#49696 [Opn->Asn]: PHP GD library can use underlying JPEG library's capability to prescale image

ID: 49696 Updated by: pajoye@php.net Reported By: sriram dot natarajan at gmail dot com -Status: Open +Status: Assigned Bug Type: Feature/Change Request Operating System: unix/linux PHP Version: 5.3SVN-2009-09-28 (snap) -Assigned To: +Assigned To: pajoye New Comment: I have a patch for libgd and jpeglib7 to allow exactly that. However a manual scale is still necessary if you like to have a good result. Previous Comments: ------------------------------------------------------------------------ [2009-09-28 05:03:53] sriram dot natarajan at gmail dot com Description: ------------ GD library is commonly used in PHP5 applications for image processing. When creating thumbnails from a large jpeg image, the original image currently has to be decoded to a full-size copy before being resampled or resized. This is a relatively expensive step. The underlying jpeg library has a capability of prescaling an image when it is being decoded, so for example the decoded image could be only 1/16 the size of the fullsize image by prescaling by a factor of 4. This saves a substantial amount of cpu time. Expected result: ---------------- we can update php libgd library and our php gd extension to leverage underlying jpeg's ability to prescale image at the time of creating jpeg images. for example, we can introduce new API or patch our existing gdImageCreateFromJpeg API to have an extra argument for prescale size so that we can set the value of 'prescale' value like below cinfo.scale_denom = prescale; before calling "jpeg_start_decompress (&cinfo)" function. [credits: thanks to Richard Smith for coming up with this nice suggestion] af course, this will allow users to invoke our 'imagecreatefromjpeg' with an optional argument which specifies the prescale size of this jpeg. $src_img=imagecreatefromjpeg($name, 4); Actual result: -------------- better performance while producing jpeg based thumbnails ------------------------------------------------------------------------ -- Edit this bug report at http://bugs.php.net/?id=49696&edit=1