While the basic operation of scanning is fairly simple, it involves making a number of choices along the way. Since the choices are more confusing than the actual process, this page will help you make these choices so that your scan meets your needs.
In general, your goal is to get the best clarity with the smallest file size so that your graphics do not take too long to print or to appear on the Web.
Choose a resolution in dots per inch (dpi).
Scan your image in the highest dpi you will be needing. The PhotoShop or IrfanView software can reduce the resolution without rescanning.
The NOBLE standards are as follows:
- Master Copy (optional but recommended)
Used for a master copy for preservation, can be used to generate high quality reproductions. Often saved to CD-ROM for preservation. In photos with large amount of detail (group photo of graduating class, for example) access can be provided as an option on the Web.600 dpi, JPEG for Web viewing, uncompressed TIFF file for future print reproduction.
Color originals: 24-bit (JPEG) or 42-bit (reproduction file). Black and white originals: photographs and other halftones: 8-bit grayscale; printed materials, 8-bit grayscale.
Scan size: 1:1 - Access copy
300 dpi, JPEG or GIFF
Color: 8-bit; black and white photograph, grayscale; printed materials grayscale or 1-bit black and white.
Scan size, 1:1
Display size, 640 pixels horizontal for Web display. - Thumbnails
72-75 dpi, JPEG
Color: 8-bit; black and white photograph, grayscale; printed materials grayscale or 1-bit black and white.
Display size, minimum of 100 pixels horizontally, maximum 200 pixels.
Negatives, slides, etc., should be upsized to standards above.
Do a preview and make a crop; then scan.
First run a Preview. Then with either scanner, crop to make the scanned area as small as possible, yet include desired subject. Do this by dragging the frame from the corner around the subject or have PhotoShop automatically select the image, adjusting as necessary. When OK, click Scan.
Choose a size; adjust subject and colors, check the ratio.
If you are importing the scan into a page layout program, the scan size is not as important since you can size it in the layout program. However, scans for the Web should be a size reasonable for a screen. From the Image menu, choose Size if you wish to change size or resolution of your
scan. The resolution will change as you change the size, so be sure to reset the resolution box to “not selected” when you’re working with the image/size menu. You can also change the resolution. Be careful about this step; you can not regain resolution it has been decreased. It is wise to save versions of your scan as you go along so you can return to previous versions.
- Ratio: This is an important step in PhotoShop for Web scans. Look at the top of the scan; you will see a ratio like 1:1 or 1:4, etc. Make certain this reads 1:1 before you save. To change this ratio, pull down the view menu and work with the scale up and scale down features.
Review of the steps:
- Preview the image to be scanned.
- Adjust the marquee, that is crop to the desired image area.
- Scan at the highest needed resolution – 600 dpi for archival or detailed copies, 300 dpi for standard Web access copy.
- Minimize Twain software and save 600 dpi image in JPEG or TIFF format as appropriate (see below).
- Pull down Image menu and Resize size (640 pixels) and resolution (300 dpi) for Web access copy.
- Minimize Twain software and save 300 dpi image as JPEG or GIF format (see below).
- Pull down Image menu and Resize resolution (75 dpi) for Web access copy. Largest dimension should automatically resize to between 100 and 200 pixels per inch. If not within those bounds, manually resize.
- Minimize Twain software and save 75 dpi image as JPEG or GIF format (see below).
Choose a name for the file.
This tutorial from the UNC discusses the importance of file naming and suggests file naming strategies.
Choose a save format for the scan.
When you complete your scan, you may choose what format you wish to save in. Choose a format depending on your plans for the scan.
- PhotoShop: Choose this one if you want to be able to make further adjustments. Often you should keep one copy in this format and make a second in another format.
- Tiff: This is the best one for most page layout programs and Word. Features such as coloring, shading and posterizing will work in QuarkXpress, for example.
- For the Web: The last step in preparing a file for the Web is saving it as a GIF or JPEG file.
You can use graphics in either gif or jpg formats, which can be displayed by most browsers without the use of plug-ins. As a general rule, jpg is better for photographs and gif is better for everything else. This is because jpg handles gradations of color better, and gif handles sharply defined areas better. When in doubt, try both and use the one that looks better and stores at the smaller size.