Storing Digital Images – Our Sensors Peak Around – 425 Nanometers (Blue) – 550 Nanometers (Green) CSC121, Introduction to Computer – 560 Nanometers (Red) Programming

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Color Images

• the human visual system samples the visible light spectrum Storing Digital Images – our sensors peak around – 425 nanometers (blue) – 550 nanometers (green) CSC121, Introduction to Computer – 560 nanometers (red) Programming

Color Images RGB Color

• We represent color images using composite • most digital photography uses the RGB color color models model employing additive color primaries – separate planes represent specific color channels

pigments light

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RGB Color RGB Color

• has three distinct channels: RED, GREEN, and • We will separate the image to compare the BLUE color channels

each channel is shown as an intensity image to indicate the relative amount that the color contributes to the composite image

RGB Color RGB Color

• We will separate the image to compare the • We will separate the image to compare the color channels color channels

RED CHANNEL GREEN CHANNEL

NOTE: high intensity means high amounts of red; dark means low amounts

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RGB Color CMYK Color

• We will separate the image to compare the • The CYAN-MAGENTA- CYAN color channels YELLOW-BLACK* or CMYK color model is GREEN

used for printing and BLUE based on subtractive BLACK WHITE BLUE CHANNEL primaries YELLOW

MAGENTA

RED *Black is added for print efficiency CMY Color Cube

Color Images Color Images

• the alpha channel is a fourth channel that is • We will be using mostly used as a mask to specify the JPEG images for our transparency/opacity of pixels in the programming composite image • Joint Photographers Expert Group images – baseline: lossy compression algorithm – variable compression rates

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Example Example

Quality = 100, Compression = 2.6:1 Quality = 50, Compression = 15:1 Quality = 25, Compression = 23:1 Quality = 10, Compression = 48:1

Example The If statement

• We have used the If statement in two forms

one-way if (condition): decision statement block

if (condition): two-way statement block-1 decision Quality = 1, Compression = 144:1 else: statement block-2

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Conditional Logic The elif statement

• We can extend the range of choice with Python’s elif

if (condition): statement block-a elif (condition): three-way statement block-b decision else: statement block-c

if statement if-else statement

Conditional Logic Conditional Logic

def choice(): choice = input("Enter your choice: 1 or 2: ") if choice == 1: print "Your choice is 1” elif choice == 2: print "Your choice is 2” else: print "Invalid choice"

if-elif-else statement