How does color influence conversion to B&W?

Discussion in 'Black and White' started by Wasabi Bob, Oct 5, 2016.

  1. Wasabi Bob

    Wasabi Bob Mu-43 Top Veteran

    Like most people, my B&W photos are created from color photos; I use the Nik Silver Efex software. In the Sep 2016 issue of Shutter magazine, which is dedicated to B&W photography, I’ve been reading an article that tries to explain how certain color characteristics relate to the conversion to a B&W photo . Some of the info that is presented seems to suggest that it’s better to start with a slightly over exposed color image. I’d be very interested in hearing anyone’s comments on how this theory relates to your own work.
  2. Hypilein

    Hypilein Mu-43 Veteran

    Mar 18, 2015
    In my local jazz club there is a really ugly blue curtain behind the stage. When doing B&W conversions in lightroom (and most likely any other decent piece of software) you can access the luminance values for each colour. In the colour pictures this blue curtain is really annoying but it allows some amazing control of forground/background contrast because nothing else in the scene has this colour. Try using one of your images and moving the sliders for each colour to see what happens. When converting I often look at the colour image to see which colours stand out as being easily manipulated. I don't know what overexposing would do other than the general ETTR paradigma that gives you more leeway as long as you don't blow out the highlights at the same time.
    Last edited: Oct 5, 2016
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  3. agentlossing

    agentlossing Mu-43 Hall of Famer

    Jun 26, 2013
    Real Name:
    Andrew Lossing
    Colors don't affect B&W images if you just desaturate, but if you work with channels then of course it makes a difference... I think the overexposure is just making sure the maximal color values are captured by the sensor? Could be wrong on that last bit.
  4. fredlong

    fredlong Just this guy...

    Apr 18, 2011
    Massachusetts USA
    Real Name:
    If none of the channels are blown it's not overexposed. If any of them are it is and that's not so good.

    Pushing your exposure up gives you more latitude in adjusting the luminance level of the original colors when converting to b+w.

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  5. agentlossing

    agentlossing Mu-43 Hall of Famer

    Jun 26, 2013
    Real Name:
    Andrew Lossing
    Much better said than I!
  6. D7k1

    D7k1 Mu-43 Top Veteran

    Nov 18, 2013
    I like to work with HDR before I convert to B&W. I use PS & On1 normally to produce my B&W try to get my old darkroom tonal values.
  7. eteless

    eteless Mu-43 All-Pro

    Jun 20, 2014
    I wouldn't say that it's best to start with an overexposed image, however you need a reasonable amount of data to work with or you're going to get posterization (as changing the balance can often result in one channel clipping to zero). This image is purely to show that different ratios result in different effects, I don't believe that processing to black and white will magically make a boring lemon picture interesting.

    Colour image:

    Red channel discarded (Blue/green at 50%)

    Green channel discarded (Red/Blue at 50%)

    Blue channel discarded (Red/Green at 50%)

    The fire hydrant can be seen clipping to black when the red channel is removed as it has very few values from the other channels, this is easily seen with how little difference between the green and blue channel removals.
    There's also posterization in the lemon when the red or green channels are discarded (look at the darker area on the left) however there is none when blue is discarded, this is because yellow is a combination of red+green in additive colour.

    This final version is a heavy reduction in green, a smaller reduction in blue, and a boost in red. I used a mask on the green channel to reduce it's effect by around 30% on the lemon to avoid posterization while maintaining the reduction in background brightness.

    Increased exposure would have resulted in the red channel clipping for the post and lemon (it was already clipped on the specular highlights on the lemon) and would have actually resulted in less overall data.
    If the intent was always B+W biasing the exposure at capture using a blue filter would have resulted in more data to work with by lowering the red values a large amount, green a smaller amount, and not effecting blue (you can also look at it as boosting blue while maintaining the other channels). It's also commonly said that digital doesn't need filters, who am I to argue with the internet?
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  8. GBarrington

    GBarrington Mu-43 Veteran

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  9. David A

    David A Mu-43 All-Pro

    Sep 30, 2011
    Brisbane, Australia
    Interesting and informative post. Mike Johnston did a post in his blog The Online Photographer some years ago in which he showed a B&W conversion of a photo of a red apple on green grass. Both apple and grass had close to identical luminance values and were virtually indistinguishable in tone in the B&W conversion while strikingly distinguishable in the colour version. I spent some time after reading that post trying to find a scene where I had only red, green and blue elements of similar luminance value in order to render all 3 colours as virtually indistinguishable but failed to find a suitable scene.

    I've been re-reading Jeff Schewe's "The Digital Negative" and in it he describes a technique for seeing what the early stages of dealing with a RAW file look. like the steps the processing application has to take before it can display an image on screen for you to see. One of those stages is the creation of an image based solely on luminance values for each photosite on the sensor but with normalisation applied to compensate for the differences in strength of the red, green, and blue elements of the Bayer filter. I decided to try that technique in order to generate a black and white image which didn't contain or rely on any colour information, just luminance values. It was an interesting experience. The image had not had any gamma correction so it was very dark and I had to raise overall exposure and shadows and pull back highlights in order to get an image that looked like the way the scene looked when I took the photo. The controls in Lightroom looked very different when I imported the TIFF file—no white balance options, no red, green, blue channel options in curves, no hue/saturation/luminance options in the HSL panel. There was no way of making one part of the image darker or lighter for contrast purposes other than using global adjustments or applying an adjustment brush to a particular part of the image and effectively dodging or burning that part of the image. I had the same options I would have had if I had scanned a black and white print, imported the file and started to work on it. It was a very frustrating exercise and I think it may have cured me of my occasional urge to see what it would be like to photograph with a Leica Monocrom and only be able to work with luminance in my processing application and have to resort to the colour filters that black and white film photographers have to rely on for selective lightening or darkening of particular elements of a scene based on the colour of that element.

    Being able to work with individual colour channels in the conversion of a colour image to black and white is a great advantage, whether we choose to use those colour channels before or after the black and white conversion takes place.
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  10. Wasabi Bob

    Wasabi Bob Mu-43 Top Veteran

    Wow, thank so much for all the input. I definitely have a few theories to try. Basic desaturation usually comes out very "bla".
  11. bigboysdad

    bigboysdad Mu-43 All-Pro

    Aug 25, 2013
    Sydney/ London
    For anyone wanting a lazy unscientific way which involves colour to B&W conversion, here's a quick and simple practical (maybe cheat) method that can be used which often proves effective with SEP. Firstly open the colour image in Lightroom or Camera Raw, then switch to Greyscale mode and adjust positively or negatively (whatever suits), the saturation sliders consistent to the colours in the image. Then, after also applying your sharpening and highlights (highlights will often be reduced somewhat), switch back from Greyscale to colour again, then open the image in SEP. You can spend time making specific adjustments within SEP at this stage of course, but if you haven't got so much time on your hands, one of the 35 or so presets may well see you right. It will over 90% of the time result in a superior B&W image.
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  12. kinlau

    kinlau Mu-43 Top Veteran

    Feb 29, 2012
    As some have mentioned, over-exposing is really "Exposing To The Right" (ETTR). Digital sensors will capture more info if you slightly over-expose rather then under-expose. That info in turn, can be used to create smoother tones in B&W. But it really depends on what type of subject you're shooting. If you like high contrast, blowing out the highlights and crushing the blacks, it may not matter. OTOH, if you shoot a lot of sky, foilage, eggs or other subjects that give that smooth B&W look, then you'll likely benefit from over-exposing.
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  13. David A

    David A Mu-43 All-Pro

    Sep 30, 2011
    Brisbane, Australia
    Provided you don't clip highlights that you want to retain detail in.

    As has also been observed elsewhere, ETTR is really only a good idea at base ISO. At other ISO settings you reduce your dynamic range and how much you reduce your dynamic range depends on how much the ISO setting you use varies from the base setting. If you're trying to retain detail over the widest possible range while ensuring that your noise levels remain as low as possible given the sensor in the camera you're using, then you need to shoot at whatever that camera's base ISO setting is and ensure that you don't end up clipping any highlights you want detail in when you adjust your exposure.

    What I find is the best approach for me is to use the spot meter in spot highlight mode, lock my exposure based on a spot measurement of the brightest highlight area in which I want to retain detail, then recompose and shoot. In really wide range high contrast scenes, the exposure that technique gives you can sometimes actually be underexposure when compared to what the camera recommends if you did a normal meter reading which averages the whole of the sensor area but it can be amazing how much you can pull out of the shadows if you're careful. You can't pull anything out of a clipped highlight area, clipped highlights are simply gone forever and you will never recover detail from them.
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