I might add...
The main issue with photos not withstanding the obvious ones already pointed out is the array of varibles along the whole path.
Consider; for the viewer to see the result as the original observer all stages must be at the same reference. ie Calibrated.
All these stages have to be at the same reference(what ever chosen).
1.Source material/Player output
2.Projector/screen
3.Camera
4.Computer/screen(data crunching)viewing
5.Computer/screen at final viewers end.
Any experiment that is considered real is repeatable, a one off occurance is really an indicator read wrong can lead one astray.
1. Although many use calibration DVDs as a source, alot dont. Mistake one. Reference material must be used. Then the player, how accurate is yours? Mine truncates 10% off the bottom end, which I didnt know until I referenced it against a video generator. I know not everyone has a video generator at hand , but you get my point. Minimalise the in accuracies by using reference DVDs.
2. This is more complicated. Alot dont do a full calibration(greyscale). Alot do. But what to calibrate too?
The PJ direct, so iliminating the screen surfaces? Feasibly the best to show a camera shot, however I proved to myself that this also doesnt work for the reason that until each surface as a reflection is calibrated the surface is not at its full potential.
The is the fundemental issue with screen shots!
I actually found that calibrating to each surface under experiment then photographing each of them with the same parameters(exposure, ISO, fstop and so forth(no white balance,ill get to that).Then cut up the photos in the PC so one can compare each surface to the same reference visually. This yielded the best image differences.
3. The white balance on a camera. How many know you can calibrate a camera? (a bit like calibrating a printer). The overall white balance can be the least of the cameras issues.
Anyway, I asked a semipro top photographer here(wildlife) about how he would shoot screenies.
He said the problem with doing a white balance on the fly is that one can be off distorting the captured raw material. Alot of cheap/mid priced cameras don't offer RGB white balance, only predifined white balances which are generic.
Here he said it is best to use your PC graphic programe to set the white balance. (of course you need a reference card or white balance material shot). Capture the shot as is, concentrating on getting the exposure time correct with the least noise(digital noise). Use those built in histograms to get the exposure right. I always use ISO80 setting with long exposure to get less noise for example.
I tend to agree with his theory. Others may not, but i found his method fruitful.
4. Calibrate the monitor/PC. The meters bought for calibrating your Projector is designed for PC's...use em.
5. If you the final viewer has a meter for calibrating and you havent calibrated all the pc's in your home, shame on you
I do more PC calibration than home theatres, most are blown away how monitors compare before and after.
As you can see(pun) the varibles can add up, so what are you really looking at? what is someone else seeing relative to you?
In some ways you can compare some relative differences, however one has to trust the original observer in their observations which one can easily be led astray by enthusiasim(not directed at anyone, a general comment).
Overall the above issues are the reason why numbers measured with traceable equipment to known references remove error and varibles. One has to visualise of course what this means.
Screenshots really document proceedures and show proof of work.
