{"id":421,"date":"2015-03-04T13:47:22","date_gmt":"2015-03-04T13:47:22","guid":{"rendered":"http:\/\/ahay.org\/blog\/?p=421"},"modified":"2016-02-26T13:31:12","modified_gmt":"2016-02-26T13:31:12","slug":"program-of-the-month-sfgrey","status":"publish","type":"post","link":"https:\/\/ahay.org\/blog\/2015\/03\/04\/program-of-the-month-sfgrey\/","title":{"rendered":"Program of the month: sfgrey"},"content":{"rendered":"

sfgrey<\/a> is the most widely used program<\/a> in Madagascar. It is used for plotting multidimensional images with grayscale or pseudocolor. <\/p>\n

sfgrey<\/strong> shares many of its options with other plotting programs, such as sfgraph<\/a>, sfwiggle<\/a>, and sfcontour<\/a>. You can look for common options by running sfdoc stdplot<\/strong> or checking out stdplot documentation<\/a> online. <\/p>\n

Parameters that control the range of data to be displayed are clip=<\/strong>, pclip=<\/strong>, bias=<\/strong>, allpos=<\/strong>, mean=<\/strong>. The default behavior is pclip=99<\/strong>, which means that data values get clipped to the 99-nth percentile. To display values without clipping, use pclip=100<\/strong>. Setting the clip value with clip=<\/strong> takes the precedence over setting the percentage clip with pclip=<\/strong>. The bias=<\/strong> defines the data value for the middle of the color scale range, the default (appropriate for seismic data) is bias=0<\/strong>. When displaying values that are all larger than the bias value, set allpos=y<\/strong> (all positive). To set the bias to the mean value of the data without specifying it explicitly, use mean=y<\/strong>. The following example from trip\/asg\/project<\/a> uses mean=y<\/strong> to display a synthetic model. <\/p>\n

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The gpow=<\/strong> parameter applies a nonlinear scaling by taking the image to the corresponding power. If the value of gpow<\/strong> is less than zero, the appropriate value is estimated from the data. The following example from gee\/pch\/ida<\/a> uses the value of gpow=0.25<\/strong>.<\/p>\n

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If the input is a 3-D cube, sfgrey can use a particular panel (2-D slice) to estimate clip or glow. The panel is specified by gainpanel=<\/strong> and set by default to the first non-zero panel. To estimate clip using the whole cube, specify gainpanel=all<\/strong>. To clip each panel individually, use gainpanel=each<\/strong>. To add a scale bar, specify scalebar=y<\/strong>. By default, the scale bar is vertical. You can make it horizontal by using bartype=h<\/strong>. To set the minimum and maximum values on the scalebar, use minval=<\/strong> and maxval=<\/strong>. To make the scale bar run in reverse, use barreverse=y<\/strong>. The following example from tccs\/optapert\/sigsbee<\/a> uses bartype=h minval=0 maxval=1<\/strong>. <\/p>\n

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By default, sfgrey<\/strong> displays the first axis running vertical from top to bottom, which corresponds to transp=y yreverse=y<\/strong> and is a common way to display seismic data. For other kinds of data, you can modify the default behavior by setting transp=<\/strong>, xreverse=<\/strong>, and yreverse=<\/strong>. The following example from geo391\/hw5\/pocs<\/a> displays a seismic horizon using transp=y yreverse=n<\/strong>. <\/p>\n

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For an explanation of different color schemes (specified with color=<\/strong> parameter), please refer to previous posts: <\/p>\n