The importance of setting the right white balance
Have you ever though, why do we need an accurate white balance value? Generally it seems so irrelevant. In this article you will see why this seemingly un-important variable is so important for us photographers. Without having an accurate white balance it is just not possible to get color and contrast set correctly. For example people calibrate their PC monitors, spend hours editing images, while ignoring or not realizing the impact an incorrect white balance can have on the image.
The above illustration shows what happens when the “image” signal enters the camera. First it passes through the lens, then into the camera body, next signal pass through a RGB filter that is placed on top of the sensor and then it hits the image sensor. Typically in our own minds we think of an image in color and most people never realize that the camera sensor only reads a black and white image signal. To better understand how the camera go about preparing the b&w image for the sensor, lets have a closer look at what really happens from taking the image, too saving it on disk.
The process is in fact very basic. Placed above the sensor is a RGB or Red, Green, Blue filter. Its a fixed filter with known characteristics that cannot change. As the image signal passes through the RGB filter, on its way to the sensor, the filter removes all the green, red and blue color information from the incoming image signal. What reaches the sensor is only colorless light. The sensor cells are simply sensitive to light, so in that sense the sensor produces a b&w image only. This black and white image is then saved in the camera memory as a "sensor" image before its saved on the memory card.
To rebuild the color image for that what is on the sensor, the camera requires the image white balance information, the RGB filter data and the sensor b&w image data. The white balance value is a measured value. High end cameras for example use build-in white balance sensors. All these separate pieces of data is refer too as the RAW image data or the digital negative.
With this RAW data the camera or the external RAW image converter in your PC can rebuild the original color image. Keep in mind the only variable in the image rebuilding process is the White Balance (WB) value. That is why its so important to use an accurate and correct WB value.
Some cameras guess the WB value based on image recognition samples it has build into its memory. Other more advance models like the E3 from Olympus read the WB value with an outside sensor that is fitted in the camera body.
Each time a new camera model is released the first improvement manufacturers like to talk about, is a better image processor. Olympus name their image processor Truepic, Sony name their's Boinx and Canon use the Digic processor. It is the function of these processors to record the measured white balance information that will be saved with the RAW image. It is also these processors that will rebuild the RAW image into a 8 bit JPEG color file. This color file is then saved on the memory card.
How does one see a false WB?
Many would say, the image color will not be right. Although 100% correct, the said answer does not paint the full picture. Pictures or scenes can have many small color variations or nuances that all contributes to painting the feel and atmosphere of the final picture. Take for example a beautiful sunset mixed with rich colors. If the WB is out the sunset will loose a lot of its impact.
When the camera or PC program re-build the color image, it is just impossible to recreate these small color nuances in a image if the WB information is incorrect. Color casts is another classic result when the WB information is not correct. What we see when looking at a typical RAW converter like that of Bibble or Adobe, is that the WB setting consist of a Kelvin color temperature slider (value) plus a hue slider (value). If the WB setting had only one variable (slider) then it was easy for us to seek the right value by moving the slider in the editing software left and right until one find the right position. As said white balance adjustments really has two or more settings. That makes it nearly impossible to adjust white balance using trail and error. Its so important to practice adjusting or setting the white balance correctly.
How does one set WB correctly?
One can set the white balance while doing the photo shoot or one can correct the WB during the post processing stage. In both instances one can make use of a measured white balance (WB) value, for one image only, or a group of images. The following bullets describe how to record and save a "good" white balance value:-
Use a gray card to record and set a unique white balance value in the camera.
One can also set the WB value in the camera by selecting the clouds setting when its cloudy or sun for a sunny day ext. This works especially well indoors.
One can also use the "Cube" made by the company, Spider. The cube has three setting, black, gray and white. That makes the cube a very accurate tool.
My own preferred method is to first take a WB reference image whenever the light conditions change. Simply place your gray card on the "right" spot in the scene and take a reference image. Then remove the gray card and continue taking pictures.
All the reference image does, it makes it easy for us to use a correct 18% gray spot in the image to adjust WB with in the editing software. If one did not take a reference image then one can use the image editing software to find and correct the white balance of the image. Each RAW converter has a so called WB pointer. If you do not use RAW files yet then you can use the WB pointer in the curves function. This WB pointer the photographer can use to point to an 18% gray spot in the image or to a white spot in the image. There are a few basic guidelines one can use to find the right spot if you did not shoot a reference image. In Photoshop one can use a specific technique to determine the so called 18% gray areas in the image.
Another method to edit or adjust the WB is to make use of the histogram. For best results, when adjusting WB with the histogram is to adjust each color channel separately. The final method is to train your eyes. As one gain experience editing images, one also learn how to correctly or best use the WB pointer. Remember one can use the WB pointer in Trail & Error mode. The reason is the pointer adjusts all the WB variables in one go when the WB pointer is pointed to the right area in the image. Using this method also helps finding exactly the ambiance you were looking for.
What I learned over a long period of trail and error is that it is so important to use your own discretion. The reason is that the color temperature is not the same or consistent throughout the image. The image white balance will change in the areas filled with direct sunlight or it will be different in the shadow areas or it will be different again in areas with artificial light. Which of these areas will become the right sampling area?
Too often we as digital photographers seek ways to do the correct thing and we completely forget that we are artists. Please do not get caught in the www, Web standard where individuals try and place limitations on artists. Photography has many aspects, some are distinctly technical and others are the fun and artistic.
Having said that I like to point out an interesting fact to you. No matter where you point the WB pointer in the picture, the software will always calculate the best hue and color temperature combination for that sample area. At this point it is the decision of the photographer to select a sampling area. In the picture below one can take a sample in the "white" snow that is in full shade. That will warm up the image. Taking a sample in a area that has direct direct sun light will give a cooler tone to the image. The final decision will be that of "experience plus practice".
White balance will determine the final look and feel of your images. White balance can be the difference between a dull looking "digital" picture or an image that really jumps at you when looking at it. Its true that WB is only a part in the final workflow discipline each photographer develops. Fact is the impact it potentially has on an image is huge.
As we discussed in this article, white balance has a lot behind it plus one can quickly turn it into a technical pain or one can use it as a powerful tool to express your own artistic signature. The road to having a powerful signature is practice and experience. The fun part is that the reward is significant and its by far worth the effort........