how to merge detail from one image and tonality from another?

[david_manning4]

I'm not very skilled with respect to digital PP, so please excuse me for asking a question that may have an

obvious answer.

 

I have a b&w photo that I am very pleased with, and want to make a large (at least 20"x30") print of it. I

converted it to b&w by using only the red channel; unfortunately, at least on my camera (20D), the red channel

has significantly more noise and significantly less resolution than red + green or red + green + blue, which I

expect will make a difference for the worse when it comes to large prints.

 

The tonality of the red channel b&w conversion is ideal; the resolution of conversions that involve the green

channel is ideal. Is there any simple way to merge two separate b&w conversions together, to get the tonality of

one and the resolution of the other? The difference in tonality between the two conversions is not actually that

large, but it is large enough to matter, and is large enough not to be reproducible in any simple way using Curves.

 

(If it matters, I'm working with the RAW file.)

 

Thanks for any advice.

[johnmarkpainter]

You could try to have each version on a layer and blend them that way.

Use the Red channel as background and then have the green one on top and blend in the opacity to taste.

You could erase (or partially erase) areas of the photo where you don't need the added detail.

[johnmarkpainter]

Oh yeah...also try setting the layers mode to "Multiply"

[geoff_foale]

Would using the Channel Mixer for B&W conversion be suitable here? Select Monochrome (name varies with some software) and try Green 60% Red 30% and Blue 10% as a suggested starting point. Vary the numbers as suitable, just make sure they add up to 100%.

[bernardwest]

I think the problem here is that in b&w, 'detail' is 'tonality'. In colour, detail can be distinguished by tone and/or colour, but in black and white, there is no colour. So, by changing the tonality of the final image, you will be changing the detail as well. I don't think you will be able to do this, other than using the red channel and running some noise reduction software over it.

[david_manning4]

John: I'll try to implement your advice (especially with respect to erasing the green channel to uncover the right tones in areas with little detail), thanks!

 

Geoff: Unfortunately the best tones are achieved by using Red 100%. :(

 

Bernie: Strictly speaking you're correct; perhaps I should have said that I want the macrocontrast (tonal distinctions between large areas of the photo) of the red channel, and microcontrast (tonal distinctions between tiny areas of the photo) of the green or red + green channels. That combination is at least possible.

 

Noise reduction is a good idea, but my bigger concern is resolution.

[bernardwest]

I can't think of how it can be done, but if you manage to work it out, let us know. It would definitely be a handy thing to be able to do.

[geoff_foale]

There is one other method which I find sometimes improves b&w tones. Add a Hue/Sat adjustment layer between the colour original and the converted b&w layer. Adjust the Hue setting until you get pleasing results.

 

Doesn't always work but sometimes this makes all the difference.