Scanning Basics and Tips

In order to scan images using a flatbed or slide scanner you have to make several decisions in advance, and plan what you are going to do with the images you scan before you scan them, so that you can get the best results.

A. To scan images you need to know:

• Source: color or black & white, photo or negative or slide
• Destination: print or screen (presentation or web)
• How you will store the scanned files

Suggestion: group images with similar characteristics: color or black and white, photo or negative or slides, final destination for image (screen or print.) Fill the scanner bed with images and use Photoshop to separate them, and rotate, as necessary. If you have a lot of scanning to do, this will save time.

B. The type of source image determines the scanner:

• Always try to scan slides and negatives in a slide scanner
• A flatbed scanner works well for photos and drawings

Suggestion: some flatbed scanners have slide or transparency adapters which can produce acceptable results. Slide scanners are made to project light through the material, and scan at significantly higher resolutions than most flatbed scanners.

C. Scan resolution determined by destination for image:
Basic guidelines:

1. 100-150 minimum for screen
2. 200-300 minimum for photos
3. 300-600 minimum for line art
4. Increase the resolution to enlarge the image
5. To print at twice the original size, double the resolution

Always scan images at a higher resolution than you think you will need. You can always reduce the amount of data through cropping, reducing the resolution or compressing the file, but you can't add it back in successfully.

If you scan an image at screen resolution, it will never print properly. When in doubt scan at a higher resolution than you think you need.

D. Scan color or bit-depth usually match source:

1. Scan color photos at 16 bit (true color) or higher
2. Scan black & white photos using grayscale (8-bit)
3. Scan line art using grayscale (8-bit) for screen
4. Scan line art using black & white (1-bit) for print
5. The more color you scan, the larger the file size.
6. For color photos, the more color you capture when you scan, the more accurate the final product.
7. For black & white photos, scanning them in color adds information that is unnecessary, inflating the file size.
8. You can take the color out later, but you can't put it back in, nor can you increase the number of colors later.

E. Don't use the scanner software to process the image:

1. DO use the scanner to accurately digitize the image
2. DO rotate or crop the image as you scan it
3. DON'T do color correction, unsharp masking, sharpening
4. Photoshop has much better tools for altering images
5. Use the scanner software to get the image into the computer. Save the file in its unaltered state, then open a copy and experiment with correcting it. You can always create additional copies of the original and manipulate them until you get the result you want. If you process while scanning, you may have to go back and re-scan if the correction doesn't work the way you expect.
6. Processing a scanned image with Photoshop's more powerful tools will also usually give better results.

F. After scanning save as the appropriate file type:

• gif for limited colors with crisp definition
• jpeg for continuous tone images (photographs)
• pict or tiff for complete accuracy (very large file sizes)

GIF: Graphic Interchange Format

• Reduces file size by limiting colors to 256

JPEG:Joint Photographic Experts Group

• Compresses file size by approximating data

PICT: abbreviation for PICTure

• Mac file format for bitmapped images, uncompressed

TIFF: Tagged Image File Format

• PC file format for bitmapped images, uncompressed

See also: http://www.scantips.com A very comprehensive web site for scanning information.