Today we’ll look at the 2nd of three B&W conversion techniques, grayscale.Tomorrow it will be luminosity.
Portland Head Light
Dark (well before sunrise) misty scene (the kind I love)
How is Grayscale computed?
- Grayscale attempts to take into account how our vision perceives color.
We do not perceive all colors as being equally bright
- Green is seen as being brighter than red which is brighter than blue.
In order to convert colors to match the colors the way that we see them (more or less)
- We can’t simply average all three colors equally as in the desaturation method
- We must weight each color proportionally to how our eyes see them
- The accepted weightings are:
- 30% of the red value
- 59% of the green value, and
- 11% of the blue value
- Not equal weights as in desaturation
The weighted average gives us the grayscale shown in example below.
- Often, it is hard to see a difference between luminance and grayscale
- This RGB test panel example shows that there is one – especially the green
Tomorrow – Luminosity
Yesterday provided an overview of three B&W conversion techniques. Each of them will be examined individually over the next three days. Today we’ll begin with desaturation.
NOT done by desaturation
A B&W conversion technique that you may want to avoid
- Because it has no redeeming features other than simplicity
- Some editing software offer it as a menu option under COLOR thus tempting users to use it.
- The resulting B&W conversions are rarely (like never) better than the alternatives
- This is best illustrated by yesterday’s overview example
Why would you ever use a B&W conversion that potentially could do this?
Especially when there are better alternatives??
How each desaturation is computed…
Are you surprised that a straight desaturation of the color image, as a means of B&W conversion, produced a uniform gray image? Once you know how desaturation is accomplished the mystery will be solved.
Desaturation B&W conversion is done by averaging the image’s RGB component values, pixel by pixel. The above image is pure RGB. This means that its color’s component R/G/B values from left to right are –
- Red = 255/0/0
- Green = 0/255/0
- Blue = 0/0/255
To determine each color’s gray conversion value, compute the average of each component’s strength –
- Red = (255+0+0)/3 = 85
- Green = (0+255+0)/3 = 85
- Blue = (0+0+255)/3 = 85
And, WOW, look at that! They’re all the same.They all convert to the same shade of gray. Maybe, just maybe – desaturation isn’t that great of a technique for B&W conversion (although at times you can get away with it; it depends on the image’s colors).
Now we know why the desaturation option gave the result that it did in our R/G/B image test panel.
Tomorrow – Grayscale
B&W photography, done properly, can be a true art form. I’ve written many posts on the subject. It’s time to take another look at some of them. We’ll cover all of the bases from basics to studying how the masters of the form did it.
Today – How to convert a color image to B&W (not all techniques are equal).
B&W Conversion Alternatives
What’s the difference?
There are numerous ways to convert a color image to B&W (not counting special programs and Photoshop plug-ins such my favorite, Silver Efex Pro 2). The first two that beginners encounter are –
- Desaturate the colors
- Convert the image to grayscale
A third technique, less well known, produces what I’ll call a “luminosity” B&W. It’s unfortunate that it isn’t well known because it produces the best B&W overall.
Of course there are other B&W conversion approaches but these three represent the basics.
Is one better than another? Can anyone tell the difference? Like most things – it depends. This post, and the next few, will illustrate the differences among them.
Let’s first consider the visual difference among the three. In each 2×2 illustration that follows, the arrangement of images is –
Can you see any difference among the three B&W conversions in this next illustration (Alexei Jawlensky – Self Portrait)? Not easy is it? The shading to the right of the face is probably the most noticeable. Otherwise, the differences aren’t that great. Ultimately it depends on the image’s colors & tones.
How about this next example? In this one the differences are obvious. The colors are Red/Green/Blue with values of 255/0/0, 0/255/0, and 0/0/255 respectively. (Please imagine that the right-most color is blue; it really was but there’s a color management issue using my screen capture program).
- Note the bottom right conversion, desaturation –
- What’s with that? I sure wouldn’t want that result.
- Check back tomorrow for more.
Another in my photo-a-day series. Same frame, a fence, but a very different subject from the past three subjects (barns) – today, a barn resident.
Darling (her name) & I formed a bond
A wide (12 mm) angle lens, 8 inches from Darling’s nose
Another example of an explicit frame; the fence serves little other purpose
Another in my photo-a-day series
Another barn framed by a fence; in this case the fence is more than just a frame
Same barn as two posts back; two years later; shot from opposite side
Framing your subject is an effective compositional technique. The frames can be explicit, as in this image, or more subtle as I’ll illustrate in later posts.
Been very busy getting the new home settled. Unpacking, contractors, new drivers license, car registration, voting registration, new electronics – and the list goes on and on and…..
Another barn with a fence frame
Having internet problems that are making blog posting difficult. For a quick post here’s an old favorite. I love using fences as frames.