Need to wipe out a color stain

[BrianF]

So I've been trying to use the HPE tools to do something that feels like it ought to be straightforward, that is, to wipe out a blue ink stain on an old black and white negative. I've been trying some techniques I saw that required the full version of Photoshop and the use of Channels, so I tried to duplicate the technique using the Hidden Power tools and doing an RGB separation. However, somehow the technique has no effect this way. Seems like there ought to be a simple way, as the stain is blue and the rest of the image is black and white, but I'm just not finding it.
Does anyone have any ideas?
(I'm suspecting that what I need to do is the equivalent of adding a Channel Mixer adjustment level in PS - is there a way to do that?)

[Richard_Lynch]

I don't think channel mixer will necessarily be the way to go, though it is a potential solution (depending on the color of the blue). I would really need to see the image. But think this way: if the blue is pure (doesn't bleed into the green), then you could potentially separate RGB and use the green channel which generally reflects what we see as black-and-white.

if that is not the perfect solution, you may be left to making a selection of the area and trying to do an adjustment with curves or other layer calculation. if I could see the image, I could give you a better idea.

[BrianF]

Well, it isn't pure blue no, some of the damage shows up in the green channel. What I've been trying is to take advantage of the fact that it's a color stain on a bw image and scan it as a color positive (lets me see that the blue is blue).
Last night I tried doing a luminosity separation, and as I suspected, the color layer showed only gray and the blue stain. I wonder if the right appproach is to somehow fix the luminosity value of everything that shows up blue in the color separation layer. I don't know how to do that, but it feels like a clean way to get only the damaged area selected. It seems like I'm very close, but not close enough.

[Richard_Lynch]

The problem there is that you don't have an even stain. You can custom select all you want and I don't think you will make quick work of it. I am wondering why you aren't interested in just cropping the image down?

In any case, I took a poke at it quickly. I tried not removing the stain, but duplicating it by dying the whole film. It didn't work wonders, but it worked in spots close to the subjects. Then I sharpened, etc. I think you'll see a decent result. But I think it can be cropped still tighter. It may not be what you want to fix, or how you want to fix it, but won't it make for a better photo?

I'm trying to upload with layers so you can see what I did, but I might have to flatten. yep...

[Racc Iria]

Hi, Brian.

I took a quick stab at it. Here's what I did...
Took the image you posted above and inverted it. Then I copy and pasted each color channel back in as a normal layer. The blue channel was the cleanest, so I put that on the bottom and used it as the base.

I added a layer mask to the red and green layers and painted them in using the best of each, essentially masking out the stain.

Then I added a levels adjustment layer and adjust it so it looked good. Then I added a second levels adjustment layer and painted in the mask to even out the curtains.

It's not quite perfect, but the stain is essentially gone. I did not do any cloning or healing.

[BrianF]

The problem with cropping is that while in this one case I could crop out the stain, I have at least four other negatives with blue stains on them, and those have them over the subject in some cases. That's why I was trying to find a general way to tear out the stain. I was encouraged that using the Hidden Power tool to separate luminosity from color gave me a color layer that had only the stain, so I was thinking that I could use that to create a layer mask to adjust the luminosity layer. I guess that's harder than I thought.
Are you saying that what you did was to make the whole negative image the color of the stain, to equalize things?

Racc, what did you do exactly with the layers masks? I understood what you were saying about just painting in the parts of the red and green channels that didn't show damage, but not what exactly you did with the layers masks.

Thanks a lot for the help, everyone, I really appreciate it.

[Gary Richardson]

Had a quick go with your image.

Converted to positive.

Switched to Blue Channel, converted to Greyscale, discarded other channels, then converted back to RGB. Saved As "Blue Layer".

Back to original, Switched to Green Channel, converted to Greyscale, discarded other channels, converted back to RGB, then Saved As "Green Layer"

Opened Blue Layer image, and Green Layer image. Copied Blue layer and pasted over Green Layer, set blend mode to Darken. This got rid of most of stained area.

Created new layer, filled with 50% grey, set blend to Soft Light, and evened out irregularities in tone using soft black/white brushes at 5% opacity.

Curves layer to adjust contrast and brightness.

Colour blend layer to add back the slight blue tone that original image had.

Bit of a rush attempt, take a little more time and you should get better results.

[Racc Iria]

Hi, Brian.

In a way I kinda did what Gary did, except I just did all the copying and pasting within the one image and used layer masks for more manual control. Again, I just took the RGB color channels and pasted each of them onto a normal layer. I will also point out that this only worked because the image was intended to be grayscale.

Anyway, I noticed that the stain was nearly gone in the blue layer, so I used that as my background layer. However, the people seemed to have more details in the green layer, so I added a layer mask to the green layer (originally set to hide all) and painted with white to reveal the green layer only over the people and part of the curtains.

At that point the picture looked okay, but there was still some problems with the upper curtain area where the stain was. I noticed that in some of those areas the curtains in the red layer looked better, so I added a layer mask to the red layer set to hide all and painted with a soft white brush to reveal the curtains and parts of the wall that looked better.

Then I added a levels adjustment layer and just dragged the white and dark points to match the histogram. I noticed that the very top of the curtains were too light and didn't seem to match, so I added a second levels adjustment layer and darkened it up to match the rest of the curtains, but since that made the rest of the image too dark, I filled the mask with black (hiding everything) and then painted with a soft white brush to blend back in the tops of the curtains until they matched the rest of the image.

Again, I did all of that pretty quickly, so it wasn't a perfect job. More time spent on it would probably yield better results. The nice thing about using the layer masks is that it allows you to manually and selectively blend the different layers together. In this case, using the best of each color channels information to create one good grayscale layer.

[Richard_Lynch]

Originally Posted by BrianF

Are you saying that what you did was to make the whole negative image the color of the stain, to equalize things?

That was my choice. You will note that there is some tonal difference when you do this, and essentially you will be left to clone out some stuff. If it were an even stain, you might have more luck with some other type of adjustment, but the fact that it is uneven in tone and density pretty much leaves you to do some manual pickup. I'm all for using calculations and clever devices, but this is not a situation where you will calculate out the difference.

[BrianF]

Richard, yes, I see what you mean now, even after I created a layer mask based on the color separation, there was no way to magically make things even out, due to the unevenness of the stain that you mention.
I'm going to try fixing up the other images now, armed with all the tips you guys have given me. Thx!

[Richard_Lynch]

All that said: While it can be tricky, using dodge/burn with a selection can help you edge some of the tone back to fitting with the rest of the image. You may have the best luck with rebuilding (clone, patch etc.).