In Part 1 of this series on White Balance we defined WB and in Part 2 talked about using WB to control the colors in our images. If the WB setting matches the color temperature of the light hitting our scene we would get accurate rendering of the colors in the scene. And if the camera WB setting did not match the color temperature of our light source the image would be rendered with a color cast. And that as creative we photographers sometimes want to purposely shift the colors in the image to control the emotional content of the image.
You may have noticed that in Part 1 the example images had the WB set at the time of capture and that the example images in Part 2 had the WB adjusted during post processing (during the raw conversion step). This leads to the question, “What is the best time to set WB and are there any advantages to doing it during capture or in post production?” The answer is that it depends on the file format you are capturing your images in, jpg or raw. But before we answer the question lets take a look at the differences between jpg files and raw files.
The jpg file that comes out of a camera is nothing but the same data that would have been saved in the raw file that is run through the raw converted built in to the camera. When the camera does this built-in raw conversion it uses the camera’s settings for WB (as well as saturation, contrast, sharpening, etc.) but it does not save the raw data. If a jpg image has a slight color cast it can be adjusted in post processing using image editing software like Photoshop. When this is done the numbers that represent the red, green, and blue tones for each pixel in the image are modified. Without going into all the technical reasons jpg files do not respond well to extreme adjustments of color.
The raw file that comes out of the camera is simply the tone of one color; red, green, or blue, for each photo site on the sensor. Technically speaking this is not an image file. In order to make it an image file it needs to go through several processing steps one of which is call demosaicing. This is where the tone values for the other two colors is added to turn the values for each photo site into a pixel. That is; the raw file only has the tone value for one color and the demosaicing process interpolates the tone value for the other two colors, making it a pixel with tone values for red, green, and blue. (Here is a link to a tutorial on the Cambridge in Colour site if you want to know more about how raw files are converted into image files.)
Now back to the original question: Is it better to set White Balance correctly during capture or to not worry about it in the field and set it in post? If you are capturing your images in the jpg format then you are much better off getting WB set properly at the time of capture. If you are capturing your images in the raw format you can pretty much leave the WB setting to Auto and fine tune the WB setting during raw conversion. The reason I said “pretty much” is there can be times when it is advantageous to set a specific WB during capture of raw files.
If you recall from above, the raw file is not an image file. In order to provide the preview for the image, the camera creates a jpg with the camera setting applied (this does not affect the image data in the raw file). The histogram displayed on the camera’s LCD is based that jpg with those camera settings. And adjusting the WB can affect the exposure (histogram). (The next time you have an image open in a raw converter look at the histogram while adjusting WB.) If proper exposure is critical, the histogram will give more accurate information about exposure when the WB is set close to where it will be set during post processing.
The other time it can be useful to set a specific WB when shooting in the raw format is when you know you will be using WB creatively–that is, using WB to purposely render the image with a much warmer or cooler color cast. In these cases it will be much easier to make judgements about the composition when looking at the preview if the color is closer to where you want it rather than closer to the scene’s actual color. As noted in Part 2, a Tungsten WB will render a neutral scene very blue (cool) and a cloudy WB will render a neutral scene very yellow (warm).
Since there are times when setting specific WB during capture can be helpful, for both jpg and raw files, in the next part of the series (the last part I think) we’ll look at how to determine which WB setting to choose and take a look at setting a Custom WB.