Color mixing is created by an artist.
Shades, tints and tones in scene can be produced by mixing color pigments (hues) with white and black pigments.
Shades:
Add black pigment to pure color.
The more black is the pigment, to darker the shade.
Tints:
Add white pigment to the original color.
Made lighter by adding more white.
Tones:
Produced by adding both black and white pigments.
4.6.1 RGB colour model
RGB Color model
In-this model the three primitives red, green and blue are used.
These visual pigments have a peak sensitivity at wavelengths of about 630 nm for red, 530 nm (green) and 450 nm for blue.
We can represent this model with the unit cube defined as RGB axes.
The origin represents black and the vertex with co-ordinates (1, 1, 1) is white.
→ Each color point within the bounds of the cube can be represented as the triple (R, G, B) where values for R,G and B are assigned in the range from 0 to 1.
→ The color Cλ is expressed in RGB component as
Cλ = RR + GG + B.
→ The magenta vertex is obtained by adding red and blue. The yellow vertex is obtained by adding green and red and so on.
4.6.2 YIQ colour model
YIQ is the color space used by the NTSC color TV system employed mainly in north and central America and Japan.
I stands for in-phase, while Q stands for quadrature referring to the components used in quadrature amplitude modulation.
Some forms of NTSC now use the YUV color space, which is also used by other systems such as pal. The Y component represents the luma information and is the only component used by black-and-white television receivers.
I and Q represent the chrominance information. In YUV, the U and V components can be thought of as X and Y coordinates within the color space.
I and Q can be thought of as a second pair of axes on the same graph, rotated 33°. Therefore IQ and UV represent different coordinate systems on the same plane.
The YIQ system is intended to take advantage of human color-response characteristics.
The eye is more sensitive to changes in the orange-blue (I) range than in the purple-green range (Q) — therefore less bandwidth is required for Q than for I.
Broadcast NTSC limits I to 1.3 MHz and Q to 0.4 MHz. I and Q are frequency interleaved into the 4 MHz Y signal which keeps the bandwidth of the overall signal down to 4.2 MHz.
In YUV systems, since U and V both contain information in the orange-blue range, both components must be given the same amount of bandwidth as to achieve similar color fidelity.
Very few television sets perform true I and Q decoding due to the high costs of implementation.
Compared to the cheaper R-Y and B-Y decoding which requires only one filter, I and Q each requires a different filter to satisfy the bandwidth differences between I and Q.
These bandwidth differences also requires that the 'I' filter include a time delay to match the longer delay of the 'Q' filter.
The Rockwell Modular Digital Radio (MDR) was one I and Q decoding set, which in 1997 could operate in frame at a time mode with a PC or in real time with the Fast IQ Processor (FIQP).
Some RCA "colortrak" home TV receivers made circa 1985 not only used I/Q decoding, but also advertised its benefits along with its comb filtering benefits as full "100 percent processing" to deliver more of the original color picture content.
Earlier more than one brand of color TV (RCA, Arvin) used I/Q decoding on models utilizing screens about 13 inches (measured diagonally).
The original Advent projection television used I/Q decoding. Around 1990 at least one manufacturer (Ikegami) of professional studio picture monitors advertised I/Q decoding.
4.6.3 CMY colour model
It is possible to achieve a large range of colors seen by humans by combining cyan, magenta and yellow transparent dyes/inks on a white substrate.
These are the subtractive primary colours.
Often a fourth ink, black is added to improve reproduction of some dark colors. This is called "CMY" or "CMYK" color space.
The cyan ink absorbs red light but transmits green and blue.
The magenta ink absorbs green light but transmits red and blue and the yellow ink absorbs blue light but transmits red and green.
The white substrate reflects the transmitted light back to the viewer.
Because in practice the CMY inks suitable for printing also reflect a little bit of color making a deep and neutral black impossible, the K (black ink) component, usually printed last is needed to compensate for their deficiencies.
Use of a separate black ink is also economically driven when a lot of black content is expected, e.g. in text media, to reduce simultaneous use of the three colored inks.
The dyes used in traditional color photographic prints and slides are much more perfectly transparent, so a K component is normally not needed or used in those media.
4.6.4 HSV colour model
→ To give a color specification, a user selects a spectral color and the amounts of white and black that are to be added to obtain different shades, tints and tones.
→ Color parameters are hue (H), saturation (S) and value (V).
HSV Model:
HSV model
→ Viewing the cube along the diagonal from the white vertex to the origin, the outline of the cube has the hexagon shape.
→ The boundary of the hexagon represents the various hues and it is used as the hop of the HSV hexacone.
→ In hexcone, saturation is measured along a horizontal axis and value is along a vertical axis through the center of the hexcone.
For Adding Black:
H = 2 and 0
V = 0.4
S = 1
Where V → decrease.
S → same.
Adding White:
S = 0.3
V = 6
H = 0
Where S → decrease.
V → same.
4.6.5 HLS colour model
HLS Color Model
This model (Hue, Lightness, and Saturation) was popularized by Tektronix who used it to define the color effects on its monitors.
The hues are specifies by angles, as they were for HSV, but in this model Blue is at 0°, Magenta is at 60°, Red is at 120°, Yellow is at 180°, Green is at 240°, and Cyan is at 300°.
So the order on which the colors appear is the same as before and complementary colors are still on opposite sides of the circle separated by 180°, but the color sequence begins with blue instead of red.
The angle is measured from above as before beginning at the line shown from medium gray to blue. The hue definitions now lie on a circle, as compared to the hexagon that was used for HSV.
This is much easier to deal with since full saturation of any hue will now have an S value of 1.0, as compared to the 2. 3 that we had to use for the S value for orange using HSV.
Once again, gray scales appear on the center line of symmetry with L = 0 at the bottom and L = 1 at the top. In this model the line is twice as long as in HSV.
White, Black, Magenta, Blue, Red, Green, Cyan, Yellow, Gray scale Pure colors have an L value of 0.5. So, for example, pure orange is at an HLS triple of (150°, 0.5, 1.0).
Overall HSV seems to be the preferred method for interactive selection of colors.
4.7 Colour selection
Color systems
There are various types of color systems that classify color and analyze their effects. The American Munsell color system devised by Albert H. Munsell is a famous classification that organizes various colors into a color solid based on hue, saturation and value.
Other important color systems include the Swedish natural color system (NCS) from the scandinavian color institute, the optical society of America uniform color space (OSA-UCS), and the Hungarian coloroid system developed by the Budapest university of technology and economics.
Of those, the NCS is based on the opponent process color model, while the Munsell, the OSA-UCS and the Coloroid attempt to model color uniformity.
The American Pantone and the German RAL commercial color-matching systems differ from the previous ones in that their color spaces are not based on an underlying color model.
Color system