Understanding color in B&W-photos

[aegirr]

I am trying to find detailed information about editing colors in black and white photography. I have googled many times and I have bought several book about B&W Photography, but I still have not have not found the details.

In order to make clear what kind of information I am after I am writing the following scenario:

I am editing an image in Lightroom Classic with the profile Lightroom Monochrome in Develop-module. I open B&W panel and I find 8 different colors: Red, Orange, Yellow, etc.

My problem/issue or lack of understanding is how do the different colors (8 colors) make the change to the image since the image is monochrome (one color) in the first place? I would like to learn more about this. I hope to get tips about this. Links and/or e-books. Or you can answer in the forum if the answer is not too long. Thank you.

[gary_sc]

Yeah, it seems confusing but it's really not once you get past the fact that the color in that image is still there but all of the colors have been desaturated.

What you need to do is go into the B&W Mix Panel and click on the little icon in the upper left corner. (See the arrow in the screenshot below)

Now go over to your image and mousedown on any given region and drag up and down. Notice that the color of the item that you clicked and dragged on is getting lighter/darker as you drag. This is becuase you're chaning the color of the image which in turn changes how it appears in the image. This is also a good example of why simply desaturating an image is not the best way to convert an image into a B&W image. 

Let me know if this now makes sense to you.

[aegirr]

Thank you for answering. I guess I "knew" about what you are telling me, because I have been using Lightroom for several years and almost all my photos (99%) are monochrome. I just love B&W. I guess my "problem" is almost an existential one: why B&W-photos actually have many different colors? Maybe the answer is: in order to get the different grades of gray. But "gray" is just one color so why do we then need several colors? Does this make any sence? I feel like I am on a journey to understand the core of B&W-photography but I am not there yet!  

[gary_sc]

Because sometimes you want different shades of gray to help separate items that would otherwise become invisible. Here's a quick example I created sometime back to help explain this:

Here's a color image:

Notice how the different colors make each object stand out. Now here's the same image but just desaturated:

Notice that it's really hard to distinguish that there are other colors here. The objects are not very distinctive.

But here is the same image that has been "fixed."

At first glance you probably cannot see much difference but please look at the relationship between the red, orange, blue, and green items and how they are more unique to each other in the last image than the 2nd image. One thing to focus on: note the bottom two items in the middle. In the desaturated image the blue appears lighter than the red yet, in the color image the red is a brighter color than the blue. Which image do you think displays a “truer color."

But what this all gets down to is that the final result is going to be YOUR vision of what the viewer sees. If you do not care to emphasize one color over another, fine. That's your prerogative. But just remember that the eye is always attracted to lighter objects and in a B&W image, you cannot use color to attract. 

Does this make more sense?

[D Fosse]

The raw file always contains color information by virtue of being a Bayer-encoded image. Each pixel in the sensor has a color filter in front of it, green, red or blue, so that's how the color is reconstructed in processing even though the raw file itself is a single channel.

If you choose a b&w profile that color information is discarded. Think of it as a funnel with valves for each color: so much of the red data, so much of the green data, etc, to make up the final mix.

This becomes much easier to understand if you have Photoshop: pull up a color image and look at each individual channel, R, G and B, by itself. That little exercise explains everything.

[richardplondon]

Perhaps a good way to think about this, is that these B&W panel tools are not changing "a black and white picture", they are changing HOW the colour picture information (that you started with) is to be now presented as a black and white preview.

Using the B&W panel sliders is very closely similar, to using the HSL Luminance sliders on an image that has been fully desaturated - e.g. by dragging all the HSL Saturation sliders temporarily all the way to the left. An image that still remains "officially" in colour mode and with all normal controls still active. So you still see (subtle or strong) changes in the B&W preview, as you alter the underlying colour presentation in whatever way. And bringing the Saturation sliders back up will show how you have changed that underlying colour presentation. 

I recommend giving those experiments a try, just to help develop accurate intuitions on how all this works.

[aegirr]

Thanks for all the answers. Very interesting!

I've got another question which is very theoretical: Is there a way to define/calculate a monochromo photo? In other words, is it possible to make sure, in theory, that an image is monochrome? I asked this in another forum and I got the answer that I should look at the histogram for the image and if I see any color in the histogram then the photo i color, otherwise it is monochrome. I checked this with several photos that I know are monochrome and in most cases the was no color in the histogram, but I found some exceptions.

How would you answer this question: Is there way to proof that å photo is monochrome and not color-photo (more then one color)?

[richardplondon]

Even if a photo within LrC is set to a B&W profile, or completely desaturated,or  has undergone a complete previous desaturation so that no hue information survives from the original photo, it is still possible some false colour may have been then added back in with split toning / colour grading or with Tone Curve. So those controls would need to be checked and zeroed as needed.

One way to be certain there is no colour whatever present, might be to export a version that is then reimported and a B&W profile assigned with no other adjustments made. Another may be to view in Photoshop and check there - you can set a monochrome working-space (or duotone, etc) for a particular document there, which you cannot do within Lightroom Classic or ACR. Those offer an RGB internal working space only. Another way I suppose may be to "print" to JPG out of LrC selecting an output profile which is monochrome-only (assuming such a profile can be sourced).

[Conrad C]

See if it helps to watch the video below. It directly addresses the relationship of color to black-and-white, how colors translate differently to black-and-white, and compares how various color-to-B&W conversion methods have different results and which one you might want to use. Blake is one of the more insightful teachers out there today.

The second half of the video demonstrates a powerful advanced Photoshop technique to consider if you want to take full advantage of the original image colors when editing a black-and-white version of the image.

[Todd Shaner]

A better understanding of how B&W film photography works may help.

https://digitalrev.com/2017/02/17/the-basics-of-shooting-with-black-and-white-film/

[aegirr]

Ok, I am getting this now. Thanks.

Just one more thing. Does a grayscale image have less color information then a monochrome image or the same?

[richardplondon]

An RGB image may be monochrome. This just means the result of the separate red, green and blue values of the pixels when combined, all happen to have the same hue properties, rather than varying in hue according to the original hues of the scene. That is not the same thing as being greyscale, since "monochrome" just means single-colour (hue) and that hue may be a neutral grey but does not have to be. This may be a tinted monochrome - sepia, cyanotype effect, whatever. In that case there is indeed more "information" present than there would be in a true greyscale image - in that you can tell what colour it has been tinted, as well as the tone values of all the pixels. 

A greyscale image has a format which is only capable of holding those tone values. It lacks all ability to portray hue, whether monochrome or polychrome. Photoshop can save out a greyscale JPG, for example, while Lightroom Classic cannot.