something which has been asked for for years.

Dave

[PSKer]

In general, I don't disagree with you or Conrad. Because of you I now have better understanding of color and insight into some tools to figure it out and manipulate it. And because of Conrad, my ability to change the color that I wanted to change has improved. But see the context of what was said.

After I improved in the skill and knowledge, and after you and I agreed on what those articles are about, someone came and claimed that they very directly and precisely answer my question.

IMHO, the discussion that followed was unnecessary.

But regardless, I was going to asked something anyway. Because I have been thinking if the hue is more or less the same, and I only need to change the luminance and saturation, then Curves and Saturation layers should do the job. I increased the luminance and reduced the saturation of the black arm in different percentages to no avail.

To what do you think this boils down? To the 8-bit thing?