Re: GD library and PHP

Dmitry, Sorry, for the length of my reply, and now the fact that I'm just refferring you to another source. I'm actually not responsible for the gd library (at least since I last checked :). Your help would definitely be appreciated, I've forwarded this request to php-dev@lists.php.net which is the developers mailing list. If you would like to work on the gd extension, please feel free to apply for a cvs account at: http://www.php.net/cvs-php.php Thanks, Sterling > Hello, > > I have recently learned that GD library is being integrated into > PHP, and apparently you have some relation to that. > > While GD library has a very good set of functions, the > implementation is very poor in my opinion. The code is quite > redundant and un-optimized in any way. This probably has to be > addressed to the author of GD, but since it is now going to be > part of PHP, may be some apparent optimization can be applied to > the bundled version. > > My concerns raised when I tried to use ImageCopyResampled > function. It nearly brings my server to its knees due to high > memory and processor usage (when running 15-20 Apache processes > each processing some image via ImageCopyResampled in PHP). The > processing time is also very high - typically around 10 seconds > for 1 calls to ImageCopyResampled with 1-2 megapixel images. > > Of course, those numbers relate to my server, people with faster > computers may get better results. > > By in any case, I decided to look into implementation of > gdImageCopyResampled in GD library and saw lots of this that can > be improved. I did not look into other function, but I suspect > this is true for the whole GD library. > > The function uses brute force approach and many values that can > be calculated in the outer loop or outside of any loops are > being calculated in the inner loop. E.g. > > sy1 = ((float) y - (float) dstY) * (float) srcH / (float) dstH; > sy2 = ((float) (y + 1) - (float) dstY) * (float) srcH / (float) dstH; > is being calculated for each x, while it really needs to be calculated for each y. > > This part is a constant: > > (float) dstY * (float) srcH / (float) dstH > > and therefore can be calculated once per call, not dstW*dstH*2 times. > > Similarly, > > int pd = gdImageGetPixel (dst, x, y); > > is being called inside of the inner loop (dstW*dstH times!) = but > is not being used anywhere later! > > Applying some apparent mathematics, we can calculate the final > spixels value in one easy step, rather than using (potentially) > multiple floating point additions and multiplications in the inner loop (spixels > += xportion * yportion). Instead total spixels value for the current (x,y) can be found as > > spixels = (y2-y1)* (x2-x1); // and, again, this can also be optimized further > > I can point out several other things that can be easily improved, but you got my point already. > > It is possible to reduce number of calculation dramatically, without breaking readability > and/or > compatibility. > > I am wondering if anyone is considering to do this any time soon. I would be more than willing > to discuss my suggestions with someone responsible for this library, or even modify the code > myself (a little bit harder for me, since I have little time to make extensive tests). > > Regards, > Dmitry > > -- > Dmitry Petrov > phone: (212) 641-3235 > pager: pagedp@nchcapital.com > > > -- > > *** DISCLAIMER *** > > This message is intended only for the use of the individual > or entity to which it is addressed and may contain information > that is privileged, confidential and exempt from disclosure > under applicable law. If the reader of this message is not > the intended recipient or the employee or agent responsible > for delivering the message to the intended recipient, you are > hereby notified that any dissemination, distribution or copying > of this communication is strictly prohibited. If you have received > this message in error, please notify the sender by reply > transmission and delete the message. > ------------------ > >