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Using Reference Strips

Using Reference Strips

Color and grayscale targets can be used to help ensure that the color and tone metrics of the scanner are captured along with the image of the object itself. A reference strip can be useful both before the full scan takes place and after it. After a pre-scan of the material, most scanning software will show you how color and tone will appear in the final image. You can use the reference strips at this point to change both color and tone settings for the scan so it matches the original. This can be done after the full scan in Photoshop as well. Even years later the strips may provide a useful reference point when the original is no longer available for direct viewing.

  • Targets can be scanned along with each object as it is scanned, called an "internal" target, or scanned separately for an entire batch of scans or for each scanning session, called an "external" target. Keeping track of external target may prove to be a problem over time. Therefore it is recommended that if you use targets at all, scan the target along with each object.

  • Place the target (e.g., Kodak Q-13, "Kodak Color Separation Guide and Gray Scale") along the margins of the object itself Placement of the strips should be consistent to allow them to be automatically cropped out (e.g., from Delivery Files) and to minimize the amount of space they consume.

Before Full Scan

You should also examine and test the tone and colors in the Reference Strips at this point to make sure the scanner is properly calibrated and representing tone and color properly. A minimum of 18 steps should be visible on the 20-step grayscale (Kodak Q13) Reference strip. If not, there is a risk not capturing details that reside in the gray areas of the original. For reflective scans there should be a minimum of 5.5 f-stops (6 f-stops or 1.9 db is preferred) and for transmissive scans there should be a minimum of 8 f-stops (10 f-stops or 3.0 db is preferred).

35 mm slides can be scanned alongside a Kodak Q-60 Color Input (Q-60E3 for Ektachrome and Q-60K3 for Kodachrome file). Other sizes of transparencies such as negatives and film can be scanned with targets specifically designed for them.

Steps

  • Do a pre-scan.

  • Open the densitometer (find the Info palette) (When you're working in RGB, the Info palette can show you how pixels will translate into grayscale.)

    Kodak Q-13 Target Values
      A M 19 B (alternative)
    RGB levels
    (accepted range)     		242-242-242
    (239-247)     		104-104-104
    (100-108)     		12-12-12
    (8-16)     		24-24-24
    (20-28)
    % Black
    (accepted range)     		5
    (3-6)     		59
    (58-61)     		95
    (94-97)     		91
    (89-92)

    • Click on the small triangle in the upper right corner, click on Palette Options, and set Mode to "Actual Color." Set Second Color Readout to "Grayscale."

    • Place the cursor over the A, M, and 19 areas of the Kodak Q-13 target.

    • Compare the control R, G, B values in the image with the R, G, B values for particular grayscale patches of the Kodak Q-13 target. The after values for R, G, and B should be within the acceptable range for these patches according to the chart below and should be within four levels of each other.

    • If the levels do not meet the standards, repeat the steps above until the proper levels are achieved.

    • The black and white sliders should always be adjusted before the gray slider (the middle one) is adjusted. Adjust each slider as follows:

      • If the levels in area 19 of the target (the blackest square) are too high adjust white slider to the right. If they are too low, adjust them to the left. In most images the white slider will be set to 255.

      • If the levels in area A of the target (the whitest square) are too high adjust the black slider to the left. If they are too low, adjust the slider to the right.

      • Adjust the gray slider to the right if the levels in area M of the target (the notched gray square) are too high, to the left if they are too low.

      • Once the grayscale swatches of the Q-13 target appear to be within the proper ranges, close the histogram adjustment tool.

After Full Scan

You can determine the color values of any part of an image after it has been scanned by using Photoshop's Info palette (File> File Info). After you open the Info palette, position the pointer over any part of the image, and the color value under the pointer will be displayed at the top left column of the palette. For example, when you place the pointer over the gray frame of the Reference Strip, all the color values will be 96, indicating pure gray. When you are viewing the Reference Strip, your image should be displayed in RGB mode. You can verify this by making sure that the left column shows RGB. Refer to the Adobe Photoshop manual to interpret these color values.

If the Capture File has a reference strip in it, the strip needs to be retained in the Archival Master File, but it is usually cropped out of the Working Master File and the Delivery Files.

Resources for Using Reference Strips

 

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