I have a camera which has a motor attached which I can rotate using a serial cable. I figured it would be fun to have this camera analyze the webcam shots and turn in any direction there was motion. I pulled out python and pygame, and created a prototype. Unfortunately, I can’t make python go very fast. I made two test cases, 1 in C and 1 in python, to figure out if it would be worthwhile to rewrite it:

array-speed-test.c

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <sys/time.h>

void compare_arrays(int **screen1, int **screen2)
{
    int x;
    int y;
    int diff;
    int mult;

    for(x = 0; x < 1920; x++) {
        for(y = 0; y < 1080; y++)
        {
            mult = screen1[x][y] * screen2[x][y];
            diff = abs(screen1[x][y] - screen2[x][y]);
        }
    }
}

int main(int argc, char **argv)
{
    srand(time(NULL));
    printf("Generating arrays...\n");
    int **screen1;
    int **screen2;
    int i = 0;
    int j = 0;
    struct timeval now;
    struct timeval end;
    int usecs_passed;

    screen1 = malloc(1920 * sizeof(int *));
    screen2 = malloc(1920 * sizeof(int *));
    for(i = 0; i < 1920; i++)
    {
        screen1[i] = malloc(1080 * sizeof(int));
        screen2[i] = malloc(1080 * sizeof(int));
    }

    for(i = 0; i < 1920; i++)
    {
        for(j = 0; j < 1080; j++)
        {
            screen1[i][j] = rand() % 255;
            screen2[i][j] = rand() % 255;
        }
    }

    printf("Comparing arrays...\n");

    gettimeofday(&now, NULL);
    compare_arrays(screen1, screen2);
    gettimeofday(&end, NULL);

    usecs_passed = end.tv_usec - now.tv_usec;

    printf("Time passed: %dms\n", (usecs_passed / 1000));
    for(i = 0; i < 1920; i++)
    {
        free(screen1[i]);
        free(screen2[i]);
    }

    return 0;
}

And my python code:

array-speed-test.py

#!/usr/bin/python
import random
import time
from math import fabs

def generateArray():
    array_to_gen = [None] * 1920
    for i in range(0, 1920):
        array_to_gen[i] = [None] * 1080

    for x in range(0,1920):
        for y in range(0, 1080):
            array_to_gen[x][y] = random.randrange(0,255)

    return array_to_gen

def compareArrays(screen1, screen2):
    for x in range(0, 1920):
        for y in range(0, 1080):
            diff = fabs(screen1[x][y] - screen2[x][y])
            combo = screen1[x][y] * screen2[x][y]

if __name__ == "__main__":
    print "Generating arrays..."
    screen1 = generateArray()
    screen2 = generateArray()

    print "Created two screens.  Comparing..."
    startTime = time.time()
    compareArrays(screen1, screen2)
    print "Time taken: " + str((time.time() - startTime) * 1000) + "ms"

So far, the C program runs in 25ms, while the python program consistently takes 1100ms. Might have to ditch python for real time analysis, unless someone wants to point out how I am doing this completely wrong (I am assuming the comments will be use Numpy?)

Tags: programming, python, sdl