<?php
/*
Plugin Name: Sharpen Resized Images
Plugin URI: http://unsalkorkmaz.com/ajx-sharpen-resized-images/
Description: This plugin sharpening resized jpg image uploads in your WordPress. No settings required.
Author: Ünsal Korkmaz
Author URI: http://unsalkorkmaz.com/
Version: 1.4
License: GPL v3

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/ 

/*
filter usage:
	add_filter('sharpen_resized_corner',function(){ return -1.2; });
	add_filter('sharpen_resized_side',function(){ return -1; });
	add_filter('sharpen_resized_center',function(){ return 20; });
*/
function ajx_sharpen_resized_files( $resized_file ) {
	
	$image = imagecreatefromstring( file_get_contents( $resized_file ) );
	
	$size = @getimagesize( $resized_file );
	if ( !$size )
		return new WP_Error('invalid_image', __('Could not read image size'), $file);
	list($orig_w, $orig_h, $orig_type) = $size;

	switch ( $orig_type ) {
		case IMAGETYPE_JPEG:
			$matrix = array(
				array(apply_filters('sharpen_resized_corner',-1.2), apply_filters('sharpen_resized_side',-1), apply_filters('sharpen_resized_corner',-1.2)),
				array(apply_filters('sharpen_resized_side',-1), apply_filters('sharpen_resized_center',20), apply_filters('sharpen_resized_side',-1)),
				array(apply_filters('sharpen_resized_corner',-1.2), apply_filters('sharpen_resized_side',-1), apply_filters('sharpen_resized_corner',-1.2)),
			);

			$divisor = array_sum(array_map('array_sum', $matrix));
			$offset = 0; 
			imageconvolution($image, $matrix, $divisor, $offset);
			imagejpeg($image, $resized_file,apply_filters( 'jpeg_quality', 90, 'edit_image' ));
			break;
		case IMAGETYPE_PNG:
			return $resized_file;
		case IMAGETYPE_GIF:
			return $resized_file;
	}	
	
	// we don't need images in memory anymore
	imagedestroy( $image );
	
	return $resized_file;
}	
	
add_filter('image_make_intermediate_size', 'ajx_sharpen_resized_files',900);