Post by anfieldude on Nov 19, 2012 9:02:43 GMT 8
Display Calibration – Whats and What Nots….
Calibrate/Calibration
Wiki Definition:
Calibration is a comparison between measurements – one of known magnitude or correctness made or set with one device and another measurement made in as similar a way as possible with a second device.
Cambridge Definition:
Describes tools or other devices that are moved slightly or have marks for making accurate measurements
FreeOnline Dictionary Definition
1. To check, adjust, or determine by comparison with a standard (the graduations of a quantitative measuring instrument):
ISO Definition:
Calibration quantifies the relationship between the readings of any meter, weighing balance, mass spectrometer or graduated cylinder and the relevant units in the SI system. Paraphrasing the formal definition in the VIM, the instrument’s readings are compared to the values of a measurement standard under controlled and specified conditions
My Definition:
To compare an instruments performance to a pre-defined standard under a pre-set condition and make changes to the instrument (when possible) to achieve the said standard.
Calibration - The act or process of calibrating or the state of being calibrated
Now that we have the definitions out of the way, we can move on to the next portion of the article.
I would like to talk about an area that I believe is instrumental in Display Calibration.
The study of how film is captured, transformed for theater and then subsequently home cinema.
To understand all this we need to understand our eyes. Our eyes are the windows to the world that we see.
The Eye….
Reference Hecht, 2nd Ed.
Sec. 5.7
The retina contains two types of photoreceptors, rods and cones. The rods are more numerous, some 120 million, and are more sensitive than the cones. However, they are not sensitive to color. The 6 to 7 million cones provide the eye's color sensitivity and they are much more concentrated in the central yellow spot known as the macula. In the center of that region is the " fovea centralis ", a 0.3 mm diameter rod-free area with very thin, densely packed cones.
The experimental evidence suggests that among the cones there are three different types of color reception. Response curves for the three types of cones have been determined. Since the perception of color depends on the firing of these three types of nerve cells, it follows that visible color can be mapped in terms of three numbers called tristimulus values. Color perception has been successfully modeled in terms of tristimulus values and mapped on the CIE chromaticity diagram.
In short, our eyes see in 2 different ways. It sees black/white thru the rods and since there are much more rods than cones, our eyes are sensitive to changes in amounts of light. The cones see colours and are dominated by the three wavelengths of light red, green and blue.
So we have established 2 things, the eye is sensitive to light and can see a range of colours. But just how many colours can an eye see?
The spectrum of visible light
(Note : These next few sections are excerpt from Color Space Basics from AMIA Conference by Andrew Oran and Vince Roth - www.amiaconference.com/techrev/V12-05/colorspace.htm). I have asked for permission to use these notes and images from the authors but have not obtained approval as yet, should there be any issues, pls report to mod and I can remove if necessary)
Human receptivity to light - or visible light - typically occurs in the range of 390 to 750 nm, or nanometers. Pictured here are one dimensional representations of the visible light spectrum.
CIE 1931 XYZ color space
In 1931 The International Commission on Illumination (abbreviated as CIE for its French name, Commission internationale de l'éclairaget) created one of the first mathematically defined color spaces, the CIE 1931 XYZ color space.
The CIE XYZ color space (aka "the mother of all color spaces") is based on the color sensitivity of the average person as established by testing conducted in the late 1920's, wherein test subjects, using luminance and chroma controls, matched adjustable light to achieve matches to reference colors. The CIE XYZ spectrum locus, pictured above, maps the visible color spectrum along the X and Y axis - chrominance only, not luminance. It's a 2D slice of the full 3D CIE XYZ color space. Around the outside edge of the colored horseshoe are the wavelengths of pure spectral color values expressed in nanometers, with the most saturated colors at the edges, going to white in the center. CIE XYZ is an essential reference tool for color imaging that has been in use since its inception, with only minor revisions over time.
The diagram above represents what the eye can see. There is no manmade equipment that can either capture or show the entire spectrum that the eye can see. The portions below will talk about that. That will start the basis of our calibration topics.
Film…
Movies are typically captured on film.
Film color is typically achieved through a complex series of silver halide grain layers suspended in gelatin; in the case of color negative film, there are three layers of silver halide mixed with color couplers, as well as inter- and protective layers that filter specific light. Together these end up creating unique Yellow, Cyan, and Magenta color layers in the developed negative, and a full color image when reproduced via printing or scanning, akin to the subtractive process outlined above. Because film is subtractive, it's good at creating richly saturated dark colors. It's also an altogether incredible technology however analog it may be, dating back to the 30's with 16mm Kodachrome and the 50's with Eastman Color.
Comparison of color spaces: film color
Film color is not a color space per se. There are limits, or boundaries, to what can be captured on film and reproduced via film print, and these boundaries, when mapped on our handy CIE 1931 XYZ color space chart, establish what we might refer to as film color gamut. As you can see, it's a subset of the larger area: in other words, not all colors within the visual spectrum can be reproduced via a color film capture + display system. The white point - where all colors converge to form white - is noted in the center of the diagram. The complex shape of the film color gamut is a reflection of the fact that film handles color in a non-uniform manner, creating a shifted, non-uniform triangle.
As the diagram shows, film captures less colours than what our eyes can see, so it can never reproduce what we actually saw or even what the director captured on location.
Calibrate/Calibration
Wiki Definition:
Calibration is a comparison between measurements – one of known magnitude or correctness made or set with one device and another measurement made in as similar a way as possible with a second device.
Cambridge Definition:
Describes tools or other devices that are moved slightly or have marks for making accurate measurements
FreeOnline Dictionary Definition
1. To check, adjust, or determine by comparison with a standard (the graduations of a quantitative measuring instrument):
ISO Definition:
Calibration quantifies the relationship between the readings of any meter, weighing balance, mass spectrometer or graduated cylinder and the relevant units in the SI system. Paraphrasing the formal definition in the VIM, the instrument’s readings are compared to the values of a measurement standard under controlled and specified conditions
My Definition:
To compare an instruments performance to a pre-defined standard under a pre-set condition and make changes to the instrument (when possible) to achieve the said standard.
Calibration - The act or process of calibrating or the state of being calibrated
Now that we have the definitions out of the way, we can move on to the next portion of the article.
I would like to talk about an area that I believe is instrumental in Display Calibration.
The study of how film is captured, transformed for theater and then subsequently home cinema.
To understand all this we need to understand our eyes. Our eyes are the windows to the world that we see.
The Eye….
Reference Hecht, 2nd Ed.
Sec. 5.7
The retina contains two types of photoreceptors, rods and cones. The rods are more numerous, some 120 million, and are more sensitive than the cones. However, they are not sensitive to color. The 6 to 7 million cones provide the eye's color sensitivity and they are much more concentrated in the central yellow spot known as the macula. In the center of that region is the " fovea centralis ", a 0.3 mm diameter rod-free area with very thin, densely packed cones.
The experimental evidence suggests that among the cones there are three different types of color reception. Response curves for the three types of cones have been determined. Since the perception of color depends on the firing of these three types of nerve cells, it follows that visible color can be mapped in terms of three numbers called tristimulus values. Color perception has been successfully modeled in terms of tristimulus values and mapped on the CIE chromaticity diagram.
In short, our eyes see in 2 different ways. It sees black/white thru the rods and since there are much more rods than cones, our eyes are sensitive to changes in amounts of light. The cones see colours and are dominated by the three wavelengths of light red, green and blue.
So we have established 2 things, the eye is sensitive to light and can see a range of colours. But just how many colours can an eye see?
The spectrum of visible light
(Note : These next few sections are excerpt from Color Space Basics from AMIA Conference by Andrew Oran and Vince Roth - www.amiaconference.com/techrev/V12-05/colorspace.htm). I have asked for permission to use these notes and images from the authors but have not obtained approval as yet, should there be any issues, pls report to mod and I can remove if necessary)
Human receptivity to light - or visible light - typically occurs in the range of 390 to 750 nm, or nanometers. Pictured here are one dimensional representations of the visible light spectrum.
CIE 1931 XYZ color space
In 1931 The International Commission on Illumination (abbreviated as CIE for its French name, Commission internationale de l'éclairaget) created one of the first mathematically defined color spaces, the CIE 1931 XYZ color space.
The CIE XYZ color space (aka "the mother of all color spaces") is based on the color sensitivity of the average person as established by testing conducted in the late 1920's, wherein test subjects, using luminance and chroma controls, matched adjustable light to achieve matches to reference colors. The CIE XYZ spectrum locus, pictured above, maps the visible color spectrum along the X and Y axis - chrominance only, not luminance. It's a 2D slice of the full 3D CIE XYZ color space. Around the outside edge of the colored horseshoe are the wavelengths of pure spectral color values expressed in nanometers, with the most saturated colors at the edges, going to white in the center. CIE XYZ is an essential reference tool for color imaging that has been in use since its inception, with only minor revisions over time.
The diagram above represents what the eye can see. There is no manmade equipment that can either capture or show the entire spectrum that the eye can see. The portions below will talk about that. That will start the basis of our calibration topics.
Film…
Movies are typically captured on film.
Film color is typically achieved through a complex series of silver halide grain layers suspended in gelatin; in the case of color negative film, there are three layers of silver halide mixed with color couplers, as well as inter- and protective layers that filter specific light. Together these end up creating unique Yellow, Cyan, and Magenta color layers in the developed negative, and a full color image when reproduced via printing or scanning, akin to the subtractive process outlined above. Because film is subtractive, it's good at creating richly saturated dark colors. It's also an altogether incredible technology however analog it may be, dating back to the 30's with 16mm Kodachrome and the 50's with Eastman Color.
Comparison of color spaces: film color
Film color is not a color space per se. There are limits, or boundaries, to what can be captured on film and reproduced via film print, and these boundaries, when mapped on our handy CIE 1931 XYZ color space chart, establish what we might refer to as film color gamut. As you can see, it's a subset of the larger area: in other words, not all colors within the visual spectrum can be reproduced via a color film capture + display system. The white point - where all colors converge to form white - is noted in the center of the diagram. The complex shape of the film color gamut is a reflection of the fact that film handles color in a non-uniform manner, creating a shifted, non-uniform triangle.
As the diagram shows, film captures less colours than what our eyes can see, so it can never reproduce what we actually saw or even what the director captured on location.