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Below is a photo taken by me:
Below is a photo I found on internet:
There are some visible differences between the two. One is dull and the other has visible blacks and whites.
I feel I need to study the meaning of some technicalities for BW conversion.
I can't make out what I have done wrong?
What the differences between in BW conversion of these two photos?
What technical terms or rules of thumb do I need to understand for a black and white conversion of a photo?
To convert to black and white, the first thing you need to understand is...
Take a look at this post: Which color filter do I use for a black & white portrait?
It shows that there are several places to grab the grayscale information.
Back in the days, when you used b/w film some of these decisions were made before exposing the film. For example, to get more interesting sky you used a red filter.
A specific topic about color>gray is to understand complementary colors.
If you want smoother skin tone, you use some conversion based on the red channel. The skin has a reddish tone. If you want more contrasted and darker skin, use a complementary one. Green, blue or a combination of both.
The same applies to landscapes, sky, water, architecture.
What is one of the most important technical concept? RAW
Understand among other things this: What's the point of capturing 14 bit images and editing on 8 bit monitors?
the other has visible blacks and whites.
Who says that your photo does not have visible black and whites?
Here are they:
Your histogram clearly says your photo has them. The point is where are those related to the other.
The problem is that you already made decisions on the conversion so I am totally limited by it.
You do not have one photo here... you have two. At least in terms of illumination.
We could try to fix this using curves, but the result is bad because we do not have enough information... (not in raw, not in RGB channels)
Notice how I tried to fix this using a two-stage curve. The kid, has more contrast, making the kid less dull.
But we need to think in terms of:
I am not doing exactly dodge and burn because I am lazy. But I am masking the two different photos on your photo, adjusting curves for the kid. (the first part of my previous curve)
And merging them together, with the other part untouched.
Adding some vignetting perhaps?
Of course, we could tweak this better. The trees, the sky, the mother, the other kid.
Monitor calibration, color profile, noise, light zones, clipping, dynamic range.
P.S.
We need to talk about composition, but that is another issue.
Grayscale can be sort of a Do It Yourself activity. The issue is, just how dark or bright should some shade of red or green appear in grayscale? The standard Grayscale Menu converts it the way the human eye perceives brightness of colors. The Grayscale menu is from the way television cameras did it in the B&W days. It is how B&W film does it, matching the eyes response. That is the standard solution, considered "correct".
But there are other ways too, like the Channel Mixer menu, where we can specify how the various colors should be rendered in grayscale. Technically that is NOT a grayscale conversion, but instead is an editing operation, subject to whim, any way we want it to be. The difference might be considered pleasing instead of accurate.
My guess is it is the top portrait that you perceive to be dull and lacking contrast, and that the bottom architecture is full contrast with "visible blacks and whites". But if you look at those two histograms, clearly the top portrait has already been edited to seriously clip both ends, which is blacker blacks and whiter whites (the sky is white, the shadows are black). IMO, a bit more White Point, down to 230 where the data actually starts, might help it. Anyway, a little clipping could be called standard practice in many cases of grayscale.
The architecture image was not clipped, but that subject itself has more contrast, but it is NOT blacker blacks and whiter whites. Just more of it is nearly black or nearly white. Large black areas can be dramatic, esp if contrasted with solid white.
Ansel Adams modified his classic photos with drastic darkroom procedures (would compare to drastic editing in digital), and one of his basics was that grayscale seriously needs ample contrast (blacker blacks and whiter whites, and having some of both was his requirement), and he did this in ample degree, perhaps to a fault in some cases. Because Grayscale has no color to help it. But in color images, the color itself is often the contrast, and often serious clipping is detrimental to color (it changes the colors), where it can be helpful in grayscale.
See my site at https://www.scantips.com/lights/graycard.html#ansel about easy and standard methods using the Adobe Levels control to increase the contrast of grayscale images (without altering the tonal differences of colors). It is done "by eye", judging the preview. My own notion is that most Grayscale images need some degree of this contrast enhancement. Try it, you'll like it.
Light is everything. And then, the darkroom. If you are doing black&white on film, you'll likely converge to "Multigrade" paper where you can select the contrast by using one of different filters. And if your scene needs different amounts of contrast/exposure for different parts, you use dodge&burn techniques for giving them those.
Of course, a digital darkroom can do most of those (and more) by combining several tools, but if you have the opportunity to spend an afternoon or so in an "analog" darkroom, this can be quite enlightening.
And, of course, people have been conditioned for centuries on the results of those techniques with regard to black&white photography, so you are not working in a cultural vacuum. Look what digital sound production has given us: one can do everything, and the majority of what is done digitally is based on reproduction of samplings of acoustic instruments.
And of course, photographers had been conditioned to visualize all their work in terms of light and dark. Their viewfinders gave them color, and they had to know and plan what the photographs would look like. And their flashes meant business.
Color leaves a whole lot less leeway to mess around with: one of the most important aspects of color photography is white balance. You could say that one of the cornerstones of black&white photography is white imbalance: sculpting contrasts that the original may not actual contain to a similar degree, and that process starts with the composition. You avoid shadows in color photography. You work with them in black&white photography. So you really cannot start thinking about black&white in post production: you have to work for it composing your picture.
Your picture contins the full range of levels from black to white, but the only thing that is fully white is the sky, which is uninteresting. The important content of the picture is compressed into a narrow band of levels.
Use the Levels function of a photo editor to allocate the full range to the important content. No matter if the bright sky goes 'off the scale'.
There are more subtle techniques (curves, etc.) available in the better editors. But, in this case, the sky is washed out already, and I'm happy to lose the trees.
(Maybe, ideally, shoot a picture where this doesn't have to be done.)
