In physics (and photography is a practice of physics) one of the general rules is: there's no such thing as a free lunch. It's that squeezing of the balloon that I talked about in a previous thread. In general, what you do to fix one problem creates another.
bladefixation2 said:
You can filter out color casts from artificial
light sources using various filters.
Yes. But, these filters reduce the brightness of the light and you end up needing more light.
Some digital cameras let you adjust this 'in camera' so you don't need to get a load of filters.
This is the white balance control that I listed as a must-have for cameras intended for knife photography.
But, these controls aren't magic. The old Law of Free Lunches applies to them too. If you try to push them to far, they also eat into the color depth of the picture. And, they're only able to compensate so for and then they reach their limit.
Cheap cameras and cameras with longer battery life tend to reach those limits sooner.
Why? Because inside of your camera, the
analog voltages that represent the color levels (classically there are three, red, green, and blue but some better cameras now have five or more) go from the CCD to an A/D converter that measures them. But, for several reasons, they pass through a amplifiers along the way (cheaper cameras and cameras with long battery life have only one amplifier and share it between all color channels, but this slows down the process of saving a picture). An amplifier is an electrical circuit that implements the mathematical equation OUTPUT = Gain * INPUT + Offset. When you press the white balance button, the computer inside the camera adjusts the Gains and Offsets (one for each color channel) to get all color channels to read the same value which means white. The problem is that you can only move the gain and offset so far. How far? Well that depends on how high the voltage is in the overall system. The higher the rail voltages, the more range you'll have in gain and offset. But getting higher rail voltages costs more and drains the battery.
The other thing to know is that increasing gain increases the noise in an amplifier. So, if I ask the camera to balance a light source that's very, say, red-deficient, then the gain on the red channel gets turned way up. First, there may not be enough gain range to fully compensate for the deficiency. And, second, the more you turn the gain up, the more noise in that channel has. Noise appears in images several ways. One place it is especially noticeable is on the edges of objects. This can affect the apparent focus of your picture causing a picture that is optically in perfect focus to appear less than perfectly focused. And because it's noise, you can't compensate by defocusing optically.
Moving the offset of the amplifier around eats into the amplifier's dynamic range. This translates into reduced color depth.
This also gets us into setting the ASA on your digital camera. A high ASA setting makes the camera more light-sensitive meaning faster exposures and allowing you to use less light. This is accomplished by raising the gain on those amplifiers. Cheap cameras (and those with long battery life) don't have enough gain range to both compensate for a poor light source and implement a high ASA.
In general, set your camera to the lowest ASA and use bright, good quality light so that the compensations introduced in the gains and offsets are as little as possible.
At the same time, you want to use the fastest possible shutter speed in your camera. Slow speeds allow more time for light to leak between cells on the CCD which means that adjacent pixels are affecting each other. Very bad. Increasing the shutter speed means lowering the aperture. And lower aperture means reduced depth-of-focus. So, again, we see the need for very bright lights. Very bright lights allow fast shutters with high apertures.
And let me just add one more time that even the best editting software can not make the proverbial silk purse out of a sow's ear. Editting software can fix one problem, but it always introduces other problems.
The best thing to do is use the best possible light, take the picture right, and edit it as little as possible.
