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 ANALYSIS menu:
 There are two submenus: HISTOGRAM, VALUES.
     
     HISTOGRAM submenu.  If there is an OPEN IMAGE (FILE menu)
 on the screen, and a particle has been BLOCK SELECTed (IMAGE menu),
 then the HISTOGRAM submenu of the ANALYSIS menu displays
 a bar graph of the gray values in the particle.
 The RED BARs represent the distribution of gray values.
 The BLUE BAR is the arithmetic mean for the distribution
 of gray values.  The YELLOW BAR is a DIVIDER for a bimodal
 distribution, calculated by dividing the histogram at all
 possible points along the x-axis, and selecting the minimum
 pooled Student t standard deviation.
     
     VALUES submenu.  If there is an OPEN IMAGE (FILE menu)
 on the screen, and a particle has been BLOCK SELECTed (IMAGE menu),
 then the VALUES submenu of the ANALYSIS menu displays
 particle area (AREA), sum of gray values in the particle
 (GRAYSUM), sum of optical densities in the particle
 (DENSESUM), average optical density (DENSEAVG),
 standard deviation of optical density (DENSESTDV),
 least standard error divider (DIVIDER),
 average diameter of the particle (AVGDIAM),
 greatest diameter (MAXDIAM), least diameter (MINDIAM),
 elliptical eccentricity (ECCENT), center-of-gravity
 x-axis (XCENTER) and y-axis (YCENTER), particle
 contour (CONTOUR), fractal dimension (FRACTAL),
 and perimeter (PERIMETER).
     
     The AREA is the number of pixels INSIDE the particle.  GRAYSUM
 is the sum of GRAY_VALUEs inside the particle.  From each GRAY_VALUE,
 the OPTICAL_DENSITY for that point is calculated by the formula:
 OPTICAL_DENSITY=LOG10(255/(255-GRAY_VALUE)),
 with OPTICAL_DENSITY equal zero if GRAY_VALUE equals 255.
 The DENSESUM is the sum of OPTICAL_DENSITY values
 inside the particle.  DENSEAVG equals DENSESUM/AREA,
 and is designated with a BLUE BAR on the HISTOGRAM.
 DENSESTDV is the standard deviation of OPTICAL_DENSITY
 values inside the particle.  If the x-axis of the HISTOGRAM
 is divided at all points, and a Student t pooled standard
 error is calculated for the left and right histograms
 at every point. The minimum pooled standard error
 at the DIVIDER, and designated with a YELLOW BAR
 on the HISTOGRAM.  The MAXDIAM for the particle is
 the (Euclidean) distance between the two most distant
 edge-points.  If the particle is assumed to be an ellipse,
 then: AREA = (pi/4) * MAXDIAM * MINDIAM, and
 ECCENT = MAXDIAM/MINDIAM.  If the particle is assumed
 to be a circle, then: AREA = (pi/4) * AVGDIAM * AVGDIAM.
 PERIMETER is the sum of edge-points of the particle.
 The particle CONTOUR equals PERIMETER/(2*sqrt(pi*AREA)).
 For a perfect circle, the CONTOUR assumes a minimum value
 of one.  The `fractal dimension', s, of a particle is a 
 quantitative measure of complexity along the particle edge.
 s = 1 + lim(d->0) log2((PERIMETER at 2*d)/(PERIMETER at d)),
 for GRIDSIZE=d, as GRIDSIZE approaches 0.  ISAP(c)
 calculates s for GRIDSIZE=1 pixel.
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