Google PageSpeed & ImageMagick JPG compression - image-processing

Question

Given a user uploaded image, I need to create various thumbnails of it for display on a website. I'm using ImageMagick and trying to make Google PageSpeed happy. Unfortunately, no matter what quality value I specify in the convert command, PageSpeed is still able to suggest compressing the image even further.
Note that http://www.imagemagick.org/script/command-line-options.php?ImageMagick=2khj9jcl1gd12mmiu4lbo9p365#quality mentions:
For the JPEG ... image formats,
quality is 1 [provides the] lowest
image quality and highest compression
....
I actually even tested compressing the image using 1 (it produced an unusable image, though) and PageSpeed still suggests that I can still optimize such image by "losslessly compressing" the image. I don't know how to compress an image any more using ImageMagick. Any suggestions?
Here's a quick way to test what I am talking about:
assert_options(ASSERT_BAIL, TRUE);
// TODO: specify valid image here
$input_filename = 'Dock.jpg';
assert(file_exists($input_filename));
$qualities = array('100', '75', '50', '25', '1');
$geometries = array('100x100', '250x250', '400x400');
foreach($qualities as $quality)
{
echo("<h1>$quality</h1>");
foreach ($geometries as $geometry)
{
$output_filename = "$geometry-$quality.jpg";
$command = "convert -units PixelsPerInch -density 72x72 -quality $quality -resize $geometry $input_filename $output_filename";
$output = array();
$return = 0;
exec($command, $output, $return);
echo('<img src="' . $output_filename . '" />');
assert(file_exists($output_filename));
assert($output === array());
assert($return === 0);
}
echo ('<br/>');
}

Answer 1

The JPEG may contain comments, thumbnails or metadata, which can be removed.
Sometimes it is possible to compress JPEG files more, while keeping the same quality. This is possible if the program which generated the image did not use the optimal algorithm or parameters to compress the image. By recompressing the same data, an optimizer may reduce the image size. This works by using specific Huffman tables for compression.
You may run jpegtran or jpegoptim on your created file, to reduce it further in size.

Answer 2

To minimize the image sizes even more, you should remove all meta data. ImageMagick can do this by adding a -strip to the commandline.
Have you also considered to put your thumbnail images as inline-d base64 encoded data into your HTML?
This can make your web page load much faster (even though the size gets a bit larger), because it saves the browser from running multiple requests for all the image files (the images) which are referenced in the HTML code.
Your HTML code for such an image would look like this:
<IMG SRC="data:image/png;base64,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"
ALT="google" WIDTH=214 HEIGHT=57 VSPACE=5 HSPACE=5 BORDER=0 />
And you would create the base64 encoded image data like this:
base64 -i image.jpg -o image.b64

Answer 3

Google performs those calculations based on it's WebP image format (https://developers.google.com/speed/webp/).
Despite giving performance gains though, it is currently supported only by chrome and opera (http://caniuse.com/webp)