FIFTH CANADIAN CONFERENCE ON NONDESTRUCTIVE ... - IAEA

CONTRAST (Continued)
NO. 1 PARALLEL LINES:
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Once the slope or line is drawn, any one of the following
three methods may be used to produce the same answer
{*_ 5%). The following graphs demonstrate each method.
In the lower right hand corner of the graph paper, there is a slash line or
a full line at a 45 angle that intercepts the density scale at D 1.00.
Using parallel rulers, opposing triangles or by measuring with a ruler, move
the H&D average gradient slope line over so that it intersects with the slash
reference line at the bottom of the graph paper. Project the line upward; where
it meets the vertical rise of numbers, read the number as the contrast value.
As you can easily see the rise in numbers stops too soon. By measurement, the
vertical scale can easily be extended. Another method would be to cut out a
portion of graph paper and make a scale extender. Another approach is to change
the density scale readings. To do this move the parallel slope line to the
right, just past Step 19. Draw a 45 angle and line so that it exactly meets
D 0.50 on the vertical rise. Relabel this as 1.00; 1.00 becomes 2.00, etc. The
scale has been doubled.
NO. 2 TANGENT OP THE ANGLE:
Using a protractor read the angle of the incline or slope (H&D average gradient
line) to the half or quarter of a degree, if possible. Look up the
tangent of that angle in the trignometric functions of a mathematics book or
use a scientific calculator. The answer is the contrast value.
NO. 3 Y OVER X:
This is also called X into Y or "Rise (Y) over Run (X)". From the upper
coordinate (Y) of the average gradient slope line, draw a vertical line down,
very straight and parallel. From the lower coordinate (X) draw a line horizontal
to the right very straight and parallel. Where they intersect should
be a 90 angle. Measure the vertical Y axis in centimeters. Measure the
horizontal X axis in centimeters and divide into the Y value. The answer is
the contrast value.
It is only necessary to perform one of these methods; the one method you
prefer. There are, also, other methods such as the difference in relative
log exposure divided into the density difference range of 2.00.
WEJM/daw