Digital Image Basics

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This is the introductory slideshow for our "Digiatl Image Basics" faculty workshop at OIT Academic Computing, UMass Amherst.

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Digital Image Basics

  1. 1. An Introduction to Digital Images Michele Turre June 2009 Academic Computing Office of Information Technologies University of Massachusetts Amherst
  2. 2. Getting images… • Flatbed scanner • Search the Web Google, Flickr, Creative Commons • Film scanner • Online Collections • Digital camera Public: loc.gov, NASA, museums Library: ArtStor, Luna Insight • Computer drawings Commercial: Corbis, Getty Images, etc.
  3. 3. Fair Use for teaching & research Can you use it ? 1. Purpose for which you are using the work. 2. Natureof copyrighted work (phone directory vs creative expression). 3. Portionof work you intend to reproduce (small portion vs entirety). 4. Effect of your use on potential market, number of copies you make. Copyright:Monday, June 15th (11:00 a.m. - Noon) Finding Copyright-Free Media: Monday, June 15th (1:00 - 2:00 p.m.)
  4. 4. Technical background • What is a pixel-based image? • What is resolution? • What do I need to know about color?
  5. 5. Two types of digital images: BITMAP IMAGES VECTOR GRAPHICS camera captures & scans computer drawings
  6. 6. Two types of digital images: BITMAP VECTOR Scan of a pencil Drawing made in photograph drawing PowerPoint
  7. 7. A bitmap image is like a mosaic crossed with paint-by-numbers
  8. 8. Each picture element (or ―pixel‖) has a numerical color value 255.204.153
  9. 9. Resolution: pixels per inch (ppi) 1 inch 33 ppi 11 ppi 80 K 5K more pixels in an inch fewer pixels in an inch = = more detail, bigger files less detail, smaller files
  10. 10. Pixel-based images should only be made smaller, enlarging just makes them blurry
  11. 11. Vector images can be scaled, no problems! Same drawing, same file size (4 K) — whether rendered large or small looks the same.
  12. 12. Color Depth: Number of colors in image— less colors, smaller file size 16 million colors 8 colors 256 shades of gray 212 k 12 k 65 k
  13. 13. Use the right number of colors for the image, and no more than needed photograph Solid-colored graphic Needs millions of colors Needs only 3 colors
  14. 14. Downloading images from Online Collections Look for images with enough pixel resolution for your use. Sometimes you have a choice to download different sizes…
  15. 15. Formatting images for different uses… • Web • PowerPoint • Print
  16. 16. SCANNING? Start from a high quality scan. Create new files from the scan for different purposes. Web site PowerPoint Original scan (See page 7 of handout for scanning tips)
  17. 17. USING A DIGITAL CAMERA? Backup your camera files. Save new files for each purpose. Web site PowerPoint Original 10 MP camera file (See page 7 of handout for scanning tips)
  18. 18. Some software will resize pictures for you… • Camera software, Vista Photo Gallery, MS Picture Manager, Apple iPhoto or Apple Preview Look for … Email this picture Export for Web • Web apps such as Flickror Facebook resize pictures for you. - Upload full sized file - A smaller, resized version is sent tovisitor’s browsers
  19. 19. HANDS-ON… Locate a large image (at least 5 Megabytes). We will show you how to… 1. Open in Photoshop 2. Crop 3. Adjust color 4. Resize for different uses
  20. 20. Formatting images for the Web Original scan Cropped & sized down for Web page 1. Resize (shrink) in Photoshop or another application. 2. • Save photos as JPEG (lowest possible quality). • Save line art as GIF (fewest possible colors). 3. • For Web apps (e.g., Blogs or SPARK), upload resized image • Dreamweaver or other HTML editor: Upload both image file and HTML file to the Web server.
  21. 21. Sizing an image to fit on a Web page Most Web pages are about 780 pixels wide. Layout columns are narrower. Resize images accordingly… . Original scan at screen resolution Cropped &sized-down 2100 x 2100 pixels 250 x 220 pixels (7‖ x 7‖ at 300 ppi) (~ 2.5 x 2.5 at 96 ppi)
  22. 22. Use JPG format for photographic or continuous tone images
  23. 23. Why use JPG format for photographic or continuous tone images? TIF GIF - 128 colors JPG - Medium 168 k 20 k 4k 58 seconds* 7 seconds* 1.3 seconds* *On a 28.8 kilobits per second dial-up connection
  24. 24. Use GIF or PNG format for graphics with solid colors
  25. 25. Why use GIF format for graphics with solid colors? TIFF LQJPG 4 color GIF 156 k 8k 4k 54 seconds* 3 seconds* 1.3 seconds* *On a 28.8 kilobits per second dial-up connection
  26. 26. Use ALT Tags (Alternate Text)
  27. 27. Formatting images for PowerPoint slideshow Original scan 1. In Photoshop, resize to 96 ppi (full screen is 10 x 7.5 inches) 2. Save as a High Quality JPEG (photos) or GIF (line art). 3. In PowerPoint, insert picture from file.
  28. 28. Leave room for text (if needed)
  29. 29. Take advantage of the drawing tools Cloud streets off the coast of New England
  30. 30. Find the right compromise between size & quality Moderate size, Smaller, but may be common file type* more trouble to produce 96 ppi 96 ppi 72 ppi 96 ppi TIFF HQ JPG LQ JPG 4-color GIF 204 k 120 k 8k 8k very large file size moderate file size small file size small file size very good quality good quality poor quality good quality *Note: If you use the Compress images feature in PowerPoint (Windows) all images are compressed to JPGs.
  31. 31. Use the smallest, best-quality files PHOTOS TIFF HQ JPG LQ JPG 4-color GIF 204 k 120 k 8k 8k (file size (file size large (small size (small size very large) quality ok) poor quality) best quality)
  32. 32. Formatting images for print Original scan 1. Resize to a dimensions in inches, and best resolution for paper size and printing device. 2. Adjust color mode if needed (grayscale, CMYK). 2. Save a copy as TIFF or PSD (Photoshop Document). 3. Send to printer or deliver to print shop.
  33. 33. How printing works Computer monitors use red, green and blue light to mix colors: Most digital printers use CMYK inks: CYAN MAGENTA YELLOW BLACK
  34. 34. How printing works Desktop inkjet Desktop laser Commercial photo Spay of water-based Screened patterns Laser exposed chemical CMYK dyes of CMYK toner photo prints
  35. 35. Offset Printing 4 color offset Rosette patterns of CMYK inks Spot color Solid areas of inks in specially mixed colors Pantone DS 62 – 1 C White paper
  36. 36. Formatting imagesfor video Original scan Cropped to 4:3 &resized to 720 x 528 1. Crop to aspect ratio for video (4:3 or 16:9). 2. Use RGB or Grayscale. 3. Save as JPG.
  37. 37. Formatting imagesfor video Original scan Cropped to 16:9 &resized to 1280 x 720 1. Crop to aspect ratio for video (4:3 or 16:9). 2. Use RGB or Grayscale. 3. Save as JPG.

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