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COSC 109 Ch.3 Notes.doc

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Computer Science
COSC 109
Mona Tavakalon

COSC 109 Chapter 3: Capturing and Editing Digital Images There are 4 different types of scanner: • Flatbed • Sheet-fed • Handheld • Drum There are 3 different types of scanner resolutions: • Optical • Enhanced • Reported in dpi (Dots Per Inch) How Scanners work: • Flatbed scanners have a moving scan head that has a row of light sensors.As the sensors move forward they map every pixel. • The scan head moves across the scanner bed during scanning which is powered by a stepper motor. • When the light sensors scan an image each sensor produces a sample, which is a color value which corresponds to the a specific location on the image. Each sample (color value) is a pixel. When scanning you also need a sampling rate: • Sampling in x-direction: number of sensors available in the row • Sampling in y-direction: discrete stepwise movement of the scan head When you are determining scanning resolution you need to think about how the scanned image is going to be used. Is it going to be printed or web/ on screen display? • Print - physical dimensions of the image - requirement of the printing device (resolution) • Web or on-screen display -pixel dimensions of the image With digital cameras you just point and shoot and it captures the image. • D-SLR (digital single-lens reflex) -Most D-SLR cameras use interchangeable-lenses • There are 2 digital camera sensors -CCD (charge coupled device) -CMOS (complementary metal-oxide semiconductor) • The size of the sensor and the number of light-sensing sites determine the maximum resolution of the digital camera. • Camera resolution is by Megapixels Ex. 1 megapixel = 1,000,000 pixels An image of 3000 × 2000 pixels has a total number of pixels of: 3000 × 2000 pixels = 6,000,000 pixels = 6,000,000 pixels/1,000,000 pixels/megapixel = 6 megapixels • Megapixels do not provide information about the aspect ration of an image (relative width and height of image) • Digital photo quality is determined by -the optics of the lens -the size and quality of the sensor -the cameras electronics -the cameras image processing software • When printing an image the print size depends on the printing resolution Ex.A6MP image: 3000 x 2000 pixels A2MP image: 1600 x 1200 pixels The print size of a 6mp image: -Printed at 150 ppi (pixels per inch) 3000pixels / 150ppi= 20” The print size of a 2MP image: -printed at 150ppi (pixels per inch) 1600pixels/150ppi =10.7” • Images with the same printing resolution and more MegaPixels have bigger prints • Images with different printing resolution have different printing sizes There are a few basic steps to retouching a digital image 1. Crop and straighten -If you only want a certain part of the picture or if the image is tilted. -Photoshop tool: Crop Tool 2. Repair small imperfection -There could be a pimple and you want to get rid of it -Photoshop tool: Clone stamp or Healing brush 3. Adjust the overall contrast or tonal range of image -If you want to maximize the to
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