Scanning and Digital Imaging Basics Digital Initiatives Team October 18, 2006 Gretchen Gueguen

Introduction What will we cover? –What do I need to know about digital images? –How do I make/edit digital images? –How do I use digital images? Why are we covering it? –To ensure a level of quality in images that we scan. –To ensure a level of quality in images that we keep for archival purposes.

Digital Images and Pixels What are Digital Images Made of? Digital elements called pixels. –Pixels are bundles of digital information. They are organized into a grid to convey the image. Dimensions of the digital image are given in pixels. Image elements called dots. –Dots are smallest unit of a color. The more dots in an inch of the picture, the better it looks. This aspect is called resolution. Print size –Pixels determine the size of the digital image, but the print size determines what you will see on the screen or when you print out an image.

Patterns of dots produce the effects of consistent color

The many sizes of Testudo Changing the document size alone doesnt change the pixel dimensions or the file size

Before: x inches (444x289 pixels) 72dpi 375.9K Pixel size Print size After: 3 x inches (444x289 pixels) 148dpi 375.9K

The many sizes of Testudo Resampling changes both the pixel dimensions, the print size, and the file size.

Before: x inches 444 x 289 pixels) 72dpi 375.9K After: 12 x inches 864 x 562 pixels 72dpi 1.39 M Pixel size Print size

Digital Images and Pixels The ratio of the number of dots to the PRINT size is the Resolution. –Resolution is used to judge the quality of the image. The higher the resolution, the sharper the image details are. –Resolution should change as print size changes if the image is not resampled. –Resolution is most often measured in dots per inch or dpi.

Digital Images and Pixels What are pixels made of? Pixels are groups of digital information – groups of bits (0 or 1) that give directions for different colors –The number of bits in the pixel determines the color palette: More bits = more combinations = more possible colors This is called bit-depth and it is closely related to color profiles or modes

Color profile and bit-depth 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, etc.) –8-bit = 256 colors ( , , etc.) The more colors you can use, the more realistic a picture looks

Color profile and bit-depth So can I get more than 256 colors? –3 channels 8-bit = 8-bit/channel, or 24-bit/ pixel millions of colors Can I get even more than that? –3 channels 16-bit = 16-bit/channel or 48-bit/pixel = millions of colors x 2

The Big Picture Which Color Profile to Use? 1-bit: –Black & White [text with no artifactual value mainly for large-scale book scanning] 8-bit, 1 channel: –Indexed color [web graphics and thumbnails] –Grayscale [text with some artifactual value; rarely with black and white images] 8-bit, 3 channels: –RGB (red, blue, green, the primary colors of light…and your monitor) [manuscript text, photographs, slides, etc.] 8-bit, 4 channels: –CMYK (cyan, magenta, yellow, black, the primary colors of ink used in printing) [images destined for offset printing]

The Big Picture Next you need to decide how many dots to use to capture your image. Theoretically, the more you cram in the better the image is, right? Answer: yes and no –Image quality relates both to the number of dots of color and the size at which the image is displayed. –Once the image is scanned, dots can be stretched or compressed but should not be added.

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

The Big Picture = 72dpi; 18.5kb 19 dpi 18.5kb

The Big Picture However, keeping resolution constant results in interpolation. The computer adds in new dots and guesses their color.

The Big Picture = 72dpi 4.6Mb 72dpi; 18.5kb

The Big Picture

So the only reliable way to increase the size of an image (or zoom into a detail) is to scan at a higher resolution than what you would need at the regular size How do you know what resolution you need? –Print limitations: 280 to 300 dpi –Screen limitation: 72 dpi –Institutional Guidelines

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 Picture 300 dpi 95kb 72 dpi 95kb =

The Big Picture If we want to create a smaller file size, we can change the print size and resolution through resampling as long as the resulting image decreases these values and still meets the needs of viewing medium.

Saving and Sharing Now that we know what settings to use to make a good image, how do we save it? –Need a copy to keep (hi-res, original size, big file) –Need a copy to print (med- to hi-res, determined size, big to medium file) –A copy to view (lo-res, determined size, small file) –A copy for comparison (lo-res, small size, small file)

Saving and Sharing Other factors that affect file size: –Compression: Lossy –Similar information is lumped together Lossless –Compresses data but keeps the directions to reconstruct it. Doesnt compress as much as lossy compression.

Saving and Sharing –Format: TIFF files are usually the largest because they can be uncompressed or compressed using a lossless method. JPEG files use a lossy compression and are much smaller than TIFFs GIF files also use lossy compression in combination with an index color scheme making them very small. For archival purposes a TIFF file is usually kept as a master file. JPEGs are created as high-quality derivatives and GIFs may be created for use as thumbnails.

Making Decisions Now that you understand some of the variables, resources exist to help you make decisions –Best Practices for Digital projects –Workshop handouts –Digital Collections and Research

Scan Interfaces What variables can I control when scanning? –Color profile/bit depth –Resolution –Size –Histogram balance / Tone Curve

Scan Interfaces Epson Interface Color settings lists bit- depth but not RGB Both resolution and print (document) size are changeable The histogram tool is opened from here. It will adjust the exposure settings Epson Scan in Professional Mode

Scan Interfaces Epson Scan in Professional Mode Histogram input sliders and levels Histogram output sliders and levels

Microtek Interface Resolution and print size settings Color settings Open Color Correction tool Open Tone Curve tool Scan Interfaces Preview Window Overview, Prescan, and Scan buttons Open correction tools

Scan Interfaces Microtek Interface Info window Color wheel

Scan Interfaces Microtek Interface Interface with a correction tool open

Scan Interfaces Nikon SuperCoolScan 5000ED (for slides) Color options are: Calibrated RGB or Grayscale Preview and scan buttons Option to see the image with or without corrections Keep this File Size and Resolution controls

Scan Interfaces Curves palette does the same thing as the histogram adjustment in the Epson scanner. Nikon SuperCoolScan 5000ED (for slides)

Examples of Noise, Distortion, Channel Problems Fixed pattern noise Random noise Banding Moiré patterns Channel misalignment