Terminology
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Absolute Colormetric Intent
 
- The same Color Intent as Relative colormetric
except that the out of gamut color shifts do not affect the white point.
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Additive Color
 
- Adding RGB colors: R+G=Y, G+B=C, R+B=M, R+G+B=White
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AdobeRGB98 Color Space
 
- The sRGB Color Space redefined with
RGB ranging from 0.0-1.0 with a Gamma
of 2.2. It expands the sRGB Color Space mostly in the Cyan to Green region.
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Anti-Aliasing Filter
 
- An optical filter, which is located in front of the camera's image sensor and
Bayer-Filter which slightly blurs the optical image
to reduce pixel quantization distortion of high-contrast image edges. While
this filter does add distortion, the digital image gives a more visually
pleasing result.
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Bayer-Filter
 
- The RGGB color filter in a digital camera located between the anti-aliasing
optical filter and the image sensor. This filter desults in individual pixel
sensors responding to Red Green and Blue light. Because of the human eye's extra
sensitivity to Green light, there are two Green filtered pixels for every Red
and Blue filtered pixels -- thus RGGB.
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Chroma
 
- The Munsell Color System's reference to
Saturation
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CIE XYZ Color Space
 
- An RGB component Color Space derived from the RGB
human eye Tristimulus perception of color
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CMYK
 
- A color description based on subtractive values of Cyan, Magenta, Yellow
and Black (i.e. printer ink). White(no ink), Cyan, Magenta, Yellow,
Blue(cyan + magenta), Green(green or cyan + yellow), Red(red or magenta + yellow),
Brown(cyan + magenta + yellow), Black.
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Color Intent
 
- The translation of image file colors to the Color Space Gamut of an output
device -- usually a photo-printer. Intent types are:
Relative Colormetric,
Perceptual,
Absolute Colormetric and
Saturation.
-
Color Lightness
 
- Color Tone or Color Value
-
Color Tolerance
 
- The range of Hues, of constant Lightness,
within a minimal perception of difference to a reference color
-
Color Tone
 
- Human perception of color brightness
-
Color Sensitivity
 
- Sensor - the number of distinguishable colors up to the sensor noise level
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Color Space
 
- The available numeric range of colors which defines the working space of a
device or software application
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Color Value
 
- Color Tone
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Cone Cells
 
- The Retinal cells of the eye, grouped by 3, which are sensitive to the RGB
colors. Red (560-580nm peak), Green (530-540nm peak) and Blue (420-440nm peak).
Cone cells require more light than Rod Cells which is why colors fade
as it gets dark.
-
Demosaicing
 
- The root term is 'mosaic' which is a group of colored tiles which combine to show an
image. The inverse process, 'de-mosaic' if you will, of combining the RGGB
Bayer-Filter digital camera image sensor pixel information to
calculate the per-pixel RGB data generated to construct the JPEG image file as the
output from the camera.
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D65
 
- The acronym for the default Color Temperature
of Daylignt at 6500-degK
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DPI
 
- Dots Per Inch - The printer's ink droplet density - droplet volume is
usually measured in picoliters
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DPP
 
- Dots Per Pixel - The printer's ink droplet density per image pixel area. It
can be calculated as DPI/PPI = DPP .
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Gamma
 
- The non-linear adjustment to the 1:1 ratio between RGB values and output
Luminance
-
Gamut
 
- The range of color Hues achievable within a
Color Space
-
Granger Chart
 
- A test image space with Left-Right color spectrum gradient and Top-Bottom
luminocity gradient.
Combined, they provide the full mathematical range of color values -- even
though not all can be accurately displayed or printed.
-
GreyBalanceCard
 
- Used for setting white balance. not exposure.
A printed Neutral Grey surface which provides a more
reflective surface than grey exposure cards to make the camera's AWB or CWB
task easier. A grey surface avoids the issues of "white" surfaces which generally
provide a slight red or blue color cast because "pure white" is difficult to
achieve.
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12% Grey
 
- Used for setting exposure, generally not white balance.
A printed Neutral Grey surface which provides ~41%
reflectance (L*=0.41, a=0, b=0) of the incident light and reflects Red, Green and Blue equally. This
reflectance level correlates with 1/2 stop lighter and best matches the mid-EV sensitivity point of digital
camera silicon-based sensors.
-
18% Grey
 
- Used for setting exposure, generally not white balance.
A printed Neutral Grey surface which provides ~50%
reflectance (L*=0.5, a=0, b=0) of the incident light and reflects Red, Green and Blue equally. This
reflectance appears roughly midway between black and white to the human eye and is thought to
best matche the 'mid-tone' reflectance of B&W prints from the Kodak
film era as promoted by Ansel Adams.
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HSL
 
- A ColorSpace defined by Hue,
Saturation and Luminance
-
Hue
 
- A color value; usually described by RGB, CMYK,
which appears most dominant in the spectrum presented to the eye - which may not
be the peak frequency of that spectrum. A Hue is independent
of Saturation
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Image Clarity
 
- For digital images, it is generally about half the
Image Resolution because of the Anti-Aliasing
and Bayer Filters plus this camera-internal
Demosaising which processes the RAW
RGGB sensor pixel data to produce JPEG
image files.
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Image Resolution
 
- For digital images, it is the number of pixels which defines
an image. It is often described by image pixel dimensions; eg. 2592 x 3888 for the
Canon 40D. It is generally not represenative of Image Clarity
which is a measure of human visual detection of image detail.
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JPEG
 
- Joint Photographics Group lossy image compression standard image encoding. It
works best on 'natural' images because it uses lossy compression where image
errors will be less noticable. The advantage is significatly smaller files
which look quite close to the original detail. RAW
images from digital cameras do not suffer from these compression artifacts.
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La*b* Color Space
 
- Lightness + a* and b* color-opponants which are
derived from the XYZ Color Space
-
Lightness
 
- Luminance. Sometimes used in HSL references.
-
Light Temperature
 
- The temperature, in degrees-Kelvin, of the source emitting the light. Incandescent
light spectra are centered at 2854-degK and daylight is centered at 6500-degK.
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LPI
 
- Lines Per Inch - The closest spacing of parallel lines, usually printed, which
are visually distinct from each other.
-
Luminance
 
- The color density or Luminosity per unit area (candela per sq-meter)
-
Luminosity
 
- The measure of absolute color brightness; often mistakenly used for Luminance
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MacAdams Plot
 
- An overlay plot of elliptical areas plotted around specific colors of a standard
CIE
color gamut plot. The elliptical areas represent the range of color values, relative to
a single color value (the center) which have no human detectable color difference.
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Metamerism
 
- The change in perceived reflected color as a result of the light source temperature
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Munsell Color System
 
- A Color Space based on Hue, Lightness
and Chroma
-
Neutral Grey
 
- A color which is formed from equal intensities of Red, Green and Blue such that the
human eye perceives no color tint toward any of those primary colors.
See 12% Grey
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Perceptual Intent
 
- The Color Intent where all image colors are linearly
ratioed to make them fill the color gamut of the output device -- usually a printer.
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Pixel
 
- For digital images, it is smallest, square unit of measure for an image area.
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PPI
 
- Pixels Per Inch - The density of pixels per unit inch in an image print
-
Print Color Quantization Error
 
- The print color resolution error resulting from dot diffusion limitations for
color mixing with high (>200) print ppi settings. As print pixel size diminishes,
there are fewer ink dots to describe a mixed-ink color. This error can be over 20%
at 400 ppi on a Canon 8-ink Pro9000.
-
ProPhoto RGB Color Space
 
- A 16-bit Color Space defined for Adobe Camera Raw software
for processing RAW digital camera .DNG images
-
RAW
 
- Camera-specific non Demosaised,
Bayer-Filtered linear image sensor data file
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Relative Colormetric Intent
 
- The Color Intent where all in-gamut colors remain
unchanged but out of gamut colors are all mapped to the nearest gamut color.
-
Resolution
 
- For digital images, it is the number of pixels which can be
detected or described within an image.
-
RGB [sRGB]
 
- A color description based on the additive values of pure Red, Green and
Blue color light (i.e. those displayed on a color monitor). Usually the
Color Values are quantified as 8-bit (0-255) for a
total of 24-bit color resolution.
-
RGGB [sRGB]
 
- A reference to the Bayer-Filter's effect of causing
the camera sensor to produce RAW image data in a color pattern
of 1-Red, 2-Green and 1-Blue pixel for each 2x2 group of pixels. The Green data
appears twice as often because the human eye is more sensitive to Green.
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Rod Cells
 
- The Retinal cells of the eye, sensitive only to light intensity which are
broadly centered about the Cyan wavelength (490-495nm) and which provide
visual perception for intensities below that necessary to perceive color.
The majority of Cone Cells are tightly packed in
the Fovae which is the area of the retina directly opposite the lens.
The Fovae is responsible for sharp focus and thus human visual acuity.
50% of the cells of the optic nerve bundle are dedicated to Fovael cells.
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Saturation
 
- The measure of a color's purity - a more narrow spectrum is a more pure
Hue and is thus higher Saturation
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Saturated Intent
 
- The Color Intent where color is shifted to
maximize saturation and minimize color dithering
at the expense of Hue and Lightness.
-
sRGB Color Space
 
- The Color Space composed of [RGB] tuples, each
having 8-bit resolution (numeric value of 0 to 255);
Gamma of 1.0
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Subtracive Color
 
- Mixing CMYK colors: C+M=B, M+Y=R, C+Y=G, C+M+Y=Black
(dark dark brown); K=Black
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Tristimulus Values
 
- The three RGB color values, as a group, which define human perception of
any specific color
-
Vernier Acuity
 
-The ability to visually align two line segments (0.13 arc-min)
-
Visual Acuity
 
- The measure of the spatial resolution of the visual processing system under
optimal conditions (0.6 arc-min is typical for the human eye)
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White-Balance
 
- The process of correcting a digital camera RGB sensitivity relative to the color
temperture of the source light such that the subjects in photographs will have a
more natural color balance. The process can be automatic (AWB) or can be custom (CWB)
by using a neutral-grey surface as a source of reflected light.
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