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Digital Imaging Basics

Staff Development Continuing Education Series:. Digital Imaging Basics. What we’ll discuss…. Pixels: Resolution and Resizing Color File formats Hardware & Software. “you say you want a re(s)olution”. Resolution and Resizing. Digital Images and Pixels.

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Digital Imaging Basics

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  1. Staff Development Continuing Education Series: Digital Imaging Basics

  2. What we’ll discuss… • Pixels: • Resolution and Resizing • Color • File formats • Hardware & Software

  3. “you say you want a re(s)olution” Resolution and Resizing

  4. Digital Images and Pixels Digital Images are composed of digital elements called pixels. • Pixels are bundles of digital information about the color of a specific spot in the image. • They are organized into a grid to convey the image.

  5. Patterns of dots produce the effects of consistent color The size of each pixel is determined by print size.

  6. Digital Images and Pixels The RESOLUTION is the ratio of the number of PIXELS to the PRINT size. Resolution = # of pixels on the longest side print size Resolution is • used to judge the quality of the image. • Most often measured in pixels (or dots) per inch or ‘ppi’.

  7. The Big Picture = Increasing size without increasing resolution stretches out the dots of color.

  8. The Big Picture = .5 x.75 @ 72dpi;6.5 kb 4 x 5 @ 10 dpi6.5 kb

  9. The Big Picture = Resolution SHOULD decrease when you enlarge, but if you scan at a high resolution, the loss won’t be as severe.

  10. The Big Picture = .5 x.75 @ 575dpi;113 kb 4 x 5 @ 72 dpi113 kb

  11. Changing the document size alone doesn’t change the pixel dimensions or the file size

  12. Before: 6.569 x 6.694 inches (473x482 pixels)72dpi667.9K After:3 x 3.057 inches (473x482 pixels)158 dpi667.9K The number of pixels doesn’t change…just the print size of them.

  13. Print-size and resolution are inversely related… Print-Size Resolution

  14. “Resampling” can change the number of pixels, which can therefore change the file size

  15. Before: 6.569 x 6.694 inches (473x482 pixels)72dpi667.9K After:3 x 3.057 inches (473x482 pixels)72 dpi139.3K After:6.569 x 6.694 inches (105x107 pixels)35 dpi32.9K Resampling can be done to any of the variables (print size, number of pixels, or resolution) independently of each other. Resampling breaks the relationship between the variables. It always results in file size change because I add or take away pixels.

  16. Resampling breaks the relationship between resolution and print size Print-Size Resolution

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  18. ≠

  19. A Warning… ≠ It is possible to resample up or “interpolate”. The computer adds in new dots and guesses their color. The quality is typically poor…

  20. = .5 x.75 @ 72dpi;6.5 kb 4 x 5 @ 72dpi323 kb

  21. Why Resample? Resampling is used to change image quality for specific purposes…

  22. Print Quality Good consumer printers can print up to about 275 ppi. Commercial printers are often much better. 300 dpi is a print industry standard. The human eye usually can’t appreciate detail higher than 300 dpi from about 8 inches distance

  23. Monitor Quality Regardless of the print size you dictate, the monitor will always display 72 pixels in each inch (unless your browser program creates a temporary view). If you scan something at 300 ppi and show it on a monitor, it will be resized to 72 ppi meaning a 5 inch image would be 21 inches. These images look as good as print images to your eye because of optical illusion

  24. “16(-bit) and what do you get?” Color palettes

  25. Painting with Pixels What are pixels made of? • Pixels are a string of code (a series of 0s or 1s) that signify directions for different colors. • Each 0 or 1 is called a “bit.” • The number of bits in the pixel determines the color palette. More bits = more combinations = more possible colors This is called ‘bit-depth’

  26. Painting with Pixels • How does bit-depth affect color? • 1-bit = two colors (0 or 1 for each pixel) • 2-bit = four colors (00, 11, 01, 10) • 4-bit = 16 colors (0000, 0001, 0100, 0101, 0111, etc.) • 8-bit = 256 colors (00000000, 001…, 010.. 011..., 001…, 111…) • 16-bit = 65,536 colors (00000…, 000…, 0…, 0…, 0…, 0…, 0…) • The more colors you can use, the more realistic a picture looks…and the bigger the file is

  27. Painting with Pixels • Multi-channel Color (RGB) • 3 channels (R,G,B) @ 8-bit = 24 bits per pixel • 256 kinds of Red… • 256 kinds of Green… • 256 kinds of Blue… • Combined to make millions of colors • 3 channels (R,G,B) @ 16-bit = 48-bits per pixel = • 65, 536 kinds of Red… • 65,536 kinds of Green… • 65,536 kinds of Blue… • Combined to make BILLIONS of colors

  28. 1-bit, black and white 8-bit grayscale

  29. 1-bit, black and white 8-bit grayscale

  30. 1-bit, black and white 8-bit grayscale 24-bit color

  31. Which looks better to you? 8-bit grayscale 24-bit color

  32. 8-bit color 24-bit color Can you tell the difference here?

  33. 8-bit or 24-bit? Can you tell the difference here?

  34. 24-bit or 48-bit? Can you tell the difference here?

  35. Palatable Palettes The proper color palette to use depends on the image and how you will use it…

  36. Palatable Palettes Which Color Settings to Use? 1-bit: Black & White • text with no artifactual value mainly for large-scale book scanning, ILL scanning 8-bit, 1 channel: Indexed color or grayscale • web graphics and thumbnails, NOT continuous tone images • text with some artifactual value; sometimes with black and white images 8-bit, 3 channels (24-bit): RGB • manuscript text, photographs, slides, etc. 16-bit, 1 channel (16-bit): Grayscale • Best for grayscale images that will need major adjustment post-scan 16-bit, 3 channels (48-bit): RGB • Best for continuous tone images that will need major adjustment post-scan

  37. “save the last (file) for me” Saving and sharing

  38. Saving and Sharing Raw formats : straight from the camera or scanner; no post-processing or organizing the data; only usable in a very limited number of applications TIFF : usually the largest digital files; supports many color profiles; different options for compression; cannot be displayed in a browser or email JPEG2000 : smaller than TIFFS; supports multiple color profiles; different options for compression; doesn’t work in many browsers or email JPEG : much smaller than TIFFs; viewable in web browsers; variable amounts of compression GIF : very small files using an index color schemebut uncompressed; viewable in any browser. PDF : great for sharing, especially text; web compatible; an open standard though not always a preservation one; not ideal for saving/reusing images

  39. Saving and Sharing • Compression: • Lossless • Compresses data but keeps the directions to reconstruct it. Doesn’t compress as much as lossy compression. • Lossy • Similar information is lumped together

  40. Uncompressed image 72 dpi 8 bit RGB color 83 KB Compressed image 72 dpi 8 bit RGB color 30 KB

  41. Uncompressed image 72 dpi 8 bit RGB color 83 KB Compressed image 72 dpi 8 bit RGB color 39 KB

  42. Saving and Sharing • So, how do we save it? • A copy to keep? (hi-res, original size, big file) • Tiff? JPEG2000? • A copy to print? (med- to hi-res, determined size, big to medium file) • A 300 dpi JPEG? JPEG2000? A PDF? • A copy to view? (lo-res, determined size, small file) • A 72 dpi JPEG? JPEG2000? A PDF? • A copy for comparison? (lo-res, small size, small file) • A 100x100 pixel JPEG? A 100x100 pixel GIF? JPEG2000?

  43. (baby we were) Born to Scan Setting Up Shop

  44. Flatbed Scanners • Pros: • Reasonably good resolution and color management • Can be adapted to fit both reflective and transparent materials • Stands up to repeated use • Easy to use (usually) • Cons: • Limited bed size • Lower resolution and quality than specialty scanners (some)

  45. Slide or Film Scanners • Pros: • High resolution • Some models can handle both 35mm and medium slide formats • Cons: • Can only handle slide or film of specific sizes • More expensive than flatbeds

  46. Overhead Scanners Pros: • Can handle oversize materials, fragile books, other odd formats or fragile materials • Usually come packages with software to do sophisticated image edits or batch processing • Some have robotic page turning elements Cons: • Difficult and time consuming to operate • Expensive • Low resolution

  47. Drum and Roll Scanners Pros: • Can accommodate large formats • Can capture in true CMYK colors • Capable of very high resolutions Cons: • Materials must be sturdy yet flexible • Can damage materials • Only appropriate for reflectivematerials

  48. Scanning Software Differences Different interfaces have similar basic features

  49. Scanning Software Differences Epson Scan in “Professional Mode” Color settings lists bit-depth but not “RGB” Both resolution and print (document) size are changeable Epson Interface

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