Case Study: Conversions to Black & White

One of the early "limtations" of dSLR photography was that no longer could you change from colour to black and white film. To produce a B&W shot you had to use some form of processing conversion in your own digital darkroom. Newer dSLR cameras now often have a menu option to record only in B&W, but this uses fixed algorithms and may not result in what you hope for. This "Case Study" looks at various conversion options that start from a colour original.

Case Study: Converting a Colour Photo to B&W



- An introduction to various basic approaches -



by Micholand







Black and white still hasn't lost it's fascination even in nowadays more and more digitally world. In fact, a black and white version can improve an already good colour image even more -- simply because a black and white version of an image lays the focus more on graphical content, like shape and texture, and therefore colourful objects don't detract from the main motive. Or, in other words, converting from colour to black and white can lead to a totally new assessment of a photo.



If you use a digital camera which has a b&w mode, you get a digital black and white photo straight out of the camera - a very comfortable and easy way, but with limited user control in the end, because the camera uses some predefined internal settings. We disregard here the use of colour filters in front of the lens, which is common in (analogue) black and white photography. However if you shoot in colour mode, you can have both a colour and a black and white image!



In the world wide web one can find a lot of descriptions how to exactly convert an image from colour to black and white, often in a step by step tutorial for specific photo editors, and each method has its supporters or are said to be the best. As always that's totally biased and the bottom line is that there are a dozen ways of doing it and most of them work reasonably well.

In the end the method that works best for you simply depends on your personal workflow, the time you'll like to spend editing and also the tools you're used to or have available.



So this short article just gives an introduction into some basic approaches to convert a colour into a black and white image by digital post-processing. Of course there are many more variations possible in the end, but mostly all do have the shown basic techniques as a baseline. And as there are also a lot of different softwares available for the digital darkroom work nowadays, the shown content below is not supposed to be a step-by-step guideline for one specific photo editor. In fact, it's only a general overview and therefore your available software tool for editing may not offer all the mentioned possibilities. But in the end you should have got a rough idea and overview about the basic techniques to convert a colour image into a black and white image.







Well, here's the example colour photo we want to convert into a digital black and white using different techniques:





Original photo in colour:









Let's start!



Maybe one general hint at the beginning: Always backup your original shot and work with a copy! During the conversion colour information will be lost irrecoverably and the original can be quickly overwritten by accident!







Technique #1 – Convert to Greyscale



In every digital photo editing application you'll find the simple mode "Greyscale". With this command a colour image is changed from one of the colour modes to the greyscale mode by using internally predefined conversion tables, which normally weight the values of each colour channel in a way that retains the apparent brightness of the overall image.



This is a simple and straight forward method, unfortunately sometimes this conversion produces a black and white image which is a bit looking too greyish.





Convert to Greyscale, the result:









Hint: Switching to greyscale mode is always the final step one should do in all the following described approaches to really get a greyscale image and not to waste space by saving a picture in a colour mode without having any kind of colour information in it!







Technique #2 – Desaturation



Another option to get rid of the colour is the function that is normally used to increase or decrease the colour saturation/hue.



If a colour image is desaturated completely - by moving the saturation slider all the way to the left to -100% - all information of colour is "removed" and it's becoming grey. From technical point of view the image is still in colour mode, but only looks greyish because every pixel has exactly the same amount of red, green and blue information and these do - so to say - remove each other and let the colours therefore disappear.



Converting the picture after this desaturation to greyscales will give slightly different results to a direct conversion ("Technique #1") due to the fact that colours, which saturation have been reduced, will be rendered brighter.





Here's the result after use of Hue/Saturation to desaturate [colour saturation set to -100%] completely:











Technique #3 – Black and White using Channel Selection



A normal colour picture is a combination of three greyscale channels. Now a simple way of converting to a black and white image is to select one of these channels and discard the others.

This procedure is however not available in all photo editing applications!



The normal monitor view shows all three colour channels of the image on top of each other. Some programs now allow to split this image into the individual tones, either by generating three new images or having a channel palette including them there. However, when looking at each channel the image may possibly be displayed in a single colour, perhaps red tonality with different brightness or already in levels of grey, depending on the actual program's settings. Choose the default settings to be greyscales. Now you can use the channel that pleases you best and afterwards convert to greyscale.





3.1 – Custom greyscale by using RGB mode



Before directly switching the picture to the greyscale mode, be sure to look at the individual colour channels to see how each channel might look on its own. In particular the red and green channels, the blue channel frequently contains substandard detail only. If one channel is pleasing, convert to greyscale while viewing this single colour channel. All brightness values in that channel only are retained and the data in the other channels are abandoned.





B&W results for the individual three channels:







Red Channel:







Green Channel:







Blue Channel:








3.2 – Custom greyscale by using CMYK mode



This mode is mainly used in process-colour printing and consists of the following four colours Cyan, Magenta, Yellow and Key (Black). If all of them are used together they give printed a dark, covered black.



After a CMYK mode conversion of the image there are again four new channels, each containing slightly different greyscales than in the RGB mode.

Now exactly the same method as explained in the previous section "3.1 – RGB mode" can be used here, too:

Select only one single channel of those four channels containing the print colours Cyan, Magenta, Yellow and Key/Black and afterwards convert to greyscale.





B&W results for Cyan Channel | Magenta Channel | Yellow Channel | Key/Black Channel:









3.3 – LAB Colour and use of Lightness Channel



Another colour mode which can be used for black and white conversion is LAB colour. It is composed of three channels, the lightness channel, with most of the tonal values of the image in it, and two colour channels, “a” which contains red/green information and “b” containing blue/yellow info.



So the approach is to make a conversion of the image into the LAB mode and just use the brightness information. After selecting the lightness channel only, the image is converted to greyscale and the other two channels are discarded again.





Use of Lightness Channel:











Technique #4 – Custom greyscale by using Channel Mixer



The most powerful technique is the use of the channel mixer, as it allows the user to control how much each of the colour channels contribute to the final greyscale brightness.



In b&w photography often colour filters are used in front of the lens to only let pass light with the wavelength of the same colour and block the others - similar to how colour filters are used for each pixel in a digital camera's bayer array. With a yellow filter for example, the yellow tones are becoming white and all the other colours are shaded. The effect of colour filters is always restricted to a specific wavelength of light and independent of the motive and they are named after the hue of the colour which they pass, not the colour they block. In general one can increase contrast in a given region by choosing a filter colour which is complimentary to that region's colour.

Though, with the channel mixer you can choose, from an unlimited amount of filters, the one which suits the motive the best and decide which colour will produce the brightest or darkest tones. You only have to check the option monochrome/greyscale in the channel mixer dialogue box for black and white conversion, better to say to get a greyscale view of the image.

If one channel is set to 100%, e.g. red, and the others to 0%, then this channel is extracted solely, which is the same as selecting only the red channel in the colour channel view/selection.



Channel mixer can be used either in RGB mode or CMYK mode; both colour modes deliver slightly different results, though.





Channel Mixer - Red 70% | Green 18% | Blue 12%:









Channel Mixer used in CMYK mode - Cyan 58% | Magenta 32% | Yellow 10% | Key/Black 25%











Other Techniques:



- RAW converter:

Directly do a black and white conversion in the RAW converter itself, by desaturation, fine-tuning of the white balance based on the desired black and white look and all the other sliders available there.



- Third party plug-ins:

Use a third party plug-in, which has been designed specifically to convert colour images into black and white images. There are plenty of them available on the web.







Other considerations:



The best results are achieved when there is no colour cast in the image, so take care that the image has the correct white balance.

Also you need to be pretty careful with the exposure, especially be careful not to overexpose, otherwise you'll lose the highlights. In fact, blown highlights are less distracting in colour photography, since the colour adds another dimension to the picture. On the other hand black and white lives and dies on tonality and blown-out highlights are much nastier.

And of course after the black and white conversion there are a lot of further enhancements possible with the image. Levels and curves can be used to provide further control over tonality and contrast, selective areas can be dodged and/or burned and a toning, e.g. sepia look, can be applied, et cetera.





Want to get more insights or learn a how a specific workflow is done exactly, step by step, in your used photo editor? Then I recommend to have a look into one of the plenty available photo editing books and/or do a search in the web





I hope this little article helps to understand a bit better the basic digital approaches. Nevertheless, it's only a brief overview of converting a colour photo to black and white. Of course no one is perfect, therefore if I've forgotten anything just post.



Last but not least I'd like to thank all members of Dyxum who share their knowledge for free, this is of great help, a nice inspiration and further education.





Thanks for reading!

Michael

This is our second “Case Study”. We hope to run more in order to help people develop either photographic skills or processing techniques. Please note that questions and discussion are welcomed.

Edited by Micholand - 24 September 2017 at 11:20

Thank you Micholand, a great article that will help to enhance my skills.

Now look at this, I was just playing around with b&w,not happy with the result and searching for posts about this on my favorite forum about converting to b&w and bam!

Micholand, you made my day :)

I've been searching for something this for a while. Thank you very much for investing the time to share!

I'm glad you all found my article useful
To be honest, at first I was a bit surprised about the lack of responses after it was rolled out, but with such nice feedback now I think it was worth the effort. Anyway, looking forward to see some of your b&w attempts in the Dyxum Photographs.

Frankman wrote: I've played a bit with B&W conversions, but I can never tell when I've got the ratio of channels right when using the channel mixer technique. I guess it's all trial and error and developing "the eye".

You definitely need some kind of "b&w view/eye" for this, so try to think in terms of colour filters, which detail should be bright or dark and then adjust the corresponding or complementary colour out of the wheel of colour.
As a general starting point analyze the individual channels first, choose which channels offer you the most detail and tonality on an image by image basis. Select the channel with the most detail to be the dominant channel for the channel mixer and then adjust the sliders to add/subtract some of the other colour channels. The choices made are purely aesthetic. In order to maintain the density or overall brightness of the image, the percentage totals should not exceed 100% otherwise there is a risk of losing highlight information. Play! There are many interpretations possible, in the end it's always a personal thing, everyone to his taste

Edited by Micholand - 27 April 2008 at 20:06

Dirk wrote: Thank you Micholand, a great article that will help to enhance my skills.

And to 2nd Polossatik, sorry Bob, thanks a lot for the examples.

I also find this incredibly useful. It lost me first time around, but when I want back and put a little effort in, it all made sense. Thanks, Michael, for sharing. And the examples from Bob J are icing on the cake.