Theory of colors
| Adiseshanaik |
Meaning of some terms
* ICC Profile: International Color Consortium Profile
* CMYK: Cyan Magenta Yellow and Key
* PCS: Profile Connection Space
* sRBG: standard Red Blue Green
* HSV: Hue Saturation and Brightness (related to color space)
* CIE: International Commission on Illumination
* CRI: Color Rendering Index (characteristcs of a light source reproducing the colors
of any subject accurately comparing those from an ideal natural light source)
* CCT: Correlated Color Temperature
* Color Temperature: When a black body is heated at "X" temperature (measured in Kelvin),
the black body radiates a color which matches the color of a light source. Then, X is referred
as the color temperature of that particular light source. Black body is the one which absorbs
everything without allowing any radiation to pass through it. In this context, Blue is the hottest
color and Red is the coolest one (quite reverse to what we follow in our daily life).
The day light (5600K) has a color profile almost similar to that of a black body radiation.
The colour varies from Blue to Red depending upon the position. This change in colour is
due to refraction and scattering effect. This property is not having any relationship with
black body radiation but approximated for photography and other purposes. In digital photography
color temperature matching for the monitor is important and can be done using monitor
calibration (color matching) softwares.
* Color Balance: This is different from Color temperature. In Color temperature, there is only
one parameter i.e the color at different temperature. Color balance is all about bringing the
neutral colours correctly by adjusting the amount of primary colors (RGB). In a photo which is
not color balanced, we find some color cast. To get the right color balance, both exposure and
the amount of primary colors are important. If an image is shot in JPEG mode, it is always better
to get the colour balance right out off the camera. If one needs to adjust manually, RAW is very
handy. This happens because of some difference between the capturing device (Camera)and the viewing
device (monitor). In film cameras, this is done with filters attached to the lens
* Color Space: In a 3-dimensional system, if each axis represents one primary color, then the
total space is called the "Color Space" of those primary colors. But, there are color spaces
with more and even less dimensions.
The HSV color space uses Hue, saturation and brightness. For having any color spaces, the standard
is dervided from CIE 1931 (XYZ) color space. This has definitions to all the colours which
can be seen from a normal human eye.
sRGB color space was originally designed for monitors and TV systems. This uses Red, Green and
Blue as three primary colors. The gamut (set of colors) of this color space is lesser
but well defined. This color space is almost considered as the standard system for internet usage.
"CIE Lab" is one more color space used as basic space which defines all colors visible to the
human eye and is independent of any device. "L a b" constitute the coordinates for this color
space. The three coordinates represent Lightness, its position between "red/magenta & green" and
its position between "yellow & blue". The "L" component is accurate to the perception of human
eye to lightness. One can get perfect color balance in adjusting the "a" and "b" components and
even through lightness contrast adjustment. The set of colors (Gamut) in Lab color space is
very huge. The gamut of human eye is very much less compared to Lab space. So, images which are
edited using Lab color space have some imaginary colors which are to be corrected properly to the
nearest human eye gamut.
CMYK color space is used in printers. Here, the black color is used exclusively to have perfect
black as the primary colors (cyan, magenta, yello) won't produce perfect black in this
color space. The gamuts for RGB and CMYK are totally device dependent and are different from
each other.
Adobe RGB developed by Adobe system covers almost 50% of CIELab gamut and has more gamut than the
sRGB color space. This also uses Red Green and Blue as primary colors but in the form of triplets.
|
|
|
|
