Images & Computer Graphics: Color Models & Vector vs Raster

Explanation

Digital images are two-dimensional matrices of color values f(x, y). In 24-bit True Color raster graphics, each pixel allocates 8 bits each to Red, Green, and Blue (16.7 million colors). Because the human visual system is far more sensitive to spatial luminance variations than color nuances, broadcast and digital video systems convert RGB into YCbCr and discard color details through chroma subsampling (e.g., 4:2:0 halves both horizontal and vertical color resolution without noticeable visual degradation).

Key points

• Vector Graphics: Geometric primitives (points, lines, Bézier curves, polygons) defined mathematically; infinitely scalable without quality loss; formats: SVG, EPS.
• Color Perception: Human eye contains rod cells (luminance) and cone cells sensitive to Red, Green, and Blue wavelengths.
• Color Models: Additive RGB (monitors/displays), Subtractive CMYK (printing/dyes), and Human-perceptual HSL/HSV (Hue, Saturation, Value/Lightness).
• YUV / YCbCr Color Spaces: Separates Luminance (Y - brightness) from Chrominance (U/Cb, V/Cr - color); exploits human eye's higher sensitivity to brightness to achieve chroma subsampling (4:2:2, 4:2:0).

Example

Code examples

/*
RGB to YCbCr Conversion Matrix (ITU-R BT.601):
Y  =  0.299 * R + 0.587 * G + 0.114 * B
Cb = -0.169 * R - 0.331 * G + 0.500 * B + 128
Cr =  0.500 * R - 0.419 * G - 0.081 * B + 128
*/

Exam questions

• [8 Marks] Differentiate between Raster Graphics and Vector Graphics with respect to resolution, file size, scaling, and application domains.
• [7 Marks] Explain the RGB, CMYK, and YUV/YCbCr color models. What is Chroma Subsampling (4:4:4, 4:2:2, 4:2:0) and why is it used?