Color space in B&W conversions

[bnnrcn]

What color space do I have to use in B&W conversions? Does it make any difference if I use either Adobe RGB or sRGB ? IMO the answer is no, because the image is in B&W and there are no colors other than tones of grey. But I'm asking in case my way of thinking might be wrong.

Thanks in advance for your help.

[Mike Buckley]

My suggestion is to use the same choices for color space as you use when post-processing color photos. That way your workflow remains consistent and, thus, tending to be error-free.

[Shadowman]

My suggestion is to use the same choices for color space as you use when post-processing color photos. That way your workflow remains consistent and, thus, tending to be error-free.

I agree with Mike regarding colorspace, perhaps you are thinking about color filters and color channels? I was doing a bit of experimentation with color filters (in NIK software) on an image I converted to black and white, using specific colors (green, red) tended to give the sky a infrared look, neutral filter didn't change the sky much and the blue filter tended to darken the sky. I chose to stick with the neutral filter. When converting to B & W using Elements, I will sometimes alter the RGB sliders but not always. Most post-processing tutorials I've read emphasize channel mixing with Photoshop which uses CMYK color model.

[bnnrcn]

Thanks for the info John. I have experienced the color filters in Nik and PS and the more I edit images the more I will see how they effect images. I was actually wondering if I have to switch from Adobe RGB to sRGB before saving the B&W image as JPG. This is what I always do with my color images but I couldn't see any point in doing so, because there are no colors other than the tones of grey in a B&W image. But as Mike mentioned, it might be a good idea to use the same choices as the ones used for color images in order to keep the workflow consistent.

I agree with Mike regarding colorspace, perhaps you are thinking about color filters and color channels? I was doing a bit of experimentation with color filters (in NIK software) on an image I converted to black and white, using specific colors (green, red) tended to give the sky a infrared look, neutral filter didn't change the sky much and the blue filter tended to darken the sky. I chose to stick with the neutral filter. When converting to B & W using Elements, I will sometimes alter the RGB sliders but not always. Most post-processing tutorials I've read emphasize channel mixing with Photoshop which uses CMYK color model.

[DanK]

I also agree with Mike. I use ProPhoto as my standard editing color space, and I see no reason to change it for B&W conversions.

[mknittle]

What color space do I have to use in B&W conversions? Does it make any difference if I use either Adobe RGB or sRGB ? IMO the answer is no, because the image is in B&W and there are no colors other than tones of grey. But I'm asking in case my way of thinking might be wrong.

Thanks in advance for your help.

The only time I have found that IT changes(automatically) is for the duotone/ quadtone treatment.in Photoshop CC. when you go to the image dropdown> mode>Grayscale It changes to 8bit/channel. Then it has to be changed back after the treatment.

[loosecanon]

For editing no need to change, but I always change the mode the greyscale before final sharpening and saving. This is especially important if you intend printing the image, as often printers will otherwise try to create the grey tomes by mixing colours - leading to colour shifts and using more expensive inks (and sometimes a loss of definition).
If preparing images for book printing it is very important to convert to greyscale - I know of one case where a printer printed the entire run as the K value of "colour" image - resulting in very light high key images!

[xpatUSA]

What color space do I have to use in B&W conversions? Does it make any difference if I use either Adobe RGB or sRGB ?

The conversion is done by your editor which applies a standard formula to each pixel to convert it from RGB to luminosity. That formula is different for each color space but your editor should know them and use them appropriately.

For example, sRGB uses this **: Y = 0.2126 R + 0.7152 G + 0.0722 B, and each RGB number in the pixel is replace by Y (luminosity, as can be seen in a histogram) - which is why it turns to gray, eh?

If you convert to an actual grayscale image (as already been mentioned) then those three equal RGB values per pixel are replaced by a single grayscale value and the file size is smaller.

I don't know the formulae for other color spaces but we don't have to anyhow.

** over-simplified for ease of understanding, actually the image has to be de-gamma'd, converted, then re-gamma'd.

In short, it makes no difference what color space you convert from to get gray-scale, i.e. "B&W".

[bnnrcn]

Thank you very much for your comments. You have been very helpful as always

[davidedric]

Hi Ted,

A supplementary question, since you obviously understand this stuff.

In Nik Silver Efex I can apply a colour filter to simulate the effect of a real colour filter when taking a b&w photo. Presumably this works on the underlying colour channels? In which case, would the colour space have some effect? I'm sure it's of little or no practical significance, just asking out of curiosity.

Dave

[xpatUSA]

Hi Ted,

A supplementary question, since you obviously understand this stuff.

In Nik Silver Efex I can apply a colour filter to simulate the effect of a real colour filter when taking a b&w photo. Presumably this works on the underlying colour channels?

Hi Dave,

Not familiar with Nik Silver Efex but, yes, any adjustment in any editor affects the image RGB values.

In which case, would the colour space have some effect? I'm sure it's of little or no practical significance, just asking out of curiosity.

Dave

Wow, that seemingly simple question is not that easy to answer, well not in a clear manner, anyway.

I'll try:

In Elements 6, if you run the color-picker around, it tells you RGB numbers from the working file. Converting the color profile on the fly does not change those numbers. Howver, in Elements 6, I think sRGB is the only choice of working color space.

On the other hand, in RawTherapee, the screen picker numbers show different between the various working color spaces available.

So, I'd say that the choice of working space affects the "underlying color channels", yes . . . BUT . . when you save your masterpiece, you have to save it as sRGB, or Adobe, or ProPhoto, or any other space you have available. If you save for the web (no embedded profile) the numbers should be adjusted to sRGB, I think. Then whatever opens the said masterpiece is supposed to see the embedded profile and adjust the colors so they look right on your monitor, your TV, your tablet, your smartphone, your laptop . . ya get the idea. If it doesn't see an embedded profile, it should display as sRGB.

Best I can do, sorry. Ask away if you need to . . .