1. © 1999 Rochester Institute of Technology Color

2. Imaging Science Workshop for Teachers ©Chester F. Carlson Center for Imaging Science at RIT Color Images u In most cases, we also want to capture color information u The way that we capture, store, view, and print color digital images is based on the way that humans perceive color

3. Imaging Science Workshop for Teachers ©Chester F. Carlson Center for Imaging Science at RIT Color Perception u The eyes have three different kinds of color receptors (‘cones’); one type each for blue, green, and red light. u Color perception is based on how much light is detected by each of the three ‘primary’ cone types (red, green, and blue)

4. Imaging Science Workshop for Teachers ©Chester F. Carlson Center for Imaging Science at RIT Color Perception u Because we have three kinds of cones, every color that we can see can be made up by combining red, green, and blue light - the three “additive primaries”

5. Imaging Science Workshop for Teachers ©Chester F. Carlson Center for Imaging Science at RIT Additive Color Mixing: u Mixing the three additive primaries together is known as “additive mixing” to distinguish it from mixing paints or dyes (“subtractive mixing”)

6. Imaging Science Workshop for Teachers ©Chester F. Carlson Center for Imaging Science at RIT Additive Color Mixing: u Remember that we are discussing “additive color mixing.” The mixing happens in the visual system, not on the screen. u You can verify this by examining a TV or computer screen at high magnification. Color monitors and LCD displays only make red, green, and blue light. All other colors are synthesized in the visual system.

7. Imaging Science Workshop for Teachers ©Chester F. Carlson Center for Imaging Science at RIT Additive Color Mixing: u By recording and playing back the amount of Red, Green, and Blue at each pixel, a digital camera can capture the colors in a scene.

8. Imaging Science Workshop for Teachers ©Chester F. Carlson Center for Imaging Science at RIT RGB Color Images u Each one of the color images (‘planes’) is like a grayscale image, but is displayed in R, G, or B = u The most straightforward way to capture a color image is to capture three images; one to record how much red is at each point, another for the green, and a third for the blue.

9. Imaging Science Workshop for Teachers ©Chester F. Carlson Center for Imaging Science at RIT RGB Color Images u To capture a color image we record how much red, green, and blue light there is at each pixel. u To view the image, we use a display (monitor or print) to reproduce the color mixture we captured. Q) How many different colors can a display produce? A) It depends on how many bits per pixel we’ve got. For a system with 8 bits/pixel in each of the red, green, and blue (a ‘24-bit image’):

10. Imaging Science Workshop for Teachers ©Chester F. Carlson Center for Imaging Science at RIT RGB Color Images: 24-bit color u Every pixel in each of the three 8-bit color planes can have 256 different values (0-255) u If we start with just the blue image plane, we can make 256 different “colors of blue” 0 255

11. Imaging Science Workshop for Teachers ©Chester F. Carlson Center for Imaging Science at RIT RGB Color Images: 24-bit color u Every pixel in each of the three 8-bit color planes can have 256 different values (0-255) u If we start with just the blue image plane, we can make 256 different “colors of blue” u If we add red (which alone gives us 256 different reds): 0255 0

12. Imaging Science Workshop for Teachers ©Chester F. Carlson Center for Imaging Science at RIT RGB Color Images: 24-bit color u Every pixel in each of the three 8-bit color planes can have 256 different values (0-255) u If we start with just the blue image plane, we can make 256 different “colors of blue” u If we add red (which alone gives us 256 different reds): u We can make 256 x 256 = 65,536 combination colors because for every one of the 256 reds, we can have 256 blues. 0255 0

13. Imaging Science Workshop for Teachers ©Chester F. Carlson Center for Imaging Science at RIT RGB Color Images: 24-bit color for each one u When we have all three colors together, there are 256 possible values of green for each one of the 65,536 combinations of red and blue: u 256 x 256 x 256 = 16,777,216 (“> 16.7 million colors”)

14. Imaging Science Workshop for Teachers ©Chester F. Carlson Center for Imaging Science at RIT RGB Color Images: 24-bit color u The numbers stored for each pixel in a color image contain the color of that pixel

15. Imaging Science Workshop for Teachers ©Chester F. Carlson Center for Imaging Science at RIT Color Image = Red + Green + Blue = u In a 24-bit image, each pixel has R, G, & B values u When viewed on a color display, the three images are combined to make the color image. 212 100 139196 163 75 113149 37 44 6372 95 118 155170 189 162 38 41 60 8278 182 161 50 43 57 6863