I am back for another quick article. This is the subject of white balance, and could be the difference between good shots and great shots. This I found to be the trickiest off all things to get right at a FRC event and the most overlooked in shooting. The problem is that the field is typically lit by very hot, bright lights while outside the arena it is lit with a cooler mix of lights with tungsten, fluorescent, and natural light seeping in.
The problem is this, the environment absorbs, reflects, and takes on the personality of the light source. A light that is skewed toward the blue end of the spectrum will cause the scene to appear blue. A white piece of paper would look blue, but our brains tell us that we know that the sheet is white so we trick ourselves into compensating for this blue cast. Take a picture of the same scene and the camera will show you exactly how the scene looked at the time it was taken turning a perfectly staged scene into a group of lifeless zombie corpses (Bad] as opposed to Good]). The same can be the case if the light source is skewed reddish which tends to wash out all the color to where nothing in the scene pops (Bad] as opposed to Good]) or (Bad] and Good]).
Take a look at an FRC event and you notice that there are many light sources lighting the same subjects in the scene. The main field lighting originates from rows of par cans on either side of the field suspended by the field truss. But, look around and there are plenty of other light sources to throw off the scene. These can be outside light seeping in or a mix of house lights. This causes a lot of trouble because the subjects take on the character of each light source. It may be impossible to compensate for everything in the view of the camera. I have found that it is just best to try to limit the amount of light sources in the scene as you can see in this photo the subjects are lit by house lighting but the background is saturated by natural light that is hotter resulting in the blue background Pic].
Some times there is nothing you can do about the lighting situation. For example, the large displays are lit by even hotter HID bulbs. Take a look here and notice that the area around Delphi has a blue cast. Pic] Correcting for the cast in the sign would have created a red cast in the rest of the image which would be even more noticeable. Correct for the primary subject in the field of view.
Some cameras are better than others in automatically correcting for lighting conditions. In a challenging lighting shoot like at a FRC event I mainly do not take my chances and do not use the auto white balance. For some cameras the sunlight setting is a good ballpark value for the main field and the tungsten setting is all right for the pit areas which are typically lit by house lamps. Using the built in settings makes it easier to shuffle settings between areas.
Many cameras allow you to manually compensate for the lighting conditions by shooting a blank pure white sheet of paper under the light your subject is under. If you tell the camera what you are shooting is white it can calculate the delta of how off the shot is and compensate for it. This does not work well in practice, however. The field will probably get mad if you go out on the field to shoot a blank piece of paper, and who carries a stack of paper with them anyway? A better approach is getting yourself a white balance filter. (http://www.digitalphotographykits.com/whitebalance.htm) It is a diffuse lense calibrated to pure white that you can just point at the dominant light source and hit the color correct button on your camera and you are done.
Another trick is if the image is fairly close but there is a little bit of a hue, and it is the perfect shot that you would like to print (minus the hue) it can be “fixed” in a number of post processing softwares. The main process is to identify an area of the photo that is pure white, pure grey, or pure black. It is fortunate that the referees shirts are white and black, since they make a great color reference. Also, the carpet on the field is normally grey. I occasionally take a couple loose strands of the carpet as a reference that I can hold up to the screen and match the picture to it. Note that this can only correct for minor color variances because a strong hue will loose color information from the other color components that it is over-saturating, so some photos just cannot be fixed unless you shot the photo in RAW format.
If your subjects are real close, you can generate your own light source with the camera flash. For example Bad] or Bad] as opposed to Good] or Good].
I do not find much use for a flash at most competitions. First, even the most powerful portable flashes will not give you the distance or field coverage really required without spending some real money. Also, even if you were using it for an effect such as opening the shutter slightly before the flash of a robot racing down the field. That would give you a streak blur and a crisp image of the robot. However robots are mainly metal and glares unnaturally even under a diffuse flash. Flashes work best with diffuse subjects such as people, but then create a whole new problem of red eyes, hot spots, and such.
One instance where a flash can work is if you are trying to overcome a significant back light such as Bad] as opposed to Good]. Though notice the red eye that should be post processed out. Try to surprise the subject so they are looking away to create a more natural looking scene and to avoid red eye from the retina reflecting the flash directly back to the camera Better].
Another is to de-emphasize the background in a shot by overpowering it with a strong light source in the foreground. Bad] as opposed to Different].
Who knew there was so much to white-balance! Tomorrow I can post some more opinions on EVs, dynamic range, and lenses or answer any questions if anyone is interested….
-J
