How does 0 Saturation differ from Lightroom's B&W setting?

[CyJackX]

I've been toying around with it; some photos the results are nearly identical, but some have a pretty drastic difference. In one image a setting of 0 saturation retains a lot of detail in the hair, but with B&W, it becomes very soft and the hair all seems the same shade of gray.

I'm assuming this has something to do with RGB and the combination of the pixels to represent luminance, but I guess I wanted a concrete explanation, if possible.

[Mike Buckley]

Welcome to CiC!

I'm not familiar with the details of Lightroom and there may be no easy, short answer to your excellent question. So, I will rely on a quote from Vincent Versace's book, From Oz to Kansas: Almost every black and white conversion technique known to man.

He defines the term, chromatic grayscale, as "an image containing black, white, and a range of gray shades made up of colors that have equal values of R,G, and B. The best conversions of full color to monochromatic gray images are best done in the RGB color spaces. Even though the gamut of color in a monchromatic grayscale image can be easily reproduced in as small a color space as RGB, the file from which the grayscale image is being created is a full color one. Thus, it is important to preserve the full color integrity of the source image. [EDIT: Note that that is not done when you simply desaturate an image.] Also, the best continuous tone, monochromatic, grayscale digital photographic prints are made when all of the color heads of an inkjet printer are used and when the image has never left the RGB world."

He also adds that "if you simply remove all of the color from a color image by desaturating it...all you will see is an image in which different colors of equal luminance will all be the same gray...You lost 100% of the colors (other than gray) and 1% of image density, but the 1% that you lost contained the aesthetic qualities of the silver, black-and-white image that you were aiming to replicate. You also lost two-thirds of the file's data." (The use of the italic font to provide emphasis is mine.)

Having said that, every conversion technique has its place. Indeed, he explains the reasons (I won't bore you with) for trying the desaturation method to convert photos of clouds. Those reasons would surely apply to subjects that have similar characteristics as clouds. Perhaps the hair in your photo is a good example, but I would guess that using Lightroom's Multi-Channel mixer and working each channel value to your advantage might also solve your issue.

By the way, you might want to use the CiC Settings and Edit Profile menus to display at least your first real name and your general location on the left side of your posts.

[Manfred M]

I don't use Lightroom a lot, but the develop functionality is quite similar to Adobe Camera Raw.

The answer is that the desaturaration slider takes all colour out using a brute force method where the colour content of all channels is cranked down equally, whereas the B&W setting bias of different colours giving a more "natural" look. You will see this if you look at how the HSL tab works rather than the Basic tab.

Play with the HSL sliders and see how it affects your final image.

[Glenn NK]

Good post Mike.

And I think Manfred's suggestion to play with the HSL sliders is a good one.

Glenn

[nimitzbenedicto]

I don't use Lightroom a lot, but the develop functionality is quite similar to Adobe Camera Raw.

The answer is that the desaturaration slider takes all colour out using a brute force method where the colour content of all channels is cranked down equally, whereas the B&W setting bias of different colours giving a more "natural" look. You will see this if you look at how the HSL tab works rather than the Basic tab.

Play with the HSL sliders and see how it affects your final image.

Just saw Jack Davis on Creative Live dot com say the same thing about HSL.
( He was using ACR. But I think all he said can be done on LR5 too.)