Aside from the specific implementation of the pixel modification algorithm,
the major difference between this sketch and the sketches since
Pr0120-Image Explorer is that I have
made the code more modular.
For example, I have attempted to isolate those portions of the template that
are likely to change from one algorithm go the next from those portions that areless likely to change. That will make it easier to explain how the code for one
algorithm differs from the code for other algorithms.
The beginning of the
class and the run method
Listing 1 shows the beginning of the class and
the modified
run method. It is unlikely that this code will change much from one algorithm tothe next.
Major differences in the
run method
The first major difference between this and previous versions of the
run method is the delegation of pixel manipulation operations to the method named
processPixels . Moving those operations to a separate method
will decrease the likelihood that it will be necessary to modify the code in
Listing 1 to implement different algorithms.
I will identify the second major change later.
Beginning of the
processPixels method
The
processPixels method, which begins in
Listing 2 , applies a pixel modification algorithm that causes the
green and blue color values to be scaled on a linearbasis moving from left to right across the image.
Does some preliminary housekeeping regarding pixels,
(which you have
seen before) .
Declares local variables for storage of red, green, and blue color
values.
Initializes the counter that is used to position color values in the
output pixel array.
Beginning of a for loop
Listing 3 shows the beginning of a
for loop that is used to process every pixel in the input pixel array.
Get and save color values
The code in
Listing 3 gets and saves the RGB color
values for the current pixel.
Compute the column number
This algorithm applies the same scale factor to every pixel in each column.
Therefore, it is necessary to identify the column to which a pixel belongs whenthe colors for the pixel are retrieved from the pixel array. However, it is not
necessary to identify the row.
(We will get to that in later modules.)
The code in
Listing 4 uses the modulus operator to
compute the column number based on the loop counter,
(which is the same as the input pixel array index) .
Compute the scale
factor for the column
The code in
Listing 4 uses the column number to
compute the two required scale factors.
If case you haven't recognized it, the expression for
greenScale is the equation for a straight line that goes through 1.0 on the left side ofthe image and goes through 0.0 on the right side of the image.