
Viewimage(Display Utils)     Khoros      Viewimage(Display Utils)

     Threshold/Windowing

     This subform allows the user to perform pixel thresholding
     and/or pixel windowing operations.

     1)  Pixel Windowing

     Pixel windowing is used to mask out certain parts of the
     image so that only a desired range of pixels is observed.
     Pixel windowing works by allowing a windowed region of the
     original pixel values to be displayed.  The user selects the
     pixel value of the masked region; all values outside the
     windowed region will be set to this masked region pixel
     value. If the masked region pixel value does not exist in
     the colormap, the corresponding grey level value will be
     used.

     In order to make sure that none if the other editimage
     features (specifically, pseudocolor or lut) over-ride this
     threshold, we set the pixel's histogram to zero.  None of
     the other editimage features will be able to update these
     pixels with new values, until the histogram is restored.

     a)  Use of the Scroll Bars with Pixel Windowing
          The desired range of pixels to be observed is set using
          the scroll bars that appear at the bottom of the
          Threshold/Windowing subform. The top scroll bar sets
          the lower end of the desired pixel range;  the bottom
          scroll bar sets the upper end of the desired pixel
          range.  The value boxes to the right of each scroll bar
          displays the values to which the lower and upper pixels
          of the range are set.

     b)  The Masked Region Pixel Value
          This is the pixel value used in the masked regions.

     c)  The Windowed Region - accept/reject
          If the windowed region is set to "accept", the original
          pixel values between the values set by the lower scroll
          bar and the upper scroll bar will be displayed;  this
          can be thought of as a bandpass filter.  If the win-
          dowed region is set to "reject",  the original pixel
          values outside the region defined by the lower and
          upper scroll bars will be displayed; this can be
          thought of as a bandreject filter.

     d)  The Color Strip
          The color strip above the scroll bars displays the
          region windowed and masked, based on the lower and
          upper scroll bar positions.

     2)  Pixel Thresholding

     Pixel thresholding is used to perform real-time image thres-
     holding.  It generates a binary (or 2 pixel value) image.
     Pixel thresholding works by assigning a non-zero pixel value
     to the selected region; the rest of the image will be turned
     black.

     a)  Use of the Scroll Bars with Pixel Thresholding
          The desired range of pixels to be thresholded is set
          using the scroll bars that appear at the bottom of the
          Threshold/Windowing subform. The top scroll bar sets
          the lower end of the desired pixel range;  the bottom
          scroll bar sets the upper end of the desired pixel
          range.  The value boxes to the right of each scroll bar
          displays the values to which the lower and upper pixels
          of the range are set.

     b)  The Non-Zero Pixel Value
          This is the pixel value assigned to the all the pixels
          within the range defined by the scroll bars.  Note that
          pixels outside this range will appear black.

     c)  The Threshold Region - non-inverted/inverted
          If the threshold region is set to "non-inverted", the
          non-zero pixel value will be displayed between the lim-
          its set by the lower scroll bar and the upper scroll
          bar;  the rest of the image will be black.  If the
          threshold region is set to "inverted",  the non-zero
          pixel value will be displayed outside the limits set by
          the lower scroll bar and the upper scroll bar.

     d)  The Color Strip
          The color strip above the scroll bars displays the
          thresholded region based on the lower and upper scroll
          bar positions.

     Reset

     Clicking on the "RESET" button will re-set the currently
     displayed image to it's original state when the
     Windowing/Thresholding subform was entered for the first
     time.

     Copyright 1992, University of New Mexico. All rights
     reserved.

Khoros                    Release: 1.0                          1

