Everything Corey says in his answer is true.
On the other hand, though, digital also has a few advantages. There's one in particular that's a BIG one with regards to B&W photography:
In terms of black and white, do color digital images lose information
in the conversion that film would retain?
With digital we can apply different colored filters to the same shot after the fact.
This derives from the most obvious advantage of using Bayer masked digital cameras instead of B&W film: color information is preserved.
Even if the final output is intended to be monochrome, this allows for changing color temperature and white balance after the fact to alter the tones (brightness levels along the grey scale between full black and full white) of differently colored objects after the fact. The adjustment of the ratio of tonal values of objects of different colors can be even more pronounced when using color filters.
When shooting B&W film, the tonal relationships between objects of different color are locked in as soon as the negative is exposed. Any filtering to make similarly bright objects of one color a brighter shade of grey than equally bright objects of another color must be done at the time of exposure. The monochrome negative only records a shade of grey. It can no longer differentiate between objects that were different colors.
If we use a red filter when we shoot film, we can't go back based only on the information contained in the negative and make it look like we used a green filter, or even an orange filter after the fact. With a digital raw file from a Bayer masked sensor, the possibilities of adjusting relative tonal values based on the colors of objects in the scene are near endless!
Here's an image I shot a couple of weeks ago at an outdoor music festival with a color digital camera. In post I applied a green filter as well as used the color temperature, white balance correction, contrast, shadow, and highlight sliders to set differences in brightness based on color and reduce the influence of the "fog" on stage.
EOS 7D Mark II + EF 70-200mm f/2.8 L IS II, ISO 3200, f/2.8, 1/500 second.
Here's the same image with a red filter applied. All other processing settings are exactly the same.
From the significant increase in brightness, we can see that the light in the scene at the time was mostly red. Using a green filter under mostly red lighting has the effect of local contrast enhancement as well as decreasing brightness.
Yet even adjusting for brightness by reducing exposure 1.67 stops, we still see differences in contrast between some objects and others.
The bright parts are brighter, the dark parts are darker. Compare the detail in the wrinkles on the t-shirt (which was actually black). Look particularly at how the the multicolored guitar strap is rendered in each example. Also, notice the tuner assembly on the out of focus guitar tuning head low in the foreground. Look at the differences in the beard and the hair on the arm. The effect of the fog reflecting the red light is still there. Try getting the first image above with ASA 3200 film and a green filter in front of the lens. You might could get close, but it would be very grainy. Or even worse, try getting the first result above that used the green filter with a film negative in the darkroom if a red filter was in front of the lens when it was shot. You can't.
Just for demonstrative purposes, here's the image in color with the CT/WB/HSL settings used to create the above monochrome images and exposure set (+0.17 stops) halfway between the green filtered (+1 stop) and red filtered (-.67 stop) brightness adjustment settings used:
Here is what the stage lighting looked like about forty-five seconds earlier:
A few minutes later, after I'd moved to the other side of the stage, the stage lighting was predominately blue but the red cans were also on and the guitarist was being illuminated by a white spot from the tower out in the field.
So just how many color filters would I have needed and how much time would I have spent swapping them out every time the lights changed? Out of about 87 images I edited and published from the set, I used monochrome on 13 of them. Of those 13, I used the following five filter choices followed by the number of images I used that choice:
- None - 1
- Yellow - 2
- Orange - 1
- Red - 4
- Green - 5
Red and green are pretty much polar opposites. What a red filter darkens the most, a green filter barely affects. What a green filter darkens the most, a red filter barely affects.
Beyond that there are some other things in the question that should probably be addressed:
This means that any particular pixel is sensitive to only one particular frequency, and overall, there is a bias towards green light.
This is not really true at all. It's a gross oversimplification many people make. The color filters in front of a digital sensor are much like the color filters we used to use with B&W film. Just because I have a red filter in front of the lens does not mean only one wavelength of red light gets through. It only means a higher percentage of the photons vibrating at the wavelength for red get through than the percentage of photons vibrating at other wavelengths. But some of all of them get through.
Let's make a B&W image of two vases. One is blue, one is orange. They are both about the same brightness under daylight.
- If we take a photo of them with panchromatic B&W film they will both turn out about the same shade of grey.
- If we take a photo of them with panchromatic B&W film, use a blue filter, and adjust exposure slightly brighter to account for the filter, the blue vase will turn out about the same shade of grey as in the first image, but the orange vase will be darker. But it probably won't be totally black, either. Nor will all of the yellow, red, green, magenta, etc. objects in the scene be totally black because we placed a blue filter in front of the lens. Colors will be reduced in brightness with the amount of reduction based on their 'distance' around the color wheel from blue, but you'll still see those objects in the picture. They'll just be darker compared to the blue vase than they actually are.
- If we take a photo of them with panchromatic B&W film, use an orange filter, and adjust exposure slightly to account for the filter, the orange vase will turn out about the same shade of grey as it did in the first photo but the blue vase will now be darker. But it probably won't be totally black, either. Ditto for objects that are yellow, red, green, magenta, purple, etc.
Look at the sensitivity curves for RGGB sensors. They're not that much different than color filters used in B&W photography. A good bit of red and some blue light makes it through the green filter. A good bit of green light and even a little blue make it through the red filter. Even a tiny bit of red as well as a bit more green make it through the blue filter. For a very detailed discussion of how all of this works please see: RAW files store 3 colors per pixel, or only one?
For how using Bayer masked sensors mimic the way our eyes (which, by the way, also use only a portion of the total light that falls on each "R", "G", or "B" cone in our retinas) and brains work to create color, please see: Filter for RGB separation and its effect on the image
However, with black and white film, all the crystals are sensitive to light. I don't know if they are biased towards any frequency in the visible spectrum.
All of the crystals are sensitive to light, but they are nowhere near 100% efficient, either. As to bias towards different portions of the visible as well as some parts of the non-visible portion of the electromagnetic radiation (EMR) spectrum, different types of film respond in varying amounts to different wavelengths. The earliest emulsions used in the mid-1800s were, for the most part, only sensitive to blue light. Now we have what is called 'panchromatic' B&W film that is more even in its response to most of the visible spectrum.
We also have X-ray film that is sensitive to wavelengths of EMR that our eyes can't see at all. We have types of film that are sensitive to UV or IR wavelengths just on either side of the visible spectrum. There's no fundamental difference between X-rays, radio waves, microwaves, and visible light. We call the portion of the total EMR spectrum that elicits a chemical response in our retinas "visible light" only because that portion of the EMR spectrum is what we can see!
My question is, aside from ISO, sensor/negative size, how does black and white film stack up against digital images that have a black-and-white effect applied to them?
There are still a few ways B&W film exceed the capability of digital sensors. At low sensitivities (which are created using less efficient crystals in the emulsions), B&W handles highlights near the point of full saturation a lot better than digital does. On the other hand, digital has progressed to the point we are shooting at sensitivities and getting usable results at ISOs that has never been possible with B&W film in any format size remotely as small as 36 x 24 mm.
In the end you can't really say that either B&W film or digital imaging can do everything the other can. They're two different ways of recording light. There will always be differences in the way each works that will affect how well each is suited for a particular task.
Monochromatic film had its heyday for about a century, during which time it advanced tremendously. Color film, which is basically three monochromatic layers tuned to be most sensitive to three different sections of the visible spectrum, had its heyday for about half a century. Digital is still fairly young in its development. Yet it already exceeds the capability of B&W and color film for many, perhaps even most, photographic purposes. I wouldn't bet against it.
