There must be as many ways of converting a RGB image to black and white as
there are photographers. There are entire web sites devoted to the many
ways of doing this. Many of these sources show us a technique to convert a
RGB image to black and white and then state 'move the sliders around until you
see something you like'. While is it correct that the final image is more
important than the original image, it always seemed to me these techniques
regulated digital black and white photography to the electronic equivalent of an
Easter egg hunt - we keep looking until we find something interesting. For
those who have never made their own black and white prints before, these
techniques can seem powerful. However, if you are the type of black and
white photographer who visualizes their final image and makes their own black
and white prints, these customary techniques may not offer the methodical
approach you are used to.
I find that I get to where I want to be much quicker and easier when I know
where I am starting from. So when I started researching how I wanted to
convert a color RGB image to a black and white RGB image, I looked for several
things. One, a consistent method that accurately converted the tones in
the color image to black and white tones as defined by the photographer.
Two, after the black and white conversion, I still had full control of tonality
by color. Three, the method was predictable and intuitive. Four, the
non-destructive. Five, and most important, the method fully supported
a visualization approach to creating a black and white image.
In my research, I never ran across a method that met all the criteria. So
I devised my own. I call it the Tone Management System, which is discussed
on the Tone Management
Choosing a method that creates accurate tones is more difficult than one
would seem. What is the definition of accurate tone in digital
photography? Is it %K, or percent black, as shown in the Adobe Photoshop
Info panel? Is it the value shown by the Curves control? Is it the
grayscale tones if the image were converted to a true grayscale image? Is
it the lightness channel of an image in the Lab color space? Each of these
will give different results when applied to the same image.
On this web site, I describe how to use the Tone Management System to create
accurate tone for each of the four definitions above. So, what we need to
do is decide what our definition of accurate tone is. Is it %K? Is
it the Curves value? Is it Grayscale tones? Or, is it the tones as
seen in the lightness channel of the Lab color space? Unfortunately, I
cannot give a step by step guide to help someone make that decision. My
personnel baseline for determining accurate tone conversion is the Photoshop
Curves control. If the Curves control shows that for a certain area of a
color RGB image the value is 75 and the Curves control shows that the value for
the same area in the black and white version of the RGB image is also 75, then I
consider the tone to be accurately converted. If you cannot decide which
definition of accurate tone meets your needs, I recommend you study all the Tone
Management System methods, view the examples, and then make a decision that
seems right for you.
Accurate tone is not about replicating exactly the tones
in the scene being photographed, unless that is what the photographer wants.
Accurate tone is the base digital luminance as chosen by the photographer.
Figure 1. Color Wheel
There are two basic ways of targeting color in Photoshop: color ranges and
color channels. A color range is a series of one or more colors that are
contiguously located on the color wheel. See Figure 1. An example of
a narrow color range is the reds. An example of a broader color range is
The Photoshop Select > Color Range command and the Hue/Saturation adjustment
allow us to select by color range.
color channel is the color and tonal information for one of the colors in a
color model. For example, the RGB color model has three color channels;
one for red, one for green and one for blue.
The Photoshop Levels and Curves adjustments allow us to select a specific
color channel and make adjustments just for that color channel.
As we will see later, we can use the combination of the Select > Color Range
command and Levels/Curves to allow us to make adjustments to color ranges
using Levels and Curves.
Being able to select by color range or color channel gives us another option
to target areas of our image to modify their tone. It is this level of
control that I wish to maintain in my black and white photography.
Without going into Statistical Process Control, Six Sigma or other process
improvement methodologies, there is one thing they all have in common. If
we cannot reasonably predict what is happening in the method or process we are
using, then we really do not have control. So, regardless of the black and
white conversion method, if someone just moves sliders around until they see
something they like without knowing ahead of time what is going to happen when
they move the slider, then their black and white method is more akin to opening
presents at Christmas; they don't know what they are going to get, they just
hope it is going to be something they like. Predictability and control go
hand in hand. I want a technique that I can use in a predictive and
controllable manner when working on an image.
Simply put, a method that is intuitive is a method that makes sense to the
user. It is true that intuitiveness varies by person. And it should
also vary for a person as they gain experience. For example, using the
Curves control to a new Photoshop user is probably not very intuitive. But
with experience, one would hope that the Curves control will become intuitive.
I will also admit that managing tone by color in a black and white image may not
seem intuitive. However, experienced black and white photographers have
used color filters to darken a blue sky or green foliage for decades.
Non-destructive methods are any computer based image editing technique that
changes an image's appearance without permanently altering the image's pixels.
They allow us to 'undo' a change even years after the change has been made.
Simply stated, visualization is the art of seeing the final image in one's
mind and then using traditional and digital photographic techniques to create
it. I do not want to settle for what Photoshop automatically gives me.
I want to use Photoshop, or any other image editing software, to create the
image of my choosing.