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Profiling Your Scanner and Digital Camera

In previous articles we discussed profiling monitors and printers, how standard working spaces connect the two, and how to proof one device or process on another. Our objective is to match the original file on-screen and on the printer, or in the case of a proof, to match the device on which it will be printed.

By Rich Adams, GIA

These matching scenarios assume that we have a digital file that matches the original. If the photo was scanned, the file should match the original transparency or print. If the photo was captured with a digital camera, the file should match the original scene. This is possible by profiling the scanner or camera. Another benefit of profiling your scanner or camera is that if you have more than one device, you probably want them all to match.

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  • Color scanners and digital cameras "separate" continuous-tone photographs by recording them through red, green, and blue (RGB) filters. These devices don't "see" in color, but in shades of gray that are recorded as RGB values. It's no wonder that no two scanners match!

    How It Works
    Color management software helps scanners and cameras to actually "see" in color. It works by scanning a color target of several hundred color patches. A profiling program compares the colors in the scan with color measurements of the target, which represent the "actual" colors. The program then builds a profile that corrects the scanned colors to agree with the actual colors. The result is scans that match the original. If several scanners are profiled to match the original, then these scanners produce calibrated output and agree with each other.

    Since a digital camera is basically a scanner attached to the back of a lens, you can also profile your digital camera. This works best for repetitive studio shots, such as catalogs, where the lighting, subject distance, and other variables don't change.

    Profiling Programs for Scanners
    Leading programs for scanner profiling include those from GretagMacbeth, Monaco, Creo, and Heidelberg.

    You can profile a digital camera with a scanner-profiling program, but GretagMacbeth and Monaco have separate utilities for profiling digital cameras. These programs apply smoothing to the color target capture, and look outside the color gamut of the profiling target so that bright, saturated colors in subjects will be covered by the profile.

    Scanner profiling targets include (clockwise from lower right): the standard IT8 288-patch target, the 500-patch Hutchcolor target, and GretagMacbeth's i1 RGB scanner target.
    Scanning targets include the industry-standard IT8.7 targets, which were first developed by Kodak as the "Q60" targets and then turned over to the American National Standards Institute's (ANSI) Committee for Graphic Arts Technical Standards (CGATS). The IT8.7 targets available from Agfa, Fuji, and Kodak include a 5x7-in. print, 4x5" transparency, and 35-mm transparency.

    The IT8.7 targets are made to a specified color gamut that all color print papers or films, respectively, can achieve. Thus the film you're using may be capable of brighter, more saturated colors than those represented in the IT8 target. With these color gamut limitations in mind, color consultant Don Hutcheson, who used to be an engineer with the British high-end scanner manufacturer Crosfield (now part of FujiFilm), designs and manufactures his own targets. The Hutchcolor scanner targets, also available on Agfa, Fuji, and Kodak film and paper, consist of 500 color patches imaged to the media's full gamut.

    The Hutchcolor scanner target, developed by consultant Don Hutcheson, has 500 color patches and is made to the full gamut of the Agfa, Fuji, or Kodak film or paper on which it is made.
    This scatter diagram in LAB color space compares a standard 288-patch IT8 reflective scanner target (left) with a 500-patch Hutchcolor target (right). Note that, compared to the IT8, the Hutchcolor target has more colors and a larger color gamut (colors extend further from the origin).

    GretagMacbeth's Digital ColorChecker SG is a newly developed target for profiling digital cameras. The target is made with color chips that are painted, not photographic dyes as with scanner targets, and has good representation of neutral colors and fleshtones.
    For its digital camera profiling module, GretagMacbeth's Munsell Color division makes a special, 140-patch target known as the Digital ColorChecker SG. Rather than being imaged on film, the color patches in the ColorChecker are actually painted onto the media, giving them a larger color gamut more akin to products that will be photographed.

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    How to Profile Your Scanner

    1. Before starting to profile your scanner, make sure you have (A) a scanner profiling target, in transparency or print form, and (B) the corresponding measurement file for the target, which is a text file. The measurement file may be available on the manufacturer's web site.
      To profile your scanner, first scan the scanner target with color management turned off and save as a tiff file of 1.5-5.0 MB.
    2. Make a scan of the color profiling target.
      1. If your scanner supports ICC profiles, make sure the profile is turned off or set to "None." (You want to profile the scanner in the "raw" state. You don't want to "profile the profile.")
      2. If your scanner automatically determines the highlight (white point) and shadow (black point) of the image, make sure you crop the target so the scanner doesn't see the scanner glass or backing.
      3. When scanning the target, turn off sharpening so the target will be uniform in color.
      4. Set the resolution of the scanner to produce a scanned file between 1.5 and 5 MB in size in TIFF format. (More than 5 MB will slow down the profiling program, and less than 1.5 MB won't have sufficient information.)
    3. Open your color management program and follow the instructions for opening the measurement text file and scanned TIFF file.
      After capturing the scanner target, open the tiff file in your color management program, along with the reference file of target measurements. Compare the thumbnail of your measurement file (left) with your scan of the target (right) to make sure the patches correspond. If the patches don't match, it probably means your target wasn't cropped correctly and will produce a faulty profile.
      1. Open the scanned tiff file and crop to the target borders.
      2. Open the measurement file.
      3. If the program provides thumbnails of the scanned and measurement files, compare the thumbnails and make sure they agree.
      4. Make the profile, and save to the Profiles folder on your computer.

      Image before (left) and after (right) application of a scanner profile. The profile automatically corrects tone reproduction, gray balance, and color correction of the image based on the 288 or more color patches in the target.

    4. Test the profile to make sure it's accurate. In Photoshop, open the original scanned target used to make the profile. Apply your profile to the target using Photoshop's Image > Assign Profile command. Note whether the target matches the original more closely with the profile applied, and whether there are any artifacts. Also apply the profile to a photo that's been scanned without a profile on the scanner.

    To profile a digital camera, photograph the target using the same lighting and settings that will be used for the scene. Use the target capture to make the camera profile with a profiling program, then apply the profile to captures using your capture software (if it supports ICC profiles) or Photoshop's Image > Assign Profile command.
    How to Profile Your Digital Camera

    1. Make a capture of the reflective scanner target or digital camera profiling target.
      1. Set up the shot so the target is square, evenly illuminated, and free from glare.
      2. Gray balance your shot if your capture software allows.
      3. Save the capture as a raw TIFF file, with no profile attached. If your capture software doesn't allow saving a raw, gray-balanced TIFF file, you may need to capture into one of the standard RGB working spaces.
    2. Follow the scanner profiling steps 2-4 above for scanner profiling.

    Applying Scanner/Camera Profiles
    Once you've profiled your scanner or camera, how do you use the profile to get matching color?

    • If your scanning or digital capture program is ICC-compatible, it may have a pop-up menu for selecting an appropriate profile.
    • If your scanning or capture program isn't ICC compatible, you can apply the profile in Photoshop with the Image > Assign profile command.

    To use your scanner or camera profiles in a workflow, note that they are "source" profiles, they describe the color reproduction characteristics of devices where images originated. Apply the profiles with your scanning or capture software or using Photoshop's "Assign Profile" command. Then convert the images to a standard RGB working space as a "destination" profile. When displaying the image on-screen, the standard working space becomes the "source" and your calibrated monitor profile the "destination."
    What's the difference between Photoshop's "Assign Profile" and "Convert to Profile" commands? Think about the workflow, or movement of digital files from one device to another. "Assign Profile" refers to the device(s) from which an image came, such as a scanner, camera, or standard color working space. These are represented by source profiles. "Convert to Profile" refers to the device(s) to which files are going to be output, such as monitors, printers, or proofers. These are represented by destination profiles. Since scanners and cameras are image sources, the appropriate command for applying them is "Assign Profile."

    Once you assign the scanner/camera profile to an image, it should look more like the original than it did without the profile. Once assigning the profile, you can embed the profile into the image when saving it, so other operators who open the image will be able to see the corrected version. It may also be a good idea to convert your scanned/captured images to a standard working space profile, such as Adobe RGB, ColorMatch RGB, or sRGB. A standard working space profile is a place to store color data until you know what you want to do with it.

    If you profile your scanner(s) and digital camera(s), then, theoretically if you photograph the same scene digitally and on film that's scanned, all of the photos should match. Thus scanner and camera profiling have the potential to save a lot of time in reshooting, rescanning, and image editing.

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