62 lines
3.2 KiB
HTML
Executable File
62 lines
3.2 KiB
HTML
Executable File
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<title>Evauating Input Targets</title>
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<meta http-equiv="content-type"
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content="text/html; charset=ISO-8859-1">
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<meta content="Graeme Gill" name="author">
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</head>
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<body>
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<h2 style="text-decoration: underline; font-weight: bold;">Evaluating
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input targets<br>
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</h2>
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There are a variety of color profiling targets available for
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characterizing input targets, and it is sometimes hard to decide which
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one will be best for your particular purpose. Listed here are some
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criteria to evaluate:<br>
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<h4>Color gamut</h4>
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The resulting profile will only be accurate between or near the color
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values contained on the chart. This means that if the colors you are
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actually processing with your device go outside the gamut of your test
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chart, the color values will have been extrapolated by the profile, and
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are therefore likely to be not very accurate. <br>
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<h4>Color Resolution</h4>
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The profile will be most accurate for colors that are near those
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contained on the chart. This means that the more closely and evenly
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spaced within the color gamut the value of<br>
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the test chart are, the more accurate overall the chart will be. So
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typically the greater the number of test values, the better.<br>
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<h4>Dynamic range and White point</h4>
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Similar to color gamut, the profile will only be accurate over the
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range of lightness levels exercised by the chart. At the dark end the
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ideal black test value will be a light trap. At the white end the ideal
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white test value would be the perfect 100% reflective diffuser. In
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practice there is another consideration, which is that by default the
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white point of the profile is set by the white value of the test chart,
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and any values over this may be clipped by the profile. So ideally the
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white patches should represent the white value of the work you will be
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using the input device for.<br>
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<h4>Spectral similarity</h4>
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One of the fundamental problems with colorimetrically characterizing
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input devices, is that typically input devices don't have the same
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spectral sensitivity as a human observer. This means that it "sees"
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color differently, and that there is no way to perfectly compensate for
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this in a device profile. [There will be some spectral values that look
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the same to the device but appear different to us, and visa-versa.] A
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colorimetric profile will best compensate for such differences when the
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target test colors have the same spectral reflectance characteristics
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as the the intended work. What this translates to is that you will get
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best results when the test chart uses a similar printing process to
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whatever work you will be using the input device for. So if you are
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intending to scan photographic prints, you should use a photographic
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based test chart. If you were scanning artworks, then you should use a
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test chart that has pigments that are similar to paint used on such
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artworks, etc. When characterizing camera's, an additional source of
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spectral differences is the illuminating light source used. Once again,
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it will be best to choose a light source to characterize the camera
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that is going to be most similar to the light source you will typically
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shoot photographs under. <br>
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<br>
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</body>
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</html>
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