1. Lesson 2: Introduction to Digital Imaging Digital Photography MITSAA IAP 2003 Rob Zehner

2. Film vs. digital Film Mature technology Very high resolution Many form factors Low equipment cost Large infrastructure Can be archival Each exposure costs $ Harmful to the environment Digital Immature technology Low resolution Non-interchangeable Expensive equipment Little infrastructure Infinitely archival (?) Photos for free Environmentally friendly

3. Pixels, Resolution, etc. Pixel = picture element –Only appropriate for use with displays, input sources –1 pixel is the smallest unit in a digital file –a pixel can take on many intensities / colors Printers work in dots or lines –dots are typically either on or off –1 dot does not equal 1 pixel

4. Pixels, Resolution, etc. Color depth –Refers to the number of colors that each pixel can show –Given in bits -- for N bits, actual # is 2 N –For color, total depth is 3X the depth for each primary color (red, green and blue) Effective resolution is determined by color depth, dots per inch –# gray values = (printer res./screen frequency) 2 + 1

5. Pixels, Resolution, etc. “Resolution” is a misnomer –Usually refers to total number of pixels in an image (i.e. 3 megapixel camera) –May also refer to dpi or lpi –Meaningless without specifying a size for the output, and a corresponding color depth 150-300 dpi at 24-bit color is approximately photo-quality Computer monitors are usually 72-125 dpi at 24- bit color

6. Choosing a File Format Ultimate reference: –“Encyclopedia of Graphics File Formats,” O’Reilly Many possible ways to save your images There are advantages and disadvantages to each Many formats are closely tied to particular functions

7. Compression Compression is crucial for storing image files –A 3Mpix file with 24-bit color takes up 9MB uncompressed ! –This would make digital cameras impractical Two kinds of compression: lossless and lossy –Lossless: all original data is preserved –Lossy: Relies on information theory, human perception, to throw out info with low info content

8. Graphics File Formats GIF: Graphics Interchange Format –Developed by CompuServe –Only supports 256-color images (palette) –Lossless compression algorithm –Good for WWW supports animation, transparency TIFF: Tagged Image File Format –The Swiss Army Knife of graphics formats –Can be losslessly compressed, or uncompressed –Immense variability in type can cause problems

9. Graphics File Formats JPEG: Joint Photographic Experts Group –Very common format for photographs –Supports full color depth images –Lossy compression Can give artifacts User can typically adjust the compression ratio Artifacts are worst in images with solid colors, sharp lines

10. Graphics File Formats PNG: Portable Network Graphics –An up-and-coming format –Attempting to replace GIF, TIFF –Free from IP issues PSD: Photoshop Project File –AFAIK, only supported by PhotoShop –Allows multiple layers, history support, etc. –Good for storing works-in-progress