Keywords: greg

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## The Blanking Capability

Experimental data are seldom completely sampled. For example, a spectrometer may have a bad channel, an image bad pixels and so on. To handle this problem, GREG includes the notion of Blanking Value. Most GREG data functions handle this blanking value which is defined using command `SET BLANKING Bval Eval`
where Bval is the blanking value and Eval the tolerance for blanked data, necessary because of limited accuracy. Once a blanking value has been defined, all functions liable to handle it effectively use it. The default value can be overridden using the appropriate option `/BLANKING`. However some functions which should do it still do not handle blanked values ; this currently includes `PERSPECTIVE`.

To turn off the blanking value checking, you must specify a negative value for Eval, or simply use the command `SET BLANKING/DEFAULT`.

The blanking value can be used in two different ways :

1. Avoiding bad points in a curve. In this case it is assumed that points with the Y value blanked are meaningless. Note that this feature allows you to plot a complete set of curves in a single operation : you just need to specify a blanked point to separate each curve.
2. Avoiding bad pixels in an image. In this case, pixels with the blanked value are not considered (for example in command `MEAN`)

One command considers both aspects at the same time : this is command `RGMAP/KEEP Blanking_bis`, for which the default blanking is used to check bad pixels and the Blanking_bis value to force pen up between contours (or parts of a single contour).

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