Description of how to use the GIMP’s built-in tools to create black and white digital images.
Black and white digital photo processing-Part 1
It sounds simple: just take the color out of your image and you have done black and white digital photo processing.
Maybe it is the power of suggestion from current events, but this past year I have been fascinated by black and white photography. I’ve read many posts and watched many YouTube videos. Black and white photography has many, many varieties and nuances. It could be the study of a life time.
In this post I am going to talk a bit about what I learned, not as an expert, but as someone who might be able to make things more accessible.
As always, I have focused on how to use open source software. There are four software programs I have used: Raw Therapee, The Gnu Image Manipulation Program (a.k.a. the GIMP) and two plug-ins for the GIMP: G’mic and Nik Silver Effects (an older free version).
Shooting mode: imagination
One of my first takeaways: Digital photography is natively in color. To maximize the number of artistic options available to you, you are better off not using the monochrome options built into you camera. Except: If you use a camera that shoots, and is set to save, both jpg and raw files this isn’t a big problem, because the raw file (which is just the data from the sensors) will be in color. Because of this you have to use your imagination to take pictures you plan to convert.
In black and white you are relying on composition elements like layout (rule of thirds, golden spiral, etc.), leading lines, shapes, etc to draw the eye to the focus point you want. Often in black and white contrast takes the place of color to draw the eye. While in photography contrast is usually defined as the difference between light and dark, there can also be contrast between textures and shapes, and between areas that are in sharp and soft focus.
Another thing to keep in mind, is that some tools allow you to select which colors are dark and light, so contrast in color can be created, even if they are the same tone in the original. For example you can darken a sky to make clouds pop, or lighten (or darken) the color of a flower petal to make an insect more visible.
Converting to Black and White
The first method of turning a photo into black and white is “simple” de-saturation. Except that it isn’t that simple. For a digital image the color image has three monochromatic channels: red, green and blue. They are created by the demosaicing algorithm that translates the camera sensor data into an image. If you shoot in JPG then the camera does this, for raw files you need to use a demosaicing algorithm (I use Raw Therapee most of the time). These channels combine to create the color image. You can, if you wish, create a black and white by simply de-saturating one of the channels.
But wait…
Black and white digital photo processing isn’t actually that simple. The different channels tend to contain different types of information, as the example above shows. The article Perfect black and white with GIMP’s mono-mixer by Mora Photo describes this (worth reading even if you don’t use the GIMP, since most programs have a channel mixer and it describes the characteristics of each channel with examples). Because each channel has different characteristics, almost all de-saturation methods de-saturate all three channels, then recombine the channels. Different percentages for different effects. Most programs have a tool where you can specify the percentages for each channel.
The most simplistic de-saturation method is a combination of equal parts from each channel. More sophisticated methods try to create a sense of how your eye sees light and dark, for example, we tend to see a pure red as darker than a pure green. There are various formulas to account for that. Most are approximately 30% Red 60% Green and 10% Blue.
You can approximate the effect of different old school film types, by using different mixes of the de-saturated channels:
Film type | Red Percent | Green Percent | Blue Percent |
Agfa 200X | 18 | 41 | 41 |
Agfapan 25 | 25 | 39 | 36 |
Agfapan 100 | 21 | 40 | 39 |
Agfapan 400 | 20 | 41 | 39 |
Ilford Delta 100 | 21 | 42 | 37 |
Ilford Delta 400 | 22 | 42 | 36 |
Ilford Delta 400 Pro & 3200 | 31 | 36 | 33 |
Ilford FP4 | 28 | 41 | 31 |
Ilford HP5 | 23 | 37 | 40 |
Ilford Pan F | 33 | 36 | 31 |
Ilford SFX | 36 | 31 | 33 |
Ilford XP2 Super | 21 | 42 | 37 |
Kodak Tmax 100 | 24 | 37 | 39 |
Kodak Tmax 400 | 27 | 36 | 37 |
Kodak Tri-X | 25 | 35 | 40 |
The table above illustrates how complex a “simple” black and white photo can be.
How to find the channel mixer for each program:
Raw Therapee has a “channel mixer” method option in the Black and White tool under the colors tab. Raw Therapee also has tools to selectively change the brightness of individual colors.
The GIMP has a simple Mono-mixer: Colors>Desaturate>Mono-mixer.
The G’mic plug-in for the GIMP (and other programs) has a more sophisticated Black and white tool, in the that allows you to specify smoothness for each channel as well as specifying the percentage. From within the GIMP: Filters>Gmic, inside of G’mic: Black and white>Black and white. The upper portion of the tool has these controls.
For information about loading these open source (free) programs: Get going with the GIMP.
Black and white effects using different mixes:
Original color image. GIMP mono-mix of 33% from red, green and blue channels. Desaturated using the standard mix in G’mic: 0.3 Red + 0.59 Green + 0.11 Blue. Raw Therapee’s Black and white tool allows you to selectively change the brightness of individual colors.
Summary
When using a digital camera for black and white take the photo in color, not black and white mode to capture the greatest amount of information for each image. This allows you the most creative options when converting to black and white.
Because digital cameras capture images in the Red-Green-Blue (RGB) color space, the way to convert an image to black and white is to use a mix of the desaturated Red, Green and Blue channels. Every tool has some method of allowing you to specify the details of this mix. You can in some programs also isolate a particular hue to lighten or darken it for creative effects.
To be continued…
I plan to run through the black and white digital photo processing tools available in Raw Therapee and the GIMP in follow on articles.
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Post laying out the steps in a photo processing workflow that uses open source software instead of the more common paid subscription option.
Get going with the GIMP
The purpose of this is not to reinvent the wheel, there are thousands on YouTube about how to do these things, if you need more detail. This is just to give you enough information that you can quickly get going with the GIMP to be able to follow instructions in various how-to posts (like the ones to create a transparent fuzzy border or a twirled effect).
You can download the GIMP from www.gimp.org.
After download open the installer file and it will run an installation wizard.
If you shoot jpg files you can load them directly into the GIMP, and you are good to go. If you shoot RAW files then you need to do a bit more.
How to use RAW photo files with the GIMP
You need to use a RAW file converter before the GIMP can open the files.
The tasks that need to happen between RAW files out of the camera and the GIMP are de-mosaicking and applying lens adjustments. Most RAW converters have good tools to do exposure, detail and color adjustments as well.
There are several options, but I have experience with only two of them, RAW Therapee and DarkTable. Right now, I am preferring RAW Therapee, but I will sometimes try out both of them on a photo I really want to have turn out well. Because they have different de-mosaicking method options and use different algorithms for many processes so can result in a different look.
They are both easy to use, quite powerful, and can make photos look very good…even if you never open the GIMP at all.
They each work differently in how they interface with the GIMP.
This article by Davies Media explains about both programs and how to link them to GIMP: https://daviesmediadesign.com/project/open-raw-images-gimp-2-10/.
Once you have loaded one of these you are ready to get going with the GIMP using RAW files.
DarkTable
Darktable seems to have the most press right now, at least in searches and YouTube videos. It can be run as its own-self. In which case you load your photos into it, manage and edit them, changes are non-destructive and stored in a .xmp sidecar file. However, you cannot go directly from DarkTable into the GIMP as an external editor.
To get your files into the GIMP you have two choices:
- Save the file as a .tif, then open it with the GIMP.
- Add Darktable in as a GIMP plug-in. In which case you open the RAW file and GIMP opens DarkTable. You can make changes there, then when you close DarkTable, the adjusted file is opened in the GIMP, as a .tif file. The .tif file created when you open GIMPresides in the folder designated in DarkTable’s export dialog area. The default is a subfolder to the one containing the RAW files called “darktable_exported”.
I find both of these a bit awkward, because I have to load the folder, do whatever DAM (Digital Asset Management) tasks I want to do, then note the filename and location, close DarkTable, open the GIMP, locate the file I want to open, then the GIMP reopens DarkTable. If I already know the filename I can open it in GIMP directly. But Darktable will load only the one file and I can’t switch to a different one. That said DarkTable has some pretty awesome editing capabilities.
To download DarkTable: www.darktable.org.
RAW Therapee
If you install Raw Therapee for all users it will automatically add it as a GIMP plug in and put the correct information in the Raw Image Importer section in the Image import and export section of the preferences.
To download RAW Therapee: www.rawtherapee.com.
To add the GIMP as an external editor: go to Preferences and write in the path and filename to add it as an external editor. As shown in the screenshot below. The path in the screenshot is the default path when you load the GIMP, c:\Program Files\GIMP 2\bin\gimp-2.10.exe, so it will likely be the same for you.