Compare treats each point in the top slice of a database as a vector
of length equal to the depth of the database. It does a vector comparison
between the point at the location of the crosshair and each other point
in the database, using one of a variety of vector norms (metrics). It displays
the distance in vector space between each point and the crosshair point,
so low numbered pixels in the final rendering will be vectors close to
the crosshair vector.
Magnify and Minify do the normal things. See Image
for more detail on them.
Compute causes a new rendering to be calculated. If one moves the crosshair
around, the image will not update until the Compute button is pressed.
Normalize forces all vectors to have unit length.
Reverse Color will swap the non-special contents of the color table. (Missing
Data and No Data values are considered to be special.)
The Function menu indicates which vector norm is to be used. The choices
Crosshair puts the application into "Crosshair mode," allowing you to control
the crosshair. It starts in this mode; it is only necessary to do this
if one was using the bounding box. See the
Crosshair section below for more information about the crosshair.
The standard (L-2) vector norm (square root of the sum of the squares of
the differences of the components).
The sum of the squares of the differences in the components. This is the
square of the standard vector norm.
The sum of the absolute values of the difference in the components. (The
L-1 vector norm.)
The sum of the squares of the differences of the components, normalized
by the square of the sum of the reference point and the test point.
The arc cosine of the dot product of the two vectors.
Resize Bounding Box puts the application into "Bounding Box mode," and
allows one to change the size and position of the bounding box. Press the
mouse button somewhere in the image and, holding the mouse button down,
move the mouse to somewhere else in the image. A red rectangle will follow
the mouse. When the mouse button is released, the rectangle will become
a bounding box. See the Bounding Box section below for more about bounding
Move Bounding Box returns Compare into bounding box mode if it wasn't
already and allows the bounding box to be dragged around, but prevents
its size from changing.
Remove Bounding Box is the same as Crosshair.
Inclusive/Exclusive Bounding Box determines whether the bounding box
represents the area inside the bounding box edges, or all the area outside
The crosshair is the little plus-sign shaped icon that starts in the middle
of the image. It can tell Compare or other applications of its position.
Compare's crosshair is used to choose the reference point in vector space
for distance calculation.
The Bounding Box
The bounding box is a representation of a rectangular chunk of the database.
It can tell other applications about its position and size in order to
compute statistical information about the data within the box or to limit
the application only to data within the box.
Bounding boxes can be inclusive or exclusive. Inclusive bounding boxes
represent all the data within the edges of the box; exclusive ones represent
all the data outside the edges of the box. The edges of the box are included
in each case.
Applications to Connect to This Application
Any Data Object may be connected via the
"drag 'n drop" button to this application. If Average,
or Combine is linked into Compare, their crosshairs
or bounding boxes will control Compare's. The Color
Tool will change the palette used in Image without changing the database's
palette. Histogram can be linked in to limit
the palette used in Image.
Applications to Link This Application to
Compare can control Combine, Image
or Average by being linked in and using its
crosshair or bounding box. The crosshair
and bounding box in the application to which Image is linked will follow
Image's in this case.
LinePlot will follow Compare's crosshair
if Compare is linked into it; this is the most common way to use LinePlot.
TrackPixel will use Compare's crosshair and
bounding box to produce statistical information about the database if Compare
is linked into it; this is the most common way to use TrackPixel.
ValueView will indicate which values are
within Compare's bounding box if Image is linked into it.
Tricks and Gotchas
Remember to normalize vectors before using the dot product norm.
/ Oct 5, 2001