Originally Posted by morphinapg
Interesting, but as for the parts that are in the negative, wouldn't it make more sense to compensate for that by raising the g and b response curves rather than raising the r curve? When you have -r, and are limited by constraints, usually you increase b and g. But then again, that's talking RGB in the video space again, but I can only talk about what I know. If you raised G and B to compensate for the dip in R, it seems that you would have almost linear RGB, which makes a lot more sense to me.
Okay, I'm sorry but now you're starting to piss me off.
You readily admit that you don't have any
background or understanding of color, color science, or how SPDs of various colors react with whatever sensors or receptors respond to those SPDs.
And you've had several people with deep understanding of color and calibration state unequivocally that you CANNOT use the camera as an objective measuring device for characterizing color. Yet you're still here adamant that what you are doing is in any way more than guessing.
And now you're trying to re-define a century of color science research because it doesn't make sense to you, despite the fact that you readily admit you really have NO idea what you're talking about here.
Which is why you need to calibrate the camera to the correct white point first, before using it as a tool to measure color.
What are you calibrating it to? Are you pointing the camera at another D65 source and aligning it to that? If so, then what happens when you point it back at the TV, with an entirely different SPD? How do you know that the camera will respond to those two D65 sources the same way? You don't know that, and it likely won't. Again, as I said before, the BETTER way and CORRECT way to use a camera is as an optical comparator, and to match the display to the D65 reference by eye
first, THEN use the camera ONLY as an optical comparator on the single TV in question.
Do you understand that there are an infinite
number of sources that are D65? And they can all be totally different, despite being the same
color. The camera will inherently
respond to those different SPDs in different ways in many cases because the camera is NOT a CIE accurate standard observer and NEVER WILL BE. That means that you could have a dozen TVs, all of them PERFECTLY calibrated to D65, and the camera could see them all as different
So, in order to use the camera CORRECTLY, you can ONLY use it to COMPARE colors on a SINGLE display because it's overall SPD will NOT change(very much) based on luminance. So the proper process would be to look at an accurate D65 reference, and align the TV at a particular %stim to that same color of grey by eye
. THEN, you point the camera at the TV, you measure how the camera responds to that particular TV
and use that response to align the greyscale across the display's luminance range. Fundamental to this though, is the limitation that you CANNOT compare D65 from one display or source to another display because the camera likely will respond differently.
No, it's not measuring it in the same way the meters do, but it is measuring it.
WHAT is it measuring? You have absolutely NO idea what it is measuring. All we DO know for certain is that it is NOT measuring color.
Say it with me: A CAMERA DOES NOT MEASURE
A camera only responds to color in an arbitrary way. We cannot make ANY concrete conclusions about what the color actually WAS that the camera was responding to unless you spend a ridiculous amount of time profiling the camera AND what it is the camera is measuring in the first place. One could do that, but it requires spectrometers to do it.
100%/0%/0% is red, if there was any blue or green in there, it is not pure red.
In the video signal, sure. But you could point a camera at a 100% red pattern, or a 100% green pattern and it is likely to return a value like 100%/3%/4% or anything it chooses. You have no idea what it will tell you.
The same goes for white/grey which is 100%/100%/100%. If you get something like 100%/95%/100%, then that's close to grey, but does not have enough green.
Sure, but again what will the camera see? Point a camera at a calibrated D65 display, or several of them, and you will see that on every display it will give you entirely different numbers, and you would be EXTREMELY lucky if you just HAPPENED to get a display that a camera would report as being equal amounts of "RGB."
No, D65 does not have equal energy across the spectrum, but once you calibrate a camera for D65, it will appear as true white, or 100%/100%/100%.
Only for THAT
specific D65. Not for others.
Except when the camera is calibrated properly, it will be close. Yes, the different SPDs will disrupt that slightly (I'll take your word on it, even if it doesn't make sense to me) but it will be close, even if it's not perfect, and close was all I was going for.
Thank you for at least taking my word one something
I have arrived at a color which is close to D65.
Have you? You have no way of knowing. And if you did the comparing by eye, you actually would have greater confidence that they were the same color because your eyes being human eyes are actually seeing color the a human does so you can be assured that you are actually quite close by visually comparing the greys. If you have a D65 reference, do it by eye, THEN use the camera to make your greyscale flat. D65 measurements with a digital camera are NOT portable to other stimuli.
I don't know or currently care about the xy coordinates,
Then WHAT THE F**K? That's the whole point
of achieving a neutral grey! Every color is mapped to xy coordinates. If you want to align greyscale accurately, you HAVE to care about the xy coordinates, otherwise you've lost your marbles completely.
but since the camera is calibrated to display D65 at equal RGB levels, I should be fairly close to D65, even if being outside the error range of a standard calibration, but that's fine for me, for now.
Seriously: just use your eyes. All you're doing here is pretending to use a tool that isn't
capable of telling you what you want it to tell you. And now you're just starting to get annoying because you don't want to accept that fact, and you don't want to put any real effort into understanding why that is.
It may not be measuring xy coordinates, but that's not what I'm trying to do anyway.
Then what are you trying to do? Make a tuna sandwich? WTF?
I calibrate the camera for D65, which means D65 white should accurately be represented as level RGB.
Only for THAT D65, not for others.
Using that, I point it at my TV and attempt to achieve as close to level RGB as I can.
So what will the result be? Will it be D65? NO!
You're better pointing your EYES at the TV and comparing the D65 reference to the display and making them look the same. That way you are actually aligning the TV to D65 and not some arbitrary value which may or may not be D65 at all.
I understand the difference in SPD between daylight and my TV will cause a slight variation in my color, but I also believe that variation won't be big enough for the color to be worse than when I started. As long as I have gotten the color closer to calibration, I have succeeded in what I set out to do. I never planned for this to be an entirely accurate or substitution for a real calibration, but using the tools I already have, without buying further tools, I believe I have gotten closer than I was before, and I believe I have gotten closer than I would have by just using my eyes.
Believe whatever you want. It's a free country. Just don't argue with people who know what they're talking about when they tell you you're wrong.
A camera measures color, just in RGB space (which is a real world color space) and not in xyz. I realize you're used to measuring color in xyz and find it hard to believe RGB could accurately represent color, but it can. It might not be as accurate as xyz, but it's close enough for me for the moment.
NO a camera does NOT measure in CIE RGB space. A camera measures entirely arbitrary values which are denoted as R'G'B' in video and imaging standards, but are NOT CIE RGB values, and you CANNOT derive actual CIE RGB or XYZ values from them.
By the way, I'm still not clear on what SPD represents, other than for some reason it changes the color in a camera and not a meter used for calibration. Is it related to the brightness of the color, or what? I just don't get what it represents.
It's the entire spectrum of light that comprises anything we see. It's the actual stimulus to which our eyes and cameras and color meters all respond.http://en.wikipedia.org/wiki/Spectra...r_distribution
The following images (and more) can all be found here:http://www.gelighting.com/na/busines...ion_curves.htm
Here's the SPD of a D65 flourescent:http://www.gelighting.com/na/busines...ution/SP65.jpg
Here's the SPD of a daylight bulb:http://www.gelighting.com/na/busines...n/daylight.jpg
Here's the SPD of some daylights:http://www.gelighting.com/na/busines...r_daylight.jpg
How our eyes will react to those versus a camera could differ considerably
. And the SPDs of various display can vary HUGELY depending on the light source. A phosphor, versus an HID lamp, versus an LED, etc are all VERY different, that even properly designed colorimeters (let alone far inferior cameras) run into significant problems which is why on some display you really have to be using a spectrometer.