PNG Compression

[marc_gfx]

I am using Imagick to resize uploaded images. I have noticed that a large PNG24 I uploaded (2000*2249 pixels at 208kb) increases in size after resizing. The goal of resizing is really to reduce the load on the server

The new values are 1024*910 pixels at 460kb. So for a quarter of the pixels it uses more than double the amount of file space.

I compared this to compression done with photoshop6 and it reduces the image to ~152kb, so something must be going wrong. I assume there are options I have not found yet?

I have tried $im->setCompression (Imagick::COMPRESSION_ZIP) with no change in the result.

[marc_gfx]

I found a solution in the forum (I thought). But it wont work probably because of this:

There seems to be a slight problem with setting image or channel depth. Using Q16, setting the depth to 8 bit, you will have a 16 bit file.
Doesn't matter with better previews / image processing programs. With Win systems the display for TIFF files is a kind of psychedelic art.
This took me hours until I did check with PhotoShop. Besides: even if it works with RGB and PNG files, this consumes resources. Have a look on file size.
Only way out: change to Q8.
IMHO there is no way to run Q8 and Q16 simultaneously.
The above said concerns also setImageDepth.

is there a disadvantage if I use Q8? or does it make more sense anyway for websites?

[marc_gfx]

I will continue to answer my own questions ... I have installed Q8 and the PNG file is now 130kb after resizing. I guess Imagick Q16 has a little bug in the setImageDepth function (in the version I have).

[vitty]

Hello,

I have a simmilar problem as above.

source file: 24-bits per pixel RGB image (each channel 8-bits per pixel)
I use the scale method for resizing images and then I write the image to the disk.
output file: 48-bits per pixel RGB (each channel 8-bits per pixel)

This happens for PNG files. (not JPG files)
If I use setImageDepth(8) then it doesn't change the output depth (still 16). The output PNG files are so big because 16-bit output.

This looks like a bug.

Linux OS
ImageMagick version ImageMagick 6.3.8 01/30/08 Q16
imagick module version 2.0.1

Thanks for help

[mkoppanen]

Can you post code and example images? I can not reproduce this issue.

I am running ImageMagick 6.4.2.

[vitty]

Hi,

below is the code and I've attached test images.

Code: Select all

$im_handler = new Imagick();
$im_handler->readImage( '/var/www/html/test/png/input.png' );
$im_handler->scaleImage( 640, 512 );
$im_handler->writeImage( '/var/www/html/test/png/output.png' );
$im_handler->destroy(); 

$im_handler_2 = new Imagick();
$im_handler_2->readImage( '/var/www/html/test/png/input.png' );
$im_handler_2->scaleImage( 640, 512 );
$im_handler_2->setImageDepth( 8 );
$im_handler_2->writeImage( '/var/www/html/test/png/output_2.png' );
$im_handler_2->destroy(); 

exec("/opt/ImageMagick/bin/convert \"/var/www/html/test/png/input.png\" -scale 640x512 -depth 8 \"/var/www/html/test/png/output_3.png\"",$output);

Linux OS
ImageMagick version ImageMagick 6.3.8 01/30/08 Q16
imagick module version 2.0.1

[vitty]

another two output images

[mkoppanen]

Hi,

unable to reproduce with ImageMagick 6.4.2. I will try with older version at some point.

[vitty]

Hi,

unable to reproduce with ImageMagick 6.4.2. I will try with older version at some point.

Hi

it means that the problem is fixed in the newest version of imagick and image magick?

[mkoppanen]

Can you try it with newer version? You can use ./configure --prefix=/opt/imagemagick_new or something similar so it won't mess your current installation.

[colnector]

Optipng could be useful to optimize the resulting files anyway