News123
3/3/2010 12:38:00 AM
Hi,
I created a grayscale image with PIL.
Now I would like to write a C function, which reads a;most all pixels
and will modify a few of them.
My current approach is:
- transform the image to a string()
- create a byte array huge enough to contain the resulting image
- call my c_function, which copies over the entire image in order
to modify a few pixels
How can I achieve this with the least amount of copies?
########## Python code snippet ################
im = Image.open('grayscalefile_onebyteperpixel')
wx,wy = im.size
# create a string in order to pass it to my function
# I'm afraid this involves copying so want to get rid of it
im_as_string = im.tostring()
# create a byte array in order to store my result
new_img_array = array.array('B', [0]*(wx*wy) )
# my function which should just change some pixels has
# to copy all unmodified pixels
my_extension.my_func(wx,wy,im_as_string,new_img_array)
im = Image.frombuffer('L',(wx,wy),new_img_array)
show(im2)
############ C wrapper code snippet ###############
int wx,wy;
Py_buffer img;
Py_buffer new_img;
Py_buffer table;
unsigned char *img_ptr;
unsigned char *new_img_ptr;
int ok = PyArg_ParseTuple(args,
"iis*w*",&wx,&wy,&img,&new_img);
img_ptr = (unsigned char *) img.buf;
new_img_ptr = (unsigned char *) new_img.buf;
my_func(wx,wy,img_ptr,new_img_ptr);
Thanks in advance for any suggestions to make this more efficient.
bye
N