raspberry pi image cropping very slow

Question

I am currently working on a project to capture and process photos on a raspberry Pi. The photos are 6000X4000 about 2 mb, from a nikon D5200 camera. Everything is working fine, i have made a proof of concept in Java and want to transform this to python or C depending on which language is faster on the raspberry.

No the problem is that the images need to be cropped and re-sized, this takes a very long time in the raspberry. In java the whole process of reading the image, cropping and writing the new image takes about 2 minutes.

I have also tried ImageMagick but in command-line this even takes up to 3 minutes.

With a small python script i made this is reduces to 20 seconds, but this is still a bit to long for my project.

Currently i am installing OpenCV to check if this is faster, this process takes around 4 hours so i thought in the meantime i can ask a question here.

Does anybody have any good idea's or libraries to speed up the process of cropping and re-sizing the images.

Following is the python code i used

import Image

def crop_image(input_image, output_image, start_x, start_y, width, height):
    """Pass input name image, output name image, x coordinate to start croping, y     coordinate to start croping, width to crop, height to crop """
input_img = Image.open(input_image)
box = (start_x, start_y, start_x + width, start_y + height)
output_img = input_img.crop(box)
output_img.save(output_image +".jpg")
def main():
   crop_image("test.jpg","output", 1000, 0, 4000, 4000)

if __name__ == '__main__': main()

Answer 1

First approach (without sprites)

import pyglet
#from pyglet.gl import *

image = pyglet.resource.image('test.jpg')
texture = image.get_texture()
## -- In case you plan on rendering the image, use the following gl set:
#gl.glTexParameteri(gl.GL_TEXTURE_2D, gl.GL_TEXTURE_MAG_FILTER, gl.GL_NEAREST)
texture.width = 1024
texture.height = 768
texture.get_region(256, 192,771, 576)
texture.save('wham.png') # <- To save as JPG again, install PIL

Second attempt (with sprites, unfinished)

import pyglet, time
start = time.time() #DEBUG
texture = pyglet.image.load('test.jpg')
print('Loaded image in',time.time()-start,'sec') #DEBUG
sprite = pyglet.sprite.Sprite(texture)
print('Converted to sprite in',time.time()-start,'sec') #DEBUG
print(sprite.width) #DEBUG
# Gives: 6000
sprite.scale = 0.5
print('Rescaled image in',time.time()-start,'sec') #DEBUG
print(sprite.width) #DEBUG
# Gives: 3000

---

Both solutions end up around 3-5 seconds on an extremely slow PC with a shitty mechanical disk running under Windows XP with.. i can't even count the number of applications running including active virus scans etc.. But note that I can't remember how to save a sprite to disk, you need to access to AbstractImage data container within the sprite to get it out.

You will be heavily limited to your disk/memory-card I/O. My image was 16MB 6000x4000 pixels.. Which i was suprised it whent as fast as 3 seconds to load.

Answer 2

Have you tried jpegtran . It provides for lossless cropping of jpeg. It should be in the libjpeg-progs package. I suspect that decoding the image to crop it, then re-encoding it is too much for the SD card to take.