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JRR
I agree with what you say. Furthermore, the precision of the colour from a camera is far from perfect, either.
If you take a 3 CCD camera, for example, it's all done with mirrors. Dichroic mirrors. These are mirrors which theoretically reflect some colours and transmit others. These can be made quite good, but they don't have a precise and sharp cut-off frequency, so they are complemented by primary RGB colour filters. These have a gaussian distribution transmission curve centred on the primary colour, with almost total cut-off about 60% of the distance along the spectrum to the next one. As the tail-off is asymptotic towards zero transmission, it never actually reaches zero. Anyway, there is an overlap which is not entirely negligible and the band-pass width of each is different, anyway.
BTW, you can see this overlap. If you superimpose the three filters, at first glance they appear black, as they theoretically should. However, if you look through them at a bright light (not the sun, because they may transmit IR!), you can see it dimly, usually as a dark red or violet.
However, this is not frightfully important, because the receptors in the eye have a similar overlap, anyway!
Furthermore, the visible spectrum is perceived differently by different persons, as tests at both ends have shown. Youngsters have a slightly wider visible spectrum than us wrinklies, especially to the violet end.
Colour perception is therefore very relative. I used to know a person whose job it was to match colours in knitting-wool dyeing, to try and get batches as similar as possible. He had two colleagues and they used to sit for half-an-hour arguing which adjustments to a dye bath were needed. Although they had colorimeters, these were not as sensitive as these guys' trained eyes. I could never see the difference between the different trials, when one of them was saying that there was too much of such-and-such a colour and another was suggesting reducing the mordant level and so-on.
I have in front of me a Sonnetech Colorific Color Reference Card for adjusting the monitor. It is a piece of blue PVC with some holes in it and you attach it to the screen over a special test pattern. The object is to try and determine which hole is invisible when a special test pattern is displayed. IMPOSSIBLE for my feeble eyes!
Another factor which cannot be ignored is the colour temperature of the ambient light. This can alter one's perception of colour very widely. Most of us don't make any adjustment to our monitors or TVs as the quality of light varies according to the time of day, the weather or the power voltage.
My reaction is therefore not to try and be too perfectionist. If it seems reasonable, it's OK.
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Brian (the terrible)
I agree with what you say. Furthermore, the precision of the colour from a camera is far from perfect, either.
If you take a 3 CCD camera, for example, it's all done with mirrors. Dichroic mirrors. These are mirrors which theoretically reflect some colours and transmit others. These can be made quite good, but they don't have a precise and sharp cut-off frequency, so they are complemented by primary RGB colour filters. These have a gaussian distribution transmission curve centred on the primary colour, with almost total cut-off about 60% of the distance along the spectrum to the next one. As the tail-off is asymptotic towards zero transmission, it never actually reaches zero. Anyway, there is an overlap which is not entirely negligible and the band-pass width of each is different, anyway.
BTW, you can see this overlap. If you superimpose the three filters, at first glance they appear black, as they theoretically should. However, if you look through them at a bright light (not the sun, because they may transmit IR!), you can see it dimly, usually as a dark red or violet.
However, this is not frightfully important, because the receptors in the eye have a similar overlap, anyway!
Furthermore, the visible spectrum is perceived differently by different persons, as tests at both ends have shown. Youngsters have a slightly wider visible spectrum than us wrinklies, especially to the violet end.
Colour perception is therefore very relative. I used to know a person whose job it was to match colours in knitting-wool dyeing, to try and get batches as similar as possible. He had two colleagues and they used to sit for half-an-hour arguing which adjustments to a dye bath were needed. Although they had colorimeters, these were not as sensitive as these guys' trained eyes. I could never see the difference between the different trials, when one of them was saying that there was too much of such-and-such a colour and another was suggesting reducing the mordant level and so-on.
I have in front of me a Sonnetech Colorific Color Reference Card for adjusting the monitor. It is a piece of blue PVC with some holes in it and you attach it to the screen over a special test pattern. The object is to try and determine which hole is invisible when a special test pattern is displayed. IMPOSSIBLE for my feeble eyes!
Another factor which cannot be ignored is the colour temperature of the ambient light. This can alter one's perception of colour very widely. Most of us don't make any adjustment to our monitors or TVs as the quality of light varies according to the time of day, the weather or the power voltage.
My reaction is therefore not to try and be too perfectionist. If it seems reasonable, it's OK.
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Brian (the terrible)
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