Question

When running Page Speed in Google Chrome it suggests to optimize/compress the images. These images are mostly uploaded by users, so I would need to optimize them during uploading. What I find about optimizing jpeg images with php is something like using the following GD functions:

getimagesize()
imagecreatefromjpeg()
imagejpeg()

Since I am resizing the images after upload I’m already pulling the image through these functions and in addition I use imagecopyresampled() after imagecreatefromjpeg() to resize it.

But then, Page Speed is still telling me these images can be optimized. How can I accomplish this optimisation in a php script? Set the quality lower in imagejpeg() doesn’t make a difference either.

Answer 1

The imagejpeg function is where you assign the quality. If you’re already setting that to an appropriate value then there is little else you can do.

Page speed probably considers all images above a certain size to be “needing compression”, perhaps just ensure they are all as small as reasonable (in terms of height/width) and compressed.

You can find more about page speed and it’s compression suggestions on the pagespeed docs http://code.google.com/speed/page-speed/docs/payload.html#CompressImages which describes some of the techniques/tools to compress appropriately.

I’ve also just read the following:

Several tools are available that perform further, lossless compression on JPEG and PNG files, with no effect on image quality. For JPEG, we recommend jpegtran or jpegoptim (available on Linux only; run with the –strip-all option). For PNG, we recommend OptiPNG or PNGOUT.

So perhaps (if you really want to stick to Google’s suggestions) you could use PHP’s exec to run one of those tools on files as they are uploaded.

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To compress with php you do the following (sounds like you are already doing this):

Where $source_url is the image, $destination_url is where to save and $quality is a number between 1 and 100 choosing how much jpeg compression to use.

function compressImage($source_url, $destination_url, $quality) {
    $info = getimagesize($source_url);

    if ($info['mime'] == 'image/jpeg') $image = imagecreatefromjpeg($source_url);
    elseif ($info['mime'] == 'image/gif') $image = imagecreatefromgif($source_url);
    elseif ($info['mime'] == 'image/png') $image = imagecreatefrompng($source_url);

    //save file
    imagejpeg($image, $destination_url, $quality);

    //return destination file
    return $destination_url;
}