Scanning Photos

Scanning and correcting photos ready for black and white printing can be reliable - try following these steps. We find this gives us good results first time - most of the time.

You will need a 256 greyscale (or colour) scanner and a photo editing program such as Aldus Photostyler, Adobe Photoshop or Corel Photo-paint.

1. Set the scanning resolution at 130% of the line screen the photo will be printed at (normally 85 lpi x 1.3 = 110 dpi). If you are enlarging or reducing the photo, set the percentage for this before you do the scan, rather than stretching or shrinking the size in your layout package.
2. Make your scan 256 level greyscale
3. Next, use the grey scale correction features of the photo program to adjust the brightness in the darkest and lightest areas of the scan.
   This ensures that the final halftone dots are the correct size for printing by adjusting the output range settings on the correcting graph to bring back the output levels slightly from full black and white.
   The amount you bring the levels back will change with the type of printing plates to be used. For normal bromides and paper plates use 20 & 245 (8% & 92%), and for negatives and metal plates use 12 & 245 (5% & 95%).
   If your original photo has a very bright light source or reflection in it (called a specular highlight) you can extend the upward number to 255 (100%).
4. The next step is to adjust the contrast of your scan for best effect. If your original was very dark or very light re-scale the input range over the output range.
   This can be done automatically in most programs (in Photostyler use the toolbox option inside the Grey/Colour Correction box called "Auto Ranging"), or manually by sliding the input range settings to the upper and lower ends of the scan data, using the histogram information in the graph to locate the ends. If your original photo was good, you probably don't need to do this.
5. You can also apply a gamma correction to the scan. The amount of correction is objective, and you will have to try different settings and preview them to get the best result. The gamma correction applies a non linear mapping between the input and output data, tending to boost detail in the darker areas of the scan and reduce it in the lighter areas. Adjust the Gamma to achieve the clearest looking image on the screen.
6. Once you are happy with the preview of your scan, save it as a TIFF file, ready for use in your page layout package.

Generally you can get any photo up to an acceptable standard just by manipulating the values in the grey correction section of your program (ie. up to Step 3). The filters provided with programs to sharpen images etc. are rarely needed once you have a good understanding of grey correction. It is worth experimenting with the controls in this section of the program to develop a feel for how they affect a scan.

Do not try to adjust your scan by holding the photo next to the screen and making adjustments so the screen matches the photo. The screen display will not accurately reflect the scan data unless you have calibrated your monitor. Use the program to read off the darkness in the sections of the scan that you are concerned about, and make any adjustments based on that.