367 lines
16 KiB
HTML
Executable File
367 lines
16 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>illumread</title>
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<meta http-equiv="content-type" content="text/html;
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charset=windows-1252">
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<meta name="author" content="Graeme Gill">
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</head>
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<body>
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<h2><b>spectro/illumread</b></h2>
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<h3>Summary</h3>
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Use an instrument or instruments to measure an illuminant spectrum,
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including estimate its Ultra Violet content. A combination of direct
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illumination readings and readings from a piece of paper having some
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FWA content are used for this. (If the UV content is not needed, or
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a suitable instrument is not available, then <a
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href="spotread.html">spotread</a> should be used instead.)<br>
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<h3>Usage Summary</h3>
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<small><span style="font-family: monospace;">illumread [-options]
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illuminant.sp</span><br style="font-family: monospace;">
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<span style="font-family: monospace;"> </span><a
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style="font-family: monospace;" href="#v">-v</a><span
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style="font-family: monospace;">
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Verbose mode</span><span style="font-family:
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monospace;"></span></small><small><span style="font-family:
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monospace;"></span></small><br style="font-family: monospace;">
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<small><span style="font-family: monospace;"></span><span
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style="font-family: monospace;"> </span><a
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style="font-family: monospace;" href="#S">-S</a><span
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style="font-family: monospace;">
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Plot the readings in a graph window.</span><br
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style="font-family: monospace;">
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<span style="font-family: monospace;"> </span><a
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style="font-family: monospace;" href="#c">-c comport</a><span
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style="font-family: monospace;">
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Set
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COM port, 1..4 (default 1)</span><span style="font-family:
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monospace;"></span><span style="font-family: monospace;"></span><span
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style="font-family: monospace;"></span></small><small><span
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style="font-family: monospace;"></span></small><font size="-1"><span
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style="font-family: monospace;"></span></font><font size="-1"><span
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style="font-family: monospace;"><br>
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</span></font><font size="-1"><span style="font-family:
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monospace;"> <a href="#N">-N</a>
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Disable
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initial calibration of instrument</span></font> if possible<br>
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<font size="-1"><span style="font-family: monospace;"> </span><a
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style="font-family: monospace;" href="#H">-H</a><span
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style="font-family: monospace;">
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Use high resolution spectrum mode
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(if available)<br>
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<font size="-1"> <a href="#Yr">-Y r</a>
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Set refresh measurement mode</font><br>
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</span></font><font size="-1"><span style="font-family:
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monospace;"> <a href="#W">-W n|h|x</a>
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Override
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serial port flow control: n = none, h = HW, x = Xon/Xoff</span></font><br>
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<small><span style="font-family: monospace;"> </span><a
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style="font-family: monospace;" href="#T">-T</a><span
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style="font-family: monospace;">
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Test mode - restore & save measurements to<br>
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*_i.sp, *_r.sp, *_p.sp, *_mpir.sp, *_cpir.sp files<br>
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</span></small> <small><span style="font-family: monospace;"> </span><a
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style="font-family: monospace;" href="#D">-D [level]</a><span
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style="font-family: monospace;">
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Print debug diagnostics to stderr</span></small><br>
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<font size="-1"><span style="font-family: monospace;"><a
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href="#file"><span style="font-style: italic;">illuminant.sp</span></a>
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File
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to save measurement to<br style="font-family: monospace;">
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</span></font><small><span style="font-family: monospace;"></span><span
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style="font-family: monospace;"></span></small><br>
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<h3>Usage Details and Discussion</h3>
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<b>illumread</b> uses a suitable instrument to read an illuminant
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spectrum, and uses an indirect method to estimate the Ultra Violet
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content of the illuminant, so as to provide better accuracy with <a
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href="FWA.html">FWA compensation</a>. An instrument or combination
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of instruments capable of spectral measurement of both emissive
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measurement and reflective measurement without a U.V. filter is
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required for this.<br>
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<br>
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<a name="v"></a>The <b>-v</b> flag causes extra information to be
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printed out during chartread operation.<br>
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<br>
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<a name="S"></a>The <b>-S</b> flag enables the plotting of the
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spectral reflectance/transmittance values. You must select the plot
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window and strike a key in it to continue with another measurement.<br>
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<br>
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<a name="c"></a> The instrument is assumed to communicate through a
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USB or serial communication port, and the initial port can be
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selected with the <b>-c</b> option, if the instrument is not
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connected to the first port. If you invoke <span
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style="font-weight: bold;">illumread</span> so as to display the
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usage information (i.e. "illumread -?" or "illumread --"), then the
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discovered USB and serial ports will be listed. On UNIX/Linux, a
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list of all possible serial ports are shown, but not all of them may
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actually be present on your system.<br>
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<br>
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<a name="N"></a><span style="font-weight: bold;">-N</span> Any
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instrument that requires regular calibration will ask for
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calibration on initial start-up. Sometimes this can be awkward if
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the instrument is being mounted in some sort of measuring jig, or
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annoying if several sets of readings are being taken in quick
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succession. The -<span style="font-weight: bold;">N</span>
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suppresses this initial calibration if a valid and not timed out
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previous calibration is recorded in the instrument or on the host
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computer. It is advisable to only use this option on the second and
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subsequent measurements in a single session.<br>
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<br>
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<a name="H"></a> The -<span style="font-weight: bold;">H</span>
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option turns on high resolution spectral mode, if the instrument
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supports it. See <a href="instruments.html">Operation of particular
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instruments</a> for more details.<br>
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<br>
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<a name="Yr"></a> The -<span style="font-weight: bold;">Y r</span>
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option turns on refresh mode measurement, if the instrument supports
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it. This may improve the repeatability of measurements of
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illuminants that have a repetitive flicker.<br>
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<br>
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<a name="W"></a>The <b>-W</b> <span style="font-weight: bold;">n|h|x</span>
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parameter overrides the default serial communications flow control
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setting. The value <span style="font-weight: bold;">n</span> turns
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all flow control off, <span style="font-weight: bold;">h</span>
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sets hardware handshaking, and <span style="font-weight: bold;">x</span>
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sets Xon/Xoff handshaking. This commend may be useful in workaround
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serial communications issues with some systems and cables. <br>
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<br>
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<a name="T"></a>The <b>-T</b> flag invokes the test mode. In test
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mode the three measurements are saved to files <i>illuminant</i><i>_i.sp</i>
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(Illuminant spectrum), <i>illuminant</i><i>_r.sp</i> (Illuminant
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off paper spectrum), and <i>illuminant_p.sp (</i>Instrument
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measured paper reflectance spectrum), and these will be loaded if
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discovered, allowing a replay of the calculation without requiring
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any measurement. In addition, two diagnostic files <i>illuminant</i><i>_mpir.sp</i>
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(Measured paper under illuminant spectrum) and <i>illuminant</i><i>_cpir.sp
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(</i>Computed paper under illuminant spectrum) will be saved.<br>
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<br>
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<a name="D"></a>The <b>-D</b> flag causes communications and other
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instrument diagnostics to be printed to stdout. A level can be set
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between 1 .. 9, that may give progressively more verbose
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information, depending on the instrument. This can be useful in
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tracking down why an instrument can't connect.<br>
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<br>
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<a name="file"></a>The <span style="font-weight: bold; font-style:
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italic;">illuminant.sp</span> is the name of the file to save the
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resulting illuminant spectrum to. The format used is <a
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href="File_Formats.html#.sp">.sp</a>.<br>
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<br>
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<hr style="width: 100%; height: 2px;"><br>
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Unlike the other measurement utilities, <span style="font-weight:
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bold;">illumread</span> doesn't connect to the instrument until it
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is about to make a measurement. This allows for the possibility of
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using a different instrument for each measurement.<br>
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<br>
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It will display a menu:<br>
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<br>
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Press 1 .. 6<br>
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1) Measure direct illuminant<br>
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2) Measure illuminant reflected from paper<br>
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3) Measure paper<br>
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4) Select another instrument, Currently 1 'usb:/bus4/dev2/
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(GretagMacbeth i1 Pro)'<br>
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5) Compute illuminant spectrum, average result with 0 previous
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readings & save it<br>
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6) Compute illuminant spectrum from this reading & save result<br>
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7) Exit<br>
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<br>
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There are three measurements to be made, after which the illuminant
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can be computed and saved. Before each measurement, the instrument
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may need calibrating.<br>
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<br>
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The first measurement needs a spectral instrument capable of reading
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in an ambient or emissive mode. For instance, a Spectrolino, Eye-One
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Pro or ColorMunki would be suitable instruments.<br>
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<br>
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The second measurement needs a spectral instrument capable of
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reading in an projector or emissive mode. For instance, a
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Spectrolino, Eye-One Pro or ColorMunki would be suitable
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instruments.<br>
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<br>
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The third measurement needs a spectral instrument capable of reading
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in reflective mode with UV included. For instance, a Spectrolino,
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Eye-One Pro, DTP20, DTP22 or DTP41 would be suitable
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instruments, as long as they are not fitted with UV filters.<br>
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<br>
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To be able to estimate the level of Ultra Violet (UV) light in the
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illuminant, a reasonable sized piece of white paper needs to be
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used. The paper should have some noticeable level of FWA
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(Fluorescent Whitener Additive, or Optical Brightening Agents) in
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it, so that it responds to UV light. A piece of cheap copier paper
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is ideal, since cheap paper is typically whitened with large amounts
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of FWA. If the paper is thin (less than 160 gsm) then two or three
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sheets should be used to prevent any background showing through. If
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the intention is to use the illuminant spectrum for proofing to a
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particular paper, then it's best to use the intended paper for this
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purpose.<br>
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<br>
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The first measurement <span style="font-weight: bold;">1)</span>,
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is to use either the ambient or emissive measurement mode to measure
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the illumination directly.<br>
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<br>
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<div style="margin-left: 40px;">If the instrument supports an
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ambient measurement capability, then it will be used. If the
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insrument does not have an ambient mode, then an emissive
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measurement mode can be used, although typically many illuminants
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are too bright to directly point the instrument at. A work-around
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is to reflect the illuminant from a spectrally flat white surface.
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A good candidate for this is a piece of white, fine textured
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polystyrene foam, or piece of white <a
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href="https://en.wikipedia.org/wiki/Tyvek">Tyvec</a>. [The
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suitability of a reflector can be checked using <span
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style="font-weight: bold;">spotread -S</span> to check that the
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reflection characteristic is close to flat.]<br>
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<br>
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<img alt="Measuring Ambient" src="illumread_1.jpg" width="143"
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height="272"> <img style="width: 141px; height: 282px;"
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alt="Measuring Ambient" src="illumread_2.jpg"> <img
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style="width: 226px; height: 282px;" alt="Measuring Ambient"
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src="illumread_3.jpg"><br>
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</div>
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<br>
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The second measurement <span style="font-weight: bold;">2)</span>,
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is to measure the illuminant after it has reflected from the paper.<br>
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<br>
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<div style="margin-left: 40px;">This is done by placing the paper
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such that it is uniformly illuminated with reasonable brightness,
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and then placing the instrument so that it receives the reflected
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light from the paper. This is typically achieved by placing the
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instrument close to the paper at about 45º, so that it's aperture
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has a clear view of the illuminated paper, but avoiding shadowing
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the region that is in view, and also avoiding measuring specular
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reflection if the paper is glossy.<br>
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<br>
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<img style="width: 219px; height: 261px;" alt="Measuring via
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Paper" src="illumread_5.jpg"><img style="width: 252px; height:
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259px;" alt="Measuring via Paper" src="illumread_4.jpg"><br>
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</div>
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<br>
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The third measurement <span style="font-weight: bold;">3)</span>,
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is to measure the paper directly using the instrument reflective
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mode measurement.<br>
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<div style="margin-left: 40px;"><img style="width: 186px; height:
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162px;" alt="Measuring Paper" src="illumread_6.jpg"><br>
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</div>
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If a different instrument is needed, use <span style="font-weight:
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bold;">4)</span> to select from the available instruments attached
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to your computer.<br>
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<br>
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Once these three measurements have been made, then the illuminant
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readings spectrum can be computed and save using <span
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style="font-weight: bold;">6)</span>, or a series of readings can
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be made with each reading being averages with the previous readings
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before saving it by using <span style="font-weight: bold;">5)</span>.
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Note that the averaged readings will be weighted by their absolute
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intensities, and that while the direct and indirect illumination
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needs measuring for each reading, the same paper measurement can be
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used each time.<br>
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<br>
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If plotting is enabled, a plot of the measured (black) and with
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estimated UV (red) is plotted. This is followed by a plot showing
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measured paper reflectance (black) and the FWA calculated paper
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reflectance (red).<br>
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<br>
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<br>
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Illumread can then be terminated using <span style="font-weight:
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bold;">7)</span>.<br>
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<h3>References:</h3>
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<p>If For a full description of the approach that illumread uses,
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see:</p>
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<p><b>"Estimating illuminant U.V. without a U.V. capable
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instrument",</b><b><br>
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</b><b>Graeme W. Gill, IS&T 19th Color and Imaging Conference
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Final Program and Proceedings, pp. </b><b><span
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class="pagesNum">58-60(3)</span></b></p>
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<br>
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<br>
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<br>
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<br>
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<br>
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<br>
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<br>
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<br>
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<br>
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<br>
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<br>
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<br>
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</body>
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</html>
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