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Chapter03

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Chapter03

  1. 1. Ch 3: Digital Imaging Fundamentals Photoshop CS6 Essentials By Scott Onstott
  2. 2. Ch 3: Digital Imaging Fundamentals Benefits of More Megapixels • Larger DSLR sensors capture millions more pixels (megapixels) compared to point-and-shoot cameras • More megapixels means you have more detail and less noise • You can digitally zoom in to large images and the details remain crisp • More megapixels also means more data, larger file sizes, and more RAM required
  3. 3. Ch 3: Digital Imaging Fundamentals Pixel Aspect Ratio • Pixels can have non-square aspect ratios • Use square pixels for print and for the Web • Video clips often use non-square pixels • You can change the pixel aspect ratio using the View menu and in the File > New dialog box
  4. 4. Ch 3: Digital Imaging Fundamentals Aliasing and Anti-Aliasing • Aliasing is the stair-stepping artifact that occurs in grids of pixels • Lines are not aliased when you draw them horizontally, vertically, or at 45 degree angles • Off-angled lines exhibit aliasing which can be reduced by dithering the edge (blue line at right) with intermediate values • Anti-aliased edges appear blurry compared to aliased edges but the stair-stepping is removed
  5. 5. Ch 3: Digital Imaging Fundamentals Primary Colors • Red, Green, and Blue are the primary additive colors • Cyan, Magenta, and Yellow are the primaries of subtractive colors • CMY are secondary colors in the RGB system • RGB are secondary colors in the CMY system • Black (abbreviated as K) is added to the subtractive system, making CMYK the 4- colors used in offset printing
  6. 6. Ch 3: Digital Imaging Fundamentals Color Channels • Color is split into primary components such as Red, Green, and Blue • Primary color components are stored in grayscale image channels • Color is reconstituted by illuminating red, green, and blue sub-pixels in your monitor with varying intensities according to the luminance values in the corresponding color channels Photo courtesy of iStockphoto, ©Neustockimages, Image #7007990
  7. 7. Ch 3: Digital Imaging Fundamentals Alpha Channels • Alphas are additional channels • Alpha 1 is used to store transparency information • When the Alpha 1 channel is displayed against the RGB channels a red rubylith overlay appears to indicate areas of transparency • Not all formats support alpha channels • TIF and TGA do support alphas Photo courtesy of iStockphoto, ©Neustockimages, Image #7007990
  8. 8. Ch 3: Digital Imaging Fundamentals Understanding Lab Color • L* a* b* stands for Lightness, a, and b channels • Detail is carried in the Lightness channel • Color is carried using a combination of a and b channels • Lab color is a convenient mode that isolates image detail (can be used for sharpening or grayscale conversion) Photo courtesy of iStockphoto, ©Terry J Alcorn, Image #14990625
  9. 9. Ch 3: Digital Imaging Fundamentals Grayscale vs. Bitmap Modes • Grayscale images have a range of tonal values in a single channel (256 gradations in 8-bit) • Bitmap images also employ a single channel • Bitmap images are the most primitive images having only black and white pixels without any intermediate shades of gray • Bitmap images can be dithered or processed with a halftone screen Photo courtesy of iStockphoto, ©Terry J Alcorn, Image #14990625
  10. 10. Ch 3: Digital Imaging Fundamentals Understanding Histograms • Histograms help you see how well the dynamic range is being utilized • Histograms are made of black vertical bars representing how many pixels are in the shadows, mid-tones, and highlights • Blank areas at the edges of a histogram show there are values (blackest blacks or whitest whites) that aren’t being used • Gaps or spikes in a histogram show that information has been “destroyed” by being pushed beyond certain mathematical limits

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