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the target response curve actual technical gamma<br>
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<a href="#f">-f [degree]</a>
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Amount of black level accounted for with output offset (default all
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<a href="#a">-a ambient</a>
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Use viewing condition adjustment for ambient in Lux<br>
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</span></font><font size="-1"><span style="font-family: monospace;"> <a
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Use high resolution spectrum mode (if
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</span></font><font size="-1"><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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Use adaptive measurement mode (if available)</span></font><br>
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<font size="-1"><span style="font-family: monospace;"> </span><a
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style="font-family: monospace;" href="#M">-M "command"</a><span
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style="font-family: monospace;">
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Invoke shell "command" each
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target response curve gamma. This is
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normally an exponential curve (output = input ^gamma), and defaults to
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2.4 on MSWindows and Linux/Unix (which is typical for a CRT type
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display), and 1.8 on a Macintosh (OS X). Four pre-defined curves can be
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used as well: the sRGB colorspace response curve, which is an
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2.4 on MSWindows and Macintosh OS X 10.6 or latter and Linux/Unix
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(which is typical of a CRT type
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displays real response), and 1.8 on a Macintosh (prior to OS X 10.6).
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Four pre-defined curves can be
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used as well: the sRGB colorspace response curve, which is an
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exponent curve with a
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straight segment at the dark end and an overall response of
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approximately gamma 2.2 (<span style="font-weight: bold;">-gs</span>),
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and the SMPTE 240M video standard response curve (<span
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style="font-weight: bold;">-g240</span>) <br>
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<span style="font-weight: bold;">Note</span> that a
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real display can't reproduce any of these ideal curves, since it will
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have a non-zero black point, whereas all the ideal curves assume zero
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light at zero input. In the case of a gamma curve target, dispcal uses
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output at 50% input
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as the ideal gamma power curve. To allow for the non-zero black level
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of a real display, by default <span style="font-weight: bold;">dispcal</span>
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will offset and scale the target curve so that zero input gives the
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actual black level of the display (input offset). This ensures the most
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will offset the target curve values so that zero input gives the
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actual black level of the display (output offset). This ensures that
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the target curve better corresponds to the typical natural behavior of
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displays, but it may not be the most
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visually even progression from display minimum, but this behavior can
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be changed using the <span style="font-weight: bold;">-f</span> option
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<span style="font-weight: bold;">Note</span> that many color spaces are
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encoded with, and labelled as having a gamma of approximately 2.2 (ie.
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sRGB, REC 709, SMPTE 240M), but are actually intended to be displayed
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<span style="font-weight: bold;">Also note</span> that many color
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encoded with, and labelled as having a gamma of approximately<span
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style="font-weight: bold;"> 2.2</span> (ie.
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sRGB, REC 709, SMPTE 240M, Macintosh OS X 10.6), but are actually
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intended to be displayed
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on a display with a typical CRT gamma of <span
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style="font-weight: bold;">2.4</span>. This is because this 2.2 gamma
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style="font-weight: bold;">2.4</span> viewed in a darkened
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environment. This is because this <span style="font-weight: bold;">2.2</span>
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is a source gamma encoding in bright viewing conditions such as a
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television studio, while typical display viewing conditions are quite
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dark by comparison, and a contrast expansion of (approx.) gamma 1.1 is
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What you probably want to do, is to set the gamma curve to about gamma
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2.4, so that the contrast range is expanded appropriately, or
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alternatively use sRGB or REC 709 but also use the <span
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style="font-weight: bold;">-a</span> parameter to specify the ambient
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<span style="text-decoration: underline; font-weight: bold;">alternatively</span>
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use sRGB or REC 709 or a gamm of 2.2 but <span
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style="font-weight: bold;">also</span> use the <span
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style="font-weight: bold;">-a</span> parameter to specify the actual
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viewing conditions, so that <span style="font-weight: bold;">dispcal</span>
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can make an appropriate contrast enhancement. If your instrument is
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capable of measuring ambient light levels, then you can do so during
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<http://www.color.org/sRGB.xalter> for details of how sRGB is
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intended to be used.<br>
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It is hard to know whether Apple Macintosh computers should
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It is hard to know whether Apple Macintosh computers prior to OS X 10.6
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also have such an adjustment, since it is not really possible to know
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whether colors labelled as being in such a colorspace are actually
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encoded in that gamma with the expectation that they will be displayed
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style="font-weight: bold;">-G</span> options, real displays do not
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have a zero black response, while all the target response curves do, so
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this has to be allowed for in some way. The default way of handling
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this (equivalent to -f 0) is to offset and scale the input values
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this (equivalent to -f 1.0) is to allow for this at the output of
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response curve, by offsetting and scaling the output values.<span
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style="font-weight: bold;"></span> This defined a curve that will
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responses that many other systems provide and may be a better match to
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the natural response of the display, but will give a
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less visually even response from black<span style="font-weight: bold;"></span>.
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The other alternative is to offset and scale the input values
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into the ideal response
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curve so that zero input gives the actual non-zero display response.
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This ensures the most visually even progression from display minimum.
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The other alternative is to allow for this at the output of the ideal
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response curve, by offsetting and scaling the output values.<span
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style="font-weight: bold;"></span> This can be done by using the <span
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style="font-weight: bold;">-f</span> option. This will probably give a
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less progressive response from black, but may better match the
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responses that other systems provide. A further subtlety is to provide
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This ensures the most visually even progression from display minimum,
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but might be hard to achieve since it is different to the naturally
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response of a display.
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A subtlety is to provide
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a split between how much of the offset is accounted for as input to the
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ideal response curve, and how much is accounted for at the output, and
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this can be done by providing a parameter <span
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style="font-weight: bold;">-f degree</span>, where the degree is 0.0
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accounts for it all as input offset, and 1.0 accounts for all of it as
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output offset. If <span style="font-weight: bold;">-f</span> is used
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without a specified degree, a degree of 0.0 is assumed, the opposite of
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<a name="a"></a><span style="font-weight: bold;">-a ambient</span>: As
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explained for the <span style="font-weight: bold;">-g</span>
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dispcal will attempt to make all colors
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down the neutral axis (R=G=B) have the same hue as the chosen white
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point (equivalent to <span style="font-weight: bold;">-k 1.0</span>).
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point (ie. default is <span style="font-weight: bold;">-k 1.0</span>).
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Near the black point, red, green or blue can only be added, not
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subtracted from zero, so the process of making the near black colors
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have the desired hue, will <span style="font-weight: bold;">lighten</span>
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them to some extent. For a device
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with a good contrast ratio or a black point that has nearly the same
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hue as the white, this is not a problem. If the device contrast ratio
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is not so good, and the black hue is noticeably different to that of
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is not so good, and the native black hue is noticeably different to
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the chosen white point (which is often the case for <span
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style="font-weight: bold;">LCD</span> type displays, or <span
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style="font-weight: bold;">CRT</span> type displays with one channel
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used for <span style="font-weight: bold;">LCD</span>
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type displays, but the <span style="font-weight: bold;">-k</span>
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option allows overriding these with a custom value between 0.0 (no
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correction) to 1.0 (full correction). If less than full correction is
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correction of black) to 1.0 (full correction of black). If less than
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chosen, then the resulting calibration curves will have the target
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white point down most of the curve, but will then blend over to the
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native or compromise black point that is blacker, but not of the right
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hue. The rate of this blend can be controlled with the <span
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style="font-weight: bold;">-A</span> parameter.<br>
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style="font-weight: bold;">-A</span> parameter (see below).<br>
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<a name="A"></a><span style="font-weight: bold;">-A rate</span>:
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If the black point is not being set completely to the same hue as the
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for more details. This may give better accuracy for display
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measurements.<br>
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<a name="V"></a> The -<span style="font-weight: bold;">V</span> option
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uses adaptive emission measurement mode, if the instrument supports it,
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such as the Eye-One Pro. This may give better accuracy for low level
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measurements, but may be more inconsistent overall due to the varying
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integration times. Overall measurement time will probably be longer.<br>
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<a name="M"></a> The -<span style="font-weight: bold;">M</span> <span
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style="font-weight: bold;">"command" </span>option
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allows a method of gathering each test value from some external source,
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doc/dispcal.html
