CODEWITHSUNDEEP
pythonmatrixrgbppm
Alpha24
Alpha24

Reputation: 1

Python - Ppm value RGB in a matrix without library

I'm trying to recover separately value R, G & B from a ppm file in three different matrices.

I wrote this script :

#Read file
feep_file = open("feep.ascii.ppm", "r")

def createMatrixRGB(filename):
    matrixR = []
    matrixG = []
    matrixB = []
    tableR = []
    tableG = []
    tableB = []
    tmp = False
    for lines in filename:
        x = lines.split()
        for y in x:
            if(y == 0 and tmp == False):
                tableR.append(y)
            if(y == 1 and tmp == False):
                tableG.append(y)
            if(y == 2 and tmp == False):
                tableB.append(y)
        tmp = True
    matrixR.append(tableR)
    matrixG.append(tableG)
    matrixB.append(tableB)
    tableR = []
    tableG = []
    tableB = []

    return matrixR, matrixB, matrixG

#Read lines
magic_number = feep_file.readline()
name_file = feep_file.readline()
dimension = feep_file.readline()
k = feep_file.readline()
print(magic_number)
ppm_matrix = createMatrixRGB(feep_file)
feep_file.close()
print(ppm_matrix)

The problem is that I have this result :

P3

([[]], [[]], [[]])

I don't see where I did something wrong. Thanks for your help

Upvotes: 0

Views: 285

Answers (1)

Rotem
Rotem

Reputation: 32144

The main issue is not converting strings to integers, and the usage of y as an index.

Since it's a coding practice, I am not going to just give a solution.
I will try to show you how to use the debugger to find the problem.

Place a breakpoint, run with Debug, and add x and y to the watch:
enter image description here

As you can see, the value of y is '0', and the type is str.

You can also evaluate expressions in the debugger Console (while debugging).
Paste the expression: y == 0 and tmp == False:
enter image description here

As you can see, the expression: y == 0 and tmp == False evaluates to False.
You may run a single step, and notice that the cursor doesn't step to tableR.append(y) (but skip to if(y == 1 and tmp == False)), because the condition is False.

The reason we are getting False is that y == '0', but not 0.

Now evaluate the expression after converting y to int:
int(y) == 0 and tmp == False:
enter image description here

As you can see int(y) == 0 is True.

After all that...
I don't think you have meant to use the value of y.
I think you meant to use the index of y in x.

[Note: Your conventions are wrong - normally y is the line, and x is the position in the line, but I kept your names].

Corrected code (at least partially corrected):

#Read file
feep_file = open("feep.ascii.ppm", "r")

def createMatrixRGB(filename):
    matrixR = []
    matrixG = []
    matrixB = []
    tableR = []
    tableG = []
    tableB = []

    for lines in filename:
        x = lines.split()
        color_index = 0
        for y in x:
            if color_index % 3 == 0:  # Use color_index modulo 3 (like counting 0, 1, 2, 0, 1, 2...)
                tableR.append(int(y))
            if color_index % 3 == 1:
                tableG.append(int(y))
            if color_index % 3 == 2:
                tableB.append(int(y))
            color_index += 1

        matrixR.append(tableR)
        matrixG.append(tableG)
        matrixB.append(tableB)

        tableR = []
        tableG = []
        tableB = []

    return matrixR, matrixB, matrixG

#Read lines
magic_number = feep_file.readline()
name_file = feep_file.readline()
dimension = feep_file.readline()
k = feep_file.readline()
print(magic_number)
ppm_matrix = createMatrixRGB(feep_file)
feep_file.close()
print(ppm_matrix)

Result:

([[0, 0, 0, 15], [0, 0, 0, 0], [0, 0, 0, 0], [15, 0, 0, 0]], [[0, 0, 0, 15], [0, 7, 0, 0], [0, 0, 7, 0], [15, 0, 0, 0]], [[0, 0, 0, 0], [0, 15, 0, 0], [0, 0, 15, 0], [0, 0, 0, 0]])

Upvotes: 1

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