In my blog for beginning DSLR camera users, Hub's Camera, the topic of setting the proper white balance was the subject of a three part post (Parts 24a, 24b and 24c). It is also possible to correct an image's white balance in the digital darkroom after the picture has been taken. Regardless of whether you decide to address the issue of white balance when taking the picture or later in your computer as a "post processing" procedure, white balance is critical to the accurate rendition of colors in the final picture.
Figure 1, A classic white balance situation
Figure 1 illustrates the white balance problem faced by photographers in different light source situations. The image on top was taken with the camera set to "daylight" white balance. The colors in this picture have a definite yellow and red cast. This result is to be expected since the predominant light source for this picture was a table lamp with a standard tungsten light bulb.
The lower picture in Figure 1 appears more "normal" to our eyes. The whites are white. The blacks are black. And all the other colors are very close to the originals. To accomplish correct color rendering, the camera was set to a white balance of "tungsten". With the white balance settings on "tungsten", the camera automatically applied adjustments to make the final image look "normal" -- as it would appear under natural sunlight conditions.
So, that works pretty well. But what about the times when:
- a photographer forgets to change the white balance settings in the camera, or
- the available light source isn't quite a match for any of the camera's built-in white balance controls, or
- the photographer needs to further refine the white balance of an image for precise color rendition?
This is the first of a two-part discussion on White Balancing a picture after it has been taken using a digital imaging program. I will present the underlying principles that determine proper light balance. Understanding white balance requires an understanding of neutrality and a known point of reference. Sounds technical, but it's really common sense explained using a little technical background information.
Photography is a Red, Green and Blue world -- the world of primary colors. Using these primary colors we can reproduce all the colors we see in the real world every day. We can accomplish this because digital photography allows us to control the amount of red, green and blue that makes up each and every point of color in our final pictures. Every point of color in a picture is expressed as a specific amount of red, green and blue, in increments up to 256 for each color.
To illustrate this concept, hit the play button on the video screen below.
Figure 2 - RGB video
I know. I know. I'm no James Earl Jones. But I hope the information shown in the Figure 2 video helps you understand how all the colors of the rainbow can be re-created in photography by using only three primaries -- red, green and blue.
Figure 3 - Neutral Gray numeric values
Most importantly for our discussion of white balance correction, let's look at the concept of a "neutral" gray. A neutral gray has no color bias. A true neutral gray of any density contains numerically equal amounts of red, green and blue as shown in the Info screen in Figure 3.
Why is neutral gray so important? Glad you asked. In reality, there are few colors in a real photograph that we can identify by their RGB numeric values. Agree? When you take a picture of a red flower, do you absolutely know the R, G and B numeric values of that flower's red coloring? No. It's impossible without carrying around a scientific color measuring device in your camera bag. Let's not do that.
There is a component within a picture about which we do know some facts that will allow you to correctly color balance your image. That's the colors black, white and all the grays in between. We KNOW that if these "colors" are reproduced accurately then the Red, Green and Blue numeric components will be identical. If you can identify a white or gray in a picture, you have found a "known reference". That's a point of reference that can be used to white balance your picture and render the final image as it would appear under normal daylight lighting.
Then all we have to do is apply photography's best kept secret. If you can correct that shade of gray to a true neutral (where RGB values are identical) and change ALL remaining colors by the same amount, every color in the picture will be rendered correctly. Remember: When you identify a "known reference" and adjust that one color (gray) to neutral, then all the other colors will look correct.
Part 24b will discuss the tools that software programs like Photoshop and Lightroom 2 provide to make this critical white balance correction. You've already done the hard work by working your way through this post. The actual adjustments you will learn in Part 24b are easy.
Figure 3 - Neutral Gray numeric values
Most importantly for our discussion of white balance correction, let's look at the concept of a "neutral" gray. A neutral gray has no color bias. A true neutral gray of any density contains numerically equal amounts of red, green and blue as shown in the Info screen in Figure 3.
Why is neutral gray so important? Glad you asked. In reality, there are few colors in a real photograph that we can identify by their RGB numeric values. Agree? When you take a picture of a red flower, do you absolutely know the R, G and B numeric values of that flower's red coloring? No. It's impossible without carrying around a scientific color measuring device in your camera bag. Let's not do that.
There is a component within a picture about which we do know some facts that will allow you to correctly color balance your image. That's the colors black, white and all the grays in between. We KNOW that if these "colors" are reproduced accurately then the Red, Green and Blue numeric components will be identical. If you can identify a white or gray in a picture, you have found a "known reference". That's a point of reference that can be used to white balance your picture and render the final image as it would appear under normal daylight lighting.
Then all we have to do is apply photography's best kept secret. If you can correct that shade of gray to a true neutral (where RGB values are identical) and change ALL remaining colors by the same amount, every color in the picture will be rendered correctly. Remember: When you identify a "known reference" and adjust that one color (gray) to neutral, then all the other colors will look correct.
Part 24b will discuss the tools that software programs like Photoshop and Lightroom 2 provide to make this critical white balance correction. You've already done the hard work by working your way through this post. The actual adjustments you will learn in Part 24b are easy.
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