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# of Pixels and Bits

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Photo Communications, Spring 2012
Columbia College Chicago

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### of Pixels and Bits

1. 1. 22-3530 - 01 PHOTO COMMUNICATIONS of pixels and bits
2. 2. Measuring pixels
3. 3. VECTOR IMAGESBased on points & paths, numerical Resolution independent
4. 4. RASTER IMAGES (bitmap)A mosaic of pixels (picture elements) Resolution dependent
5. 5. 1132 pixels 1430 pixels Raster = Resolution Dependent Each raster image is made of a speci c number of pixels (pixel dimensions)
6. 6. IMAGE DETAILEvery time you capture a digital image, you create a speci cnumber of pixels. Image detail is translated into differences between pixels that the camera registers at the time ofcapture. Increasing resolution degrades the true detail from the capture with a ‘best guess’ (interpolation).
7. 7. VIEW PERCENTAGE1430 x 1132 1024 x 768
8. 8. View percentage at 100%
9. 9. View percentage at 60%
10. 10. BIT DEPTH Every raster image contains a certain number of pixels.Every pixel contains a certain number of bits (ones or zeroes). The number of bits contained in each pixel is called the image’s bit depth. for example, If you are working with an 8-bit grayscale image, each pixel contains 8 zeroes or ones. 2 = 01010101 = 256 8
11. 11. 8 BIT vs (12 vs) 16 BIT
12. 12. BIT DEPTH AND FILE SIZE File size is directly connected to the number of bits contained in an image. For example, 8 bits = a byteIf an 8-bit grayscale image has a pixel dimension of: 1430 x 1132 = 1618760 pixels 1618760 divided by 1024 (a kilobyte) = 1580.82 1580 divided by 1024 (a megabyte) = 1.54 1 kilobyte = 1024 bytes 1 megabyte = 1024 kilobytes
13. 13. IMAGE SIZE WINDOWThree different ways of describingimage size:1. Image size2. Pixel dimensions (count)3. Document size: how the pixels are distributed in the “real world,” i.e., your printer
14. 14. Tone
15. 15. LEVELSHi-contrast Lo-contrast
16. 16. HISTOGRAMS EVERYWHERE
17. 17. TONAL KEYTonal character can be de ned in terms of light, dark, or average, or use the terms high, low, and medium key.high key medium key low key
18. 18. DESTRUCTIVE EDITS All tonal edits “damage” the le to some extent. Extreme edits to tone using levels or curves can leave large tonal ranges completelyempty. These gaps in the histogram create what is called banding or posterization.
19. 19. NON-DESTRUCTIVE EDITSUsing adjustment layersallows you to make tonaladjustments withoutpermanently deletingcapture data.
20. 20. SHADOW AND HIGHLIGHTBe sure to always keep an eye on maintaining shadow and highlight detail when making tonal edits.
21. 21. for lm: Expose for the shadows and develop for highlights for digital: Expose for highlights (most of the time)
22. 22. BLOWN OUTHIGHLIGHTS