python 2.6: how to modify a PIL image from C without copying forth and back

Le
News123
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
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News123
Le #21303951
Pardonm

Je me suis trompe :-(
J'ais voulu poster dans comp.lang.python.


Voila un petit traduction

News123 wrote:
Bonjour,

J'ais cree un image gris avec PIL.

Avec une fonctione en C ja'aimerais bien de traverser tout le pixel et
modfier quelques uns.


Pour l'instance je fais:
- transformer l'image en string()
- creear un array('B') avec la bonne taill poru l resultat.
- appeler ma fonctione C, qui fairas une copie d'image entier pour modifier quelques pixels apres.



Est-ceq ue on peut arriver de faire la meme manipulation sans le copy?


########## Python code snippet ################

im = Image.open('grayscalefile_onebyteperpixel')
wx,wy = im.size

# creer un string pour le passer a ma fonctionne
im_as_string = im.tostring()

# creer a array pour stocker le resultat
new_img_array = array.array('B', [0]*(wx*wy) )


my_extension.my_func(wx,wy,im_as_string,new_img_array)


im = Image.frombuffer('L',(wx,wy),new_img_array)
show(im)

############ 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);


Merci beaucoup pour votre idees


bye


N






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.


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