Heidi in Black and White

Heidi in Color

Being a professional photographer with a technical background, I often get asked photography questions that are technical in nature.  Some of the most frequently asked questions include “Why does aperture affect depth-of-field?”, “How do I photograph an all-black dog?”, and “Why does focal length affect perspective?” (short answer to the last questions: “IT DOESN’T!” it’s a trick question that requires a trick answer) I’m going to start writing a series of articles that answer some of these questions, in as plain of language as I can make it.  But instead of a highly technical question, I’m going to start of with more of a philosophical question that in my opinion requires a technical answer:

Is turning a digital color photo into black-and-white cheating?

The answer to that question isn’t exactly, well, black and white. 

First, let’s examine the way a digital camera records an image:

The image sensor inside a digital camera is essentially “color blind” and can only detect the brightness of light it receives, not its colors.  (The Foveon X3 sensor is a notable exception, but unfortunately the sensor has not been a commercial success and only a small percentage of photographers use cameras with this sensor).  So without some clever engineering tricks, a digital camera is only capable of taking black-and-white images.  The clever engineering tricks come in the form of a “color filter array” that is put in front of the sensor.  The most commonly used is the Bayer Filter, pictured below:

Courtesy wikipedia.org

For each photosite (or pixel), the filter blocks out all but one primary color (Red, Green, or Blue) so only the brightness of one primary colored light is recorded.  For sensors using the Bayer Filter, this means that 1/2 of the pixels record green lights, 1/4 record blue and 1/4 record red.  The reason for having twice as many green pixels than the other colors is that this more closely mimics human eyes, which are more sensitive to green than they are to blue and red.  Various software algorithms (depending on the camera maker and model) then take “educated guesses” to fill in the missing two colors at each pixel.  For each color image, what’s recorded are actually 3 black-and-white images, each representing one of the primary colors.  For example, below are the 3 black-and-white images that make up a color photo of Louie:

Red

Green

Blue

If you look closely (click on each image to see them bigger), you’ll notice that the image labeled “Green” has the brightest grass and “Blue” has the darkest grass because grass contains a lot of green and very little blue.  By coloring each image red, green and blue respectively as follows:

Red

Green

Blue

and adding the three images together, we end up with:

Louie in full color

As you can see, when you take a color photo with a digital camera, you’re essentially taking 3 black and white images at the same time, each one with a different colored filter.  This allows the photographer much greater creative freedom when turning the color images into black and whites.  I will go over the editing process a little later.  Photographers shooting with black and white film often put a color filter in front of the lens in order to manipulate the contrast.  A blue filter, for example, will brighten the blue sky and a red filter will do the opposite.  A digital color image gives you both of these options simultaneously and automatically, plus a third one with a green filter.  I’m not an Ansel Adams expert, but I can’t imagine him saying no to having these options if they were available to him!

Should I use the “Black and White” setting on the camera?

That depends on what you intend to do to the photos after you take them.  If you’re serious about black and white photography and want to get the most of the images you shoot, however, the short answer is “no”.  When you use the “black and white” setting on your camera, the camera decides for you (through computer algorithms that are different for each camera maker and model) the “best” way to combine the three black-and-white images that it took to make one black-and-white final image.  It then records that final image and discards the three original images that it took.  So all that information that may be useful to you in the three original black-and-white images is lost forever and can’t be recovered when you use the “black-and-white” setting.  Here’s a very simple but exaggerated example.  Suppose you were to take a photo of a red, green and blue pattern pictured below:

the three stripes, although of drastically different COLORS, are of the same BRIGHTNESS.  If you used the “black-and-white” setting in your camera to take the photo, you’re likely to get this:

This is the “correct” black-and-white image based on brightness, but it’s not at all what you’d expect to see, knowing that the three stripes have different colors.  If you took the same photo in color, there is then the opportunity to manipulate the image later to obtain the black-and-white image you expect to see, which is an image with three different shades of gray:

The above image is obtained by subjectively making blue darker than red and red darker than green.  But that’s just one way to interpret these colors.  The image below, which makes red darker than blue and blue darker than green would be just as valid:

So which color appears as which shade of gray is entirely up to the photographer’s interpretation.  This is where the creative freedom comes into play.  If you used the “black-and-white” setting on the camera, you would’ve gotten a solid gray image and lost the opportunity to exercise that freedom.  This process of selectively brightening and darkening of colors to obtain black-and-white photos actually allows much more creative freedom than color photography, since when we view a color photo, we have an expectation of what colors we should see based on experience.  When viewing a black-and-white photo, we have no such expectations since we don’t see things in black and white.  The photographer is thus free to interpret the colors however they want when turning the image into black-and-white.

So what’s the best way to make a black-and-white photo out of a digital color image?

A very common tool that a lot of photographers, myself included, use, is the “Channel Mixer” in Adobe Photoshop.  It can be found under “Image -> Adjustments -> Channel Mixer…” its dialogue box is shown below (click on it to enlarge):

Photoshop Channel Mixer dialogue box

This allows you to selectively brighten or darken each of the three primary color, red, green and blue, to obtain the desired black-and-white image.  If you have Photoshop, the best way to learn it is to just have fun and play with it.  Move the sliders around and see what effects they have on your image.

Conclusion:

I hope I have made a convincing argument that turning a digital color photo into black-and-white isn’t cheating at all.  In fact, it’s one of the most creative ways of making a black-and-white photo.  If one simply takes a bunch of digital color photos and aimlessly pushes that “desaturate” button in Photoshop to obtain a bunch of black-and-white photos, I suppose you could probably argue that’s “cheating”.  A black-and-white photo obtained that way probably isn’t very interesting anyway  and the creative process that should go into a photograph was thrown out the window.  But when carefully planned and processed, it is one of the best ways of making a black-and-white photo.