Re: python 2.6: how to modify a PIL image from C without copying forth and back
News123 news...@free.fr wrote: Yes, this might be an option Somehow though it didn't feel right for me to depend on internal non documented data types, which might change between releases of PIL. That's absolutely true. If performance is a priority, somethimes you have to do things that are dirty. Just include lots of comments saying what you did and why. Personally, because so much of PIL is in C, I would judge internal changes to be unlikely. -- Tim Roberts, t...@probo.com Providenza Boekelheide, Inc. -- http://mail.python.org/mailman/listinfo/python-list
Re: python 2.6: how to modify a PIL image from C without copying forth and back
Hi Tim, Tim Roberts wrote: News123 news...@free.fr wrote: 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? If it were me, I'd be tempted to go peek at the source code for PIL, then pass the Image object to my C routine and poke at the innards to find the buffer with the pixels. Yes, this might be an option Somehow though it didn't feel right for me to depend on internal non documented data types, which might change between releases of PIL. N -- http://mail.python.org/mailman/listinfo/python-list
Re: python 2.6: how to modify a PIL image from C without copying forth and back
News123, 03.03.2010 01:38: 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? Take a look at Cython instead, it will allow you to access PIL's image buffer directly, instead of copying the data. It will also simplify and speed up your C wrapper code. Stefan -- http://mail.python.org/mailman/listinfo/python-list
Re: python 2.6: how to modify a PIL image from C without copying forth and back
Hi Stefan, Stefan Behnel wrote: News123, 03.03.2010 01:38: 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? Take a look at Cython instead, it will allow you to access PIL's image buffer directly, instead of copying the data. It will also simplify and speed up your C wrapper code. Stefan I don't know Cython. Having looked at the web site I'm not entirely sure, I understood your suggestion. Do you mean - to stay with Python 2.6 and to implement only my extension in Cython. This might be very attractive. If yes, can you recommend some url's / tutorials / etc. which might help to implement a cython extension for python2.6. which reads and modifies a pixel of a PIL image. or do you mean - to switch entirely from Python 2.6 to Cython. I would be reluctant to do so, as I have already a lot of existing code. and I do not have the time to check the entire code base for portability issues thanks in advance N -- http://mail.python.org/mailman/listinfo/python-list
Re: python 2.6: how to modify a PIL image from C without copying forth and back
News123, 03.03.2010 10:37: Stefan Behnel wrote: Take a look at Cython instead, it will allow you to access PIL's image buffer directly, instead of copying the data. It will also simplify and speed up your C wrapper code. I don't know Cython. Having looked at the web site I'm not entirely sure, I understood your suggestion. Do you mean - to stay with Python 2.6 and to implement only my extension in Cython. Absolutely. This might be very attractive. If yes, can you recommend some url's / tutorials / etc. which might help to implement a cython extension for python2.6. which reads and modifies a pixel of a PIL image. Check out the tutorial on the web site, and ask on the cython-users mailing list about integration with PIL. I'm sure you'll get some useful examples. Here's something closely related, although it doesn't really use PIL (but the mechanisms are the same): http://wiki.cython.org/examples/mandelbrot or do you mean - to switch entirely from Python 2.6 to Cython. I would be reluctant to do so, as I have already a lot of existing code. and I do not have the time to check the entire code base for portability issues The nice thing about Cython is that you always have a normal CPython interpreter running, so you can split your code between the interpreter and the compiler at any level of granularity. However, the advice was really to write your image processing algorithm in Cython, not your entire program. Stefan -- http://mail.python.org/mailman/listinfo/python-list
Re: python 2.6: how to modify a PIL image from C without copying forth and back
News123 news...@free.fr wrote: 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? If it were me, I'd be tempted to go peek at the source code for PIL, then pass the Image object to my C routine and poke at the innards to find the buffer with the pixels. -- Tim Roberts, t...@probo.com Providenza Boekelheide, Inc. -- http://mail.python.org/mailman/listinfo/python-list
