The Multi-Histogram panel displays one or more histograms of image values. The horizontal dimension represents the grey level values from 0 on the left to 255 on the right. The tick marks along the bottom show the 64, 128, and 192 points on the histogram.
The vertical dimension is a representation of the percentage of the pixels in the sample area that have the indicated grey level value. Labels on the left side of the histogram show the maximum percentage representable on the graph. If the top label is "5%", and a spike of the histogram rises to half the height of the graph, then the grey level at that spike represents about 2 1/2% of the sampled area of the image.
The maximum percentage can be controlled by the slider bar beneath the "Maximum Percentage Shown" title bar.
The buttons beneath the "Image Planes" title bar allow the selection of one or more image planes for which histograms will be shown. The histogram title will indicate the image plane and sampling area being displayed.
The "Graphic Mask" area of the panel allows the selection of the sampling area. This can be the area under any of the graphic masks, or just the area of the image that is currently showing in the main image viewing window, or all the data in the image plane.
The histograms on this panel will be updated every time the image data, bitmap masks, or image view windows change. If the "Showing" mask area is chosen, it is possible to roam around the image planes, seeing dynamically how the histograms of different image planes change from area to area.
The statistics are relatively accurate for 8-bit and 16-bit data but are only approximate for 32-bit data. Statistics which are approximate will be indicated by an asterisk (*) on the Statistics panel.
In addition to the above statistics, a larger view of the selected histogram will be displayed. This histogram differs from those on the Multi-Histogram Panel in that it is not always scaled to grey level values from 0 to 255. Instead the histogram displayed will be scaled according to the Data Type of the selected Image Plane.
The "Data Source" area of the panel allows the user to select data source, the minimum and maximum grey levels, and the minimum and maximum occurrence count on the histogram. If the user selects "From Video" then the histogram data will be calculated from the image currently in video; otherwise the histogram data will be calculated from the corresponding image on file.
The user can query the exact pixel count at a certain histogram value by clicking on the histogram at that position with the left mouse button. A message of the form "#### Pixels at value ###" will be displayed.
Due to memory limitation, for 32-bit real data, the histogram will be scaled using a bin size of 64K. This explains why the statistics for 32-bit data are only approximate.
The "Options" area of the panel allows the user to select the output filename, the file format, and the histogram title and labels, and to specify whether or not to print out the statistics.
The "Output Characteristics" area of the panel will vary depending on whether or not the user chooses ASCII or PostScript output. For the ASCII output this area allows the user to set up the minimum and maximum grey levels and the minimum and maximum occurrence count on the histogram. The user can choose to either print out the histogram or the histogram data in ASCII.
For PostScript output, the "Output Characteristics" area of the panel will also allow the user to define the output window on the page.
The "Paper" area of the panel is only available for PostScript output. This area will allow the user to set up the page size, orientation, and number of copies.