CSC 1040 - Computing with Images Image encodings CSC 1040 CSC 1040 - Computing with Images

CSC 1040 - Computing with Images What’s a picture? We have seen that programs represent pictures as grids of picture elements or pixels Stephanos with his eraser collection CSC 1040 - Computing with Images

CSC 1040 - Computing with Images Pixel encodings RGB Color 3 colors: red, green, blue 8 bits/color 24 bits Bitmap 1 bit Grayscale 8 bits CSC 1040 - Computing with Images

Additive color model: RGB In RGB, a color has three component: R: Amount of redness G: Amount of greenness B: Amount of blueness These values are usually represented by numbers in the range 0…255 Additive color model: Based on the way the light mixes on a computer screen. It is called an additive color model because if you add the three primaries (red, green and blue) together, you get pure white light. CSC 1040 - Computing with Images

Subtractive color model: CYM In CYM, a color has three component: C: Amount of cyan Y: Amount of yellow M: Amount of magenta Usually numbers in the range 0…255 Subtractive color model: CMY is based on the way translucent inks combine to block light – thus “subtracting” light. In reality you need to add pure black ink (“K”) to get real black – therefore CYMK CSC 1040 - Computing with Images

CSC 1040 - Computing with Images Encoding RGB Each component color (red, green, and blue) is encoded as a single byte Colors go from (0,0,0) to (255,255,255) If all three components are the same, the color is in greyscale (50,50,50) at (2,2) (0,0,0) (at position (1,2) in example) is black (255,255,255) is white CSC 1040 - Computing with Images

CSC 1040 - Computing with Images red=108 green=86 blue=142 y = 9 Color:(108,86,142) Position: (12,9) x = 12 CSC 1040 - Computing with Images

Additive/Subtractive Color We choose 3 primary colors that can be combined to produce most (but NOT all) the visible colors: Additive primaries (Combining light): Subtractive primaries (combining ink, thus subtracting light): Cyan Yellow Magenta Red Green Blue CSC 1040 - Computing with Images

Let’s practice making these colors in Photoshop Additive primaries Start with white background, Start with black background, use a hard edged brush of large diameter and set mode to “Darken” use a hard edged brush of large diameter and set mode to “Lighten” Apply cyan, yellow, magenta Apply red, green, blue Subtractive primaries CSC 1040 - Computing with Images

Dimensions of color CSC 1040 - Computing with Images Source: http://www.huevaluechroma.com/012.php CSC 1040 - Computing with Images

Color in the eye: What does one million colors look like? This image (when viewed in full size, 1000 pixels wide) contains 1 million pixels, each of a different color. The human eye can distinguish about 10 million different colors. Source: Wikipedia commons CSC 1040 - Computing with Images

The color gamut Not all visible colors can be produced by any 3 primaries! The color gamut refers to the range of colors for a particular color system Source: http://dx.aip.org/advisor/cmyk_color.html CSC 1040 - Computing with Images