Staff Development Continuing Education Series:

What well discussPixels:Resolution and ResizingColorFile formatsHardware & Software

you say you want a re(s)olution

Digital Images and PixelsDigital 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.

Patterns of dots produce the effects of consistent colorThe size of each pixel is determined by print size.

Digital Images and PixelsThe 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.

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

The Big Picture=.5 x.75 @ 72dpi; 6.5 kb4 x 5 @ 10 dpi 6.5 kb

The Big Picture=Resolution SHOULD decrease when you enlarge, but if you scan at a high resolution, the loss wont be as severe.

The Big Picture4 x 5 @ 72 dpi 113 kb=.5 x.75 @ 575dpi; 113 kb

Changing the document size alone doesnt change the pixel dimensions or the file size

Before: 6.569 x 6.694 inches (473x482 pixels) 72dpi 667.9KThe number of pixels doesnt changejust the print size of them.After: 3 x 3.057 inches (473x482 pixels) 158 dpi 667.9K

Resolution

Print-Size

Print-size and resolution are inversely related

Resampling can change the number of pixels, which can therefore change the file size

Before: 6.569 x 6.694 inches (473x482 pixels) 72dpi 667.9KAfter: 3 x 3.057 inches (473x482 pixels) 72 dpi 139.3KResampling 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.After: 6.569 x 6.694 inches (105x107 pixels) 35 dpi 32.9K

Resolution

Print-Size

Resampling breaks the relationship between resolution and print size

A WarningIt is possible to resample up or interpolate. The computer adds in new dots and guesses their color. The quality is typically poor

=4 x 5 @ 72dpi 323 kb.5 x.75 @ 72dpi; 6.5 kb

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

Print QualityGood 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 cant appreciate detail higher than 300 dpi from about 8 inches distance

Monitor QualityRegardless 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

16(-bit) and what do you get?

Painting with PixelsWhat 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

Painting with PixelsHow 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 looksand the bigger the file is

Painting with PixelsMulti-channel Color (RGB)3 channels (R,G,B) @ 8-bit = 24 bits per pixel256 kinds of Red256 kinds of Green256 kinds of BlueCombined to make millions of colors 3 channels (R,G,B) @ 16-bit = 48-bits per pixel = 65, 536 kinds of Red65,536 kinds of Green65,536 kinds of BlueCombined to make BILLIONS of colors

1-bit, black and white8-bit grayscale

1-bit, black and white8-bit grayscale

1-bit, black and white8-bit grayscale24-bit color

8-bit grayscale24-bit colorWhich looks better to you?

24-bit color8-bit colorCan you tell the difference here?

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

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

Palatable PalettesThe proper color palette to use depends on the image and how you will use it

Palatable PalettesWhich Color Settings to Use?

1-bit: Black & White text with no artifactual value mainly for large-scale book scanning, ILL scanning8-bit, 1 channel: Indexed color or grayscaleweb graphics and thumbnails, NOT continuous tone imagestext with some artifactual value; sometimes with black and white images8-bit, 3 channels (24-bit): RGBmanuscript text, photographs, slides, etc.16-bit, 1 channel (16-bit): GrayscaleBest for grayscale images that will need major adjustment post-scan16-bit, 3 channels (48-bit): RGBBest for continuous tone images that will need major adjustment post-scan

save the last (file) for me

Saving and SharingRaw 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; doesnt 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 scheme but 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

Saving and SharingCompression:Lossless Compresses data but keeps the directions to reconstruct it. Doesnt compress as much as lossy compression.LossySimilar information is lumped together

Uncompressed image72 dpi8 bit RGB color83 KBCompressed image72 dpi8 bit RGB color30 KB

Uncompressed image72 dpi8 bit RGB color83 KBCompressed image72 dpi8 bit RGB color39 KB

Saving and SharingSo, 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?

(baby we were) Born to Scan

Flatbed ScannersPros:Reasonably good resolution and color managementCan be adapted to fit both reflective and transparent materialsStands up to repeated useEasy to use (usually)

Cons:Limited bed sizeLower resolution and quality than specialty scanners (some)

Slide or Film ScannersPros:High resolution Some models can handle both 35mm and medium slide formatsCons:Can only handle slide or film of specific sizesMore expensive than flatbeds

Overhead Scanners

Pros:Can handle oversize materials, fragile books, other odd formats or fragile materialsUsually come packages with software to do sophisticated image edits or batch processingSome have robotic page turning elementsCons:Difficult and time consuming to operateExpensiveLow resolution

Drum and Roll Scanners

Pros:Can accommodate large formatsCan capture in true CMYK colorsCapable of very high resolutionsCons:Materials must be sturdy yet flexibleCan damage materialsOnly appropriate for reflective materials

Scanning Software DifferencesDifferent interfaces have similar basic features

Epson InterfaceColor settings lists bit-depth but not RGBBoth resolution and print (document) size are changeableEpson Scan in Professional ModeScanning Software Differences

Color settings lists document types but not RGBBoth resolution and print (document) size are changeableEpson TWAINScanning Software Differences

Things to look for in a scannerHigh optical resolutionScanner specifications usually include an optical and interpolated resolution (and now we know interpolation is bad)D-max or dynamic rangeThe lightest light and the darkest dark the scanner can see. You want at least 2.0 (scale from 1.0 to 4.8)At least 24-bit external colorAnother trickinternal or hardware is meaninglessA transparency adapterIf you want to scan slides tooTake the manufacturers word with a grain of salt

Digital Cameras

Pros:Good for 3-dimensional objectsGood resolution and zoomCan capture materials from multiple anglesArea-array (vs. line-array)Cons:Quality can be dependent on skill of photographer and external factors like lightingProbably not as good for flat materials as a scanner

More ways to say the same thingMegapixelMaximum number of pixels in an imageResolution will depend on what size you print the imageWhen you open the image on your computer it will default to 72 ppiOptical Zoom vs. Digital Zoomoptical zoom is actual zooming with the lensdigital zooming is resampling! The quality