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View Full Version : White balance - just what is it?



Puffer Fish
11-26-2007, 06:10
This is the other big issue with digital photographers, setting the correct white balance.

Tonight, I will show examples and go thru the math, but here is the deal.

In the digital world, "adjustments" are math calculations. Sometimes complex math, sometimes easy math, but they are just math.. nothing more, nothing less.

Actually, even the ISO numbers are just calculations being done by the camera... the sensor did not change.

The objective of setting a white balance is to have accurate color... color, by the way, defined by the some picked value, like mid day sun, or 5,000 k, for example.

To the photographer, they are measuring a white and then the camera is correcting their images back to the color it would be in this ideal lighting. Seem pretty simple and fairly important.

First off, underwater, the color of the lighting changes with the distance you are from the object and the depth. This is really, really true when using a strobe, as the light has to go out and come back, so every foot is actually 2 feet of difference.

That means, if you want to set you white balance accurately, you need to set it for the conditions of each photo... if they are all the same, the one setting will do, if not, then more adjustments will be needed.

So how does it do it? Well, the camera takes what you give it as white, measures the difference between that and what it has for a standard, and applies a formula to all of the pixels. It is not a plus or minus formula, but one for a curved line (more on this later). Black stays black... pure white stays pure white, and all the numbers inbetween change by the formula, so that the white image now matches the stored standard.

People will then say " I know it does not match all the different pictures I am taking, but it is better than doing nothing. A very valid point, by the way.

But there is a better, more accurate way.

Any good software has built into it that can do the identical thing... as well as means to do the same measurement the camera makes.

All you need to know is the correct color of the "white" in question and then just take a picture with that white in an image...change depth... take another picture... change distant, take another picture.

The big advantage to this, is that you can do the adjustment picture, after the fact.

Say a whale just happens to swim by... and you take a picture... after it passes, you have someone hold the white sample from the same distance and correct the image.

There is one other giant advantage, the white sample is never actually exactly the same color as the stored standard in the camera... but in this system, you adjust to the actual targets color.

This is not without it's issues, by the way... as sometimes, the calculation is not correct, and the colors are actually off. Interestingly, this happens with both incamera and out of camera adjustments. But out of the camera, you will know what the issue is.