Scanning Basics
Teaching Scanning without a scanner by your side is like teaching driving without a car or
cooking without the ingredients! Transforming a photographic original into a digital file is done by a device called a scanner. The scanner measures the color value of light that shines through the original (for transparencies) or reflects off it (for reflective art) and records those values in an electronic file.

The image is sampled (measured) at thousands of points, and each sample is recorded as a separate pixel (picture element) made up of different values or red, green and blue, the primary colors for light. The resulting bitmap can then be reconstructed on a computer screen or printer.
A good scan is as important as a good original to successful reproduction of an image. Neither digital retouching nor high-quality output can make up for inadequate scan.
Scanners capture the color information of an image in the RGB color mode.

The quality of a scan is affected by:
- the quality of the scanner's optical mechanism, which controls its ability to capture a broad dynamic range (variations in light and shadow)
-the resolution(number of samples per inch) of the scan
- the scanner's pixel depth, which controls the number of colors it can capture.

Scanners can be divided into three primary types

- Drum scanners, in which the original wraps around a drum that is rotated next to a light source

- Flatbed scanners, in which the original rests on top of a glass plate, which the light source and sensors move past.

- Slide scanners give the best results for slides and negatives.

History of Desktop Scanners

1985 first desktop scanners became available.
Thunderscan scanner wasattached to a dot matrix imagewriter printer. It used the transport mechanism of the printer to move the image during scanning.
It took 20 minutes to capure a 3"x 5" image at 200ppi.
The image then appeared on a 9" black and white monitor.

Desktop scanners
Designers still have photographs professionally scanned. As scanning technology and image manipulation has improved we(designer) have become the scanner operator.
1. higher resolutions for desktop scanners
2. wider tonal ranges in newer scanners
3. quality and capabilities of software, scanning and image manipulation

Advantages of scanning your own images
1. Creative control
2. experimenation
3. cost
4. time saved

Scan for specific output device
Monitor /Web
- scan at 72 dpi
Print Offset
- scan at 300dpi
Inkjet Printers- scan at 1/3 of the printer resolution
- 720 dpi inkjetprinter - scan image at 240 dpi

Up and Down Sampling after Scanning

Most image processing programs (Photoshop) provide ways to change the resolution of your file after you have scanned it:
- downsampling will reduce the resolution. When you downsample(or decrease the number of pixels), the software simply throws away the pixels it doesn't need.

- upsampling (increasing the resolution) will increase the resolution.
When you upsample, (or increase the number of pixels), new pixels are added based on color values of adjacent pixels. This is called interpolation.

Interpolation allows you to create greater image resolutions that your scanner is capable of producing.

Interpolation can tend to blur the image.

If the file has more resolution than you need for your printing method, it also allows you to discard extra pixels to reduce the image file size.

Resizing an image will also have an effect on the image file's resolution.

Moire Patterns in Scans

Undesirable patterns, fine herringbone or crosshatched pattern, in the light areas of images which are offset printed(magazine images) and are being rescanned.

Moire Patterns are caused by interference between two sets of fine pattern grids, in this case, the scanner cells(pixels) and the halftone screen in the printed piece. Moire Patterns can be avoided only if you scan at a higher resolution than the printing screen.

When scanning an image from a book or magazine,this image is already a halftone.
To prevent a moire pattern,
1. scan the image at at least 2x the finished size you need.
2. In Photoshop, reduce the image to the correct size in Image Size box
3. In Photoshop, use the median option to get rid of the artifacts.
4. In Photoshop, Unsharp mask to get the best sharpness.

OR
1. scan the image at 2x the resolution you need.
2. In Photoshop, reduce theresolution to the correct size in Image Size box
3. In Photoshop, use the median option to get rid of the artifacts.
4. In Photoshop, Unsharp mask to get the best sharpness.

Oversharpening after Scanning

The scanning process may cause some loss of detail and edge definition in an image. To correct for such softening, some scanners have automatic sharpening routines built in.

Most often, however, you will need to sharpen the scanned image using sharpening filters found in the scanning or image-manipulation software.
The most common filters are called sharpen, sharpen more, sharpen edges and unsharp mask. Sharpen and sharpen more sharpen the entire image (of a selected portion of it), by increasing the contrast of adjacent pixels. Sharpen edges and unsharp mask increase contrast only at the image's edges, or areas in which lines of different colors meet, preserving the overall smoothness of the image but increasing object definition.
For photographic images, unsharp mask is the most effective sharpening filter. (The others are more often used for line art.)

Unsharp mask is designed to create lighter and darker areas on each side of an edge. Unsharp mask tools generally offer controls for adjusting the degree of contrast (the 'amount setting'), the area on each side of an edge that will be affected (the 'radius'), and how different adjoining pixels must be before they are affected ('threshold'). Using high settings or repeating the unsharp mask operation could oversharpen the image, resulting in a halo effect around edges.

The unsharp mask filter is also useful when an image has lost definition during resizing. (During resizing, the software may create extra pixels by interpolating between adjacent pixels, thus softening the image.)