My very simple B&W conversion technique

[rutt]

I used to be very high and mighty about B&W because I know how to make good color. But I've been taking a class at Harvard, Documentary Photography, and my professor just loves B&W. He lives in the world of Nachtwey, Davidson, &etc. So I've had to sharpen my B&W skills and rethink my ideas about what looks good in B&W vs color. I used to think that color was best unless there was a reason for B&W. Now I'm trying out the opposite approach: take to B&W unless there is a compelling reason for color. Once the course is over, I'll reevaluate.

Anyway, I've tried various B&W conversion techniques, including Gorman. Going to try Nik, but haven't gotten to it yet. But I'm liking a very simple technique:

1. Make 3 layers, stacked from top to bottom: "blue", "red", "green."
2. Copy the blue, red, and green channels into the eponymous layer.
3. Set the blending options for the layers: "blue" -> lighten, "red" -> darken, "green" -> normal
4. Try adjusting opacity first of the "blue" layer and then of the "red" layer. Often the "blue" layer doesn't help and the right opacity is 0. The same may be true of "red."

The justification: green is very often best for faces and faces are very often central to my images. But skies and water are often too light in the green and have better details in the red. Sometimes this leaves the blues too dark or loses contrast between blues and greens.

This doesn't give the look of any film or filter. I don't think there could be a film or filter that worked this way; darken and lighten layers aren't really analog things. But I could be wrong about this.

I've created an action set you can download here. This includes the action Rutt which sets up the basis for the above, as well as the Gorman action, and BD which implements my professor's basic idea. I'm going to give Nik a try, but haven't gotten there yet.

Feedback?

[divamum]

COOOL!! You are rapidly becoming my processing hero I have been significantly less-than-gruntled with my conversions, so any other methods are highly welcomed. Yay!

(PS "Gorman"... as in... Greg Gorman?)

[rutt]

Originally Posted by divamum

\
(PS "Gorman"... as in... Greg Gorman?)

The very same.

P.S. Unlike some of the other B&W conversion actions out there, mine only does the conversion and nothing else. No curves or sharpening or blurring &etc. So there is more work to do once it's over, usually curves and sharpening. Depending on your camera and light conditions, the red channel may yield very noisy skies. This poses a dilemma because the red channel also has the best skies (cloud contrast in particular.) Often a huge surface blur (radius > 20, threshold 2 or 3) will fix this without really hurting the clouds, but I'm still experimenting. These surface blurs take a very long time for large images at 16 bits, but are much faster at 8 bits.

[pathfinder]

I'll give your action a tryout, John..

PS I like this flag much better

[rutt]

Originally Posted by pathfinder

PS I like this flag much better

It was aimed at you. Do you think the whole image is stronger?

[pathfinder]

I think that is a complex question to answer.

I like this flag better, but the image suffers ( in my very humble opinion ) from the position allowed the shooter - too low and too far to the subjects right.

Again the cord intrudes. I would love to have seen her from farther to your right and higher, so that one could see more of the fire in her eyes, which I cannot see in this image.

I don't care for the edge of the bullhorn or whatever intruding on the flag at the upper border either - nit, and I might have cloned it out as an artist, but not as a pj.

The B&W conversion is excellent, but I take that as a given from you, John. I would expect nothing less. I mean that quite sincerely, I have learned a great deal from you.

As I said about the other flag, it is in the picture, so I feel it must be important to the image, or you would have left it out.

I do get her anger, that is for certain.

[jjbong]

Originally Posted by rutt

Feedback?

Nice technique. However, I think your justification of the technique recognizes that its utility will depend on the image. I took a number of shots recently in New Mexico at Tent Rocks National Monument. Lots of typical New Mexico dull reds and greens. For whatever reason, the detail in the rocks was invariably in the blue channel, with the red channel washed out everywhere but in the skies. I found that to get the best contrast, I had to do the following in every shot:

- Blend blue into red in darken mode, 100% (gets the detail in the rocks, and keeps the detail in the sky)
- Blend the new red into the green, darken or normal mode, some %

I tried your technique on one of these, and I didn't think the detail in the reddish rocks (which was what I was after) was as good. I can post, if you're interested.

[rutt]

Yes, I doubt that any one technique will work for everything, in the same way that no choice of file and filter can. This technique is good for a lot of things I like to shoot but certainly there will be cases when it is not. In fact, it is always possible to cook up an example which will defeat any technique and map all the colors into the very same gray. This just takes a little reverse engineering. [Afterthought: a technique might be "smart" and do some image analysis before deciding how to handle it. Then all bets are off. Are there any of these out there?]

I'm curious, though, it sounds like the green channel might be a pretty good start for these dull reds. The details in the green might come though pretty well in the red channel. Am I wrong?

[jjbong]

Here's a typical image:



Here are the channels from a section of the image:



You're right that the green channel isn't a bad place to start, but the blue is better, particularly in the highlights. There is a problem, though, if trees are important in the image (as in this one), as the blue tends to plug them. So I compromised on the blend, going into LAB and limiting the blend to where A is positive. For other images, trees weren't so important, so I could skip this.

So I replace the R with the B (darken mode) and use the resulting R to improve the G slightly. As you mentioned in your initial post, this is just the start - curves, shadow/highlight, some color boost round it out.

In my experience (not enormous), it's rare that the blue channel gives you what you want, but it does happen. And it happened consistently in this location (no surprise on the consistency).

[jjbong]

I've found Dan Margulis' channel blending algorithm in his Picture Postcard Workflow a great place to start, both in terms on learning channel blending as a technique and in approaching a particular image.

[Shishu]

I have been trying to use this technique more and more recently, but I have one question. Quite often, I do find that the green channel alone provides the best possible BW image, however when I use this method, and eliminate the blue and red layers (or simply by using Apply Image from the outset to apply the green channel to the composite), the resulting image is significantly darker than the original green channel alone. Can anyone explain to me why that is? Thanks!

[Shishu]

Here is an example.

Original:


Green Channel:


Rutt's method with only the green layer visible (equivalent to applying the green channel to the image):

[rutt]

This is a good question and I don't know the answer (yet.) I'll do some research and report if I can figure it out.

[Shishu]

Thanks! It's good to know I wasn't overlooking something simple, then.

[rutt]

I got help on Dan Margulis' mailing list. This is a color management issue, sort of a bug with photoshop's default configuration. It shows the composite image using whatever color profile it has. For me that would be sRGB. But it shows the channels with the default grayscale color profile. By default that's "Dot Gain 20" which has a gamma 1.74, so the two don't match. Use Edit->Color Settings and set the gray Working Space to Gray Gamma 2.2 and the issue is gone.

Note that this is only a problem with how the channels display. It has no impact on the final image.

[gmachen]

Originally Posted by rutt

..."Dot Gain 20" which has a gamma 1.74...

Hey Rutt, how does one calculate the conversion from dot gain to approximate gamma?

[Shishu]

Thanks Rutt...that did the trick.

Perhaps I didn't read Professional Photoshop close enough (that is probably a safe bet), but for anyone trying to use all 10 channels to the fullest, it seems to me that it is quite important to make this change, and should be explicitly mentioned somewhere.

[rutt]

Originally Posted by gmachen

Hey Rutt, how does one calculate the conversion from dot gain to approximate gamma?

I'm really out of my depth on this one. But if you Edit->Color Settings->Gray and select Custom Gamma from the pull down, you can see the gamma of the default grayscale color space. In my case it was 1.74 and I'll bet it's that way for must (Apple?) users. If you choose Gamma 2.2 instead, it will match the gamma of sRGB and you won't get the same shift when you look at the channels.

[rutt]

Originally Posted by Shishu

Thanks Rutt...that did the trick.

Perhaps I didn't read Professional Photoshop close enough (that is probably a safe bet), but for anyone trying to use all 10 channels to the fullest, it seems to me that it is quite important to make this change, and should be explicitly mentioned somewhere.

Yeah, I was wondering about the L channel vs however LAB is rendered. Does it have a gamma? It must. What about CMYK? Just thinking about that makes my head hurt.

The good news, though, is that in some important sense it doesn't really matter. Nothing changes except how photoshop displays the image...

[rutt]

I'd love to ignore this issue, but people just keep bringing it up. I say I don't know and B.D. tells me I'm an elitist because PS is so much more expensive than PS and it's so easy and all. I'm starting to feel like Martha Coakley.

So, how about it, LR fans, how to get a green channel conversion in LR/ACR? Forget the darkening, lightening with the other two channels for now. How about the most basic thing? I found the channel mixer but just turning green up all the way and the others down all the way doesn't get the expected result...

Please give me something to link the PJ folks to.