JPEG Compress to target Filesize

jpegfit.php

<?php
/**
 * JpegFit Class
 * 2007-04-12	Image Resource getters and setters with examples
 * 2007-03-29    First Version
 *
 * IMPORTANT NOTE
 * There is no warranty, implied or otherwise with this software.
 *
 * LICENCE
 * This code has been placed in the Public Domain for all to enjoy.
 *
 * @author    Zafar Iqbal <ultrasine@gmail.com>
 * @package   JpegFit
 */
class JpegFit
{
	// Image file path
	private $imageFilePath;

	// Image handle
	private $im;

	// Quality range
	private $low, $high;
	private $q, $cq;

	// Target image size
	private $targetSize;

	// Target resolution
	private $width,$height,$resizeFlag;

	// Precision
	private $precision;

	// Max Iterations
	private $maxIterations;

	// Debug Array
	private $debug;

	// Class Constructor
	public function __construct()
	{
		$this->init();
	}

	// Class Destructor
	public function __destruct()
	{
		imagedestroy($this->im);
	}

	// Init variables
	public function init()
	{
		// Image filename and resource handle
		$this->imageFilePath = NULL;
		$this->im = NULL;

		// Quality range
		$this->low = 0;
		$this->high = 100;
		$this->q = 50;
		$this->cq = 50;

		// Difference in high/low to break loop
		$this->precision = 0.1;

		// Total iterations to break loop
		$this->maxIterations = 16;

		// Default resize flag
		$this->resizeFlag = false;
	}

	// Set function for path to image - can be URL
	public function setImageFilePath($path)
	{
		$this->imageFilePath = $path;
	}

	// Set function for target size - in bytes
	public function setTargetSize($size)
	{
		$this->targetSize = $size;
	}


	// Set width and height for output image (see example 5)
	public function setResolution()
	{
		$args = func_get_args();

		if(count($args) == 0 || count($args)>2) return;

		$this->resizeFlag = true;
		$this->width = $args[0];
		$this->height = $args[1];
	}

	// Set Image Resource
	public function setImageResource($ir)
	{
		$this->im = $ir;
	}

	// Get Image Resource
	public function getImageResource()
	{
		return $this->im;
	}

	// Function to compute jpeg quality setting restricted to image size
	public function fit()
	{
		// Load image
		if($this->im == NULL) $this->im = imagecreatefromstring(file_get_contents($this->imageFilePath));

		if($this->resizeFlag)
		{
			$newWidth = $this->width;
			$newHeight = $this->height;

			$t = imagecreatetruecolor($newWidth,$newHeight);
			imagecopyresampled($t,$this->im,0,0,0,0,$newWidth,$newHeight,imagesx($this->im),imagesy($this->im));
			imagedestroy($this->im);
			$this->im = $t;
			//imagedestroy($t);	
			$this->debug[] = "[RESIZE] TRUE -> $newWidth $newHeight";
		}

		// Counter to keep track of iterations
		$cc = 0;

		// Use the buffer NOT the filesystem to compute intermediate image size
		ob_start();

		// Loop forever
		while(true)
		{
			// Empty buffer
			ob_clean();

			// Keep track of previous quality setting
			$this->cq = $this->q;

			// Create and fill buffer with image with current quality setting
			imagejpeg($this->im, NULL, $this->cq);

			// Compute current image size from size of buffer
			$currentSize = strlen(ob_get_contents());

			// Some debug
			$this->debug[] = " " . $this->low . " >>> " . $this->cq . " <<< " . $this->high . " [ $currentSize / " . $this->targetSize . " ]";

			// Break loop if target size is reached - very rare!
			if ($currentSize == $this->targetSize)
			break;

			// If size > target then change quality range
			if ($currentSize > $this->targetSize)
			{
				$this->high = $this->q;
				$this->q = ($this->q + $this->low) / 2;
			}

			// If size < target then change quality range
			if ($currentSize < $this->targetSize)
			{
				$this->low = $this->q;
				$this->q = ($this->q + $this->high) / 2;
			}

			// Break loop if high/low gap below precision AND size is < target size
			if ((($this->high - $this->low) < $this->precision) && ($currentSize <= $this->targetSize)) break;

			// Break loop of counter has reached maximum iterations - target size either to low/high
			if ($cc == $this->maxIterations) break;

			// Continue loop incrementing counter
			$cc++;
		}

		// Final debug
		$this->debug[] = "Final Quality Setting = " . $this->cq;

		// Disable buffer
		ob_end_clean();
	}

	// Save image to filename
	public function saveImage($filename)
	{
		imagejpeg($this->im, "$filename", $this->cq);
	}

	// Send image to client - including http header
	public function clientOutput()
	{
		header("Content-type: image/jpeg");
		imagejpeg( $this->im, NULL, $this->cq);
	}

	// Get the final quality setting
	public function getQ()
	{
		return $this->cq;
	}

	// Ouput debug that has been generated
	public function dprint()
	{
		print_r($this->debug);
	}
}