Ask Ben: CFImage And Dynamic Image Compression With File Size Limits 

<!--- Param form variables. --->
<cfparam name="form.upload" type="string" default="" />
 
<!--- Check to see if the form was uploaded. --->
<cfif len( form.upload )>
 
	<!--- Upload the photo to a temp directory. --->
	<cffile
		result="upload"
		action="upload"
		filefield="upload"
		destination="#expandPath( './' )#"
		nameconflict="makeunique"
		/>
 
	<!---
		Read the image from the temp directory so that we
		can resize it to fit in the given area.
	--->
	<cfimage
		name="photo"
		action="read"
		source="./#upload.serverFile#"
		/>
 
	<!--- Resize the image to fit in the specified box. --->
	<cfset imageScaleToFit(
		photo,
		500,
		500
		) />
 
 
	<!---
		Now that we have our resized image, we need to write it
		to disk. Because we want to impose a file size limit,
		we are going to keep trying to save the image until we
		have a decent file size.
	--->
 
	<!---
		Start out with 95% quality. The reason that we are not
		starting out with full quality is that 100% usually
		creates a file that is *surprisingly large*.
	--->
	<cfset imageQuality = 0.95 />
 
	<!--- Set the max file size. --->
	<cfset maxFileSize = (60 * 1024) />
 
	<!--- Set the name of the resized image file. --->
	<cfset photoFile = (
		upload.serverFileName &
		"-resized." &
		upload.serverFileExt
		) />
 
 
	<!--- Keep track of the number of iterations. --->
	<cfset saveCount = 0 />
 
	<!--- Start image save loop. --->
	<cfloop condition="true">
 
		<!---
			Write the image to the disk with the current level
			of compression.
		--->
		<cfimage
			action="write"
			source="#photo#"
			destination="./#photoFile#"
			quality="#imageQuality#"
			overwrite="true"
			/>
 
		<!--- Increment the save count. --->
		<cfset saveCount++ />
 
		<!--- Get the file size of the new image file. --->
		<cfset fileSize = getFileInfo(
			ExpandPath( "./#photoFile#" )
			).size
			/>
 
 
		<!---
			Check to see if the file size is greater than the
			target file size. If it is not, then we need to
			decrease the photo quality and try again.
		--->
		<cfif (fileSize gt maxFileSize)>
 
			<!--- Reduce the quality by 5%. --->
			<cfset imageQuality -= .05 />
 
		<cfelse>
 
			<!---
				The file size is fine, so just break out of
				the loop.
			--->
			<cfbreak />
 
		</cfif>
 
	</cfloop>
 
</cfif>
 
 
<cfoutput>
 
	<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
	<html>
	<head>
		<title>CFImage Dynamic Compression Demo</title>
	</head>
	<body>
 
		<h1>
			CFImage Dynamic Compression Demo
		</h1>
 
		<form
			action="#cgi.script_name#"
			method="post"
			enctype="multipart/form-data">
 
			<p>
				<input type="file" name="upload" size="40" />
			</p>
 
			<p>
				<input type="submit" value="Upload Photo" />
			</p>
 
		</form>
 
 
		<!--- Check to see if we have an upload photo. --->
		<cfif structKeyExists( variables, "photo" )>
 
			<h2>
				Resized Image<br />
 
				<!--- Image properties. --->
				Size: #numberFormat( fileSize, "," )#
				(Max: #numberFormat( maxFileSize, "," )#)<br />
 
				Quality: #imageQuality#<br />
				Iterations: #saveCount#
			</h2>
 
			<p>
				<img src="./#photoFile#" />
			</p>
 
		</cfif>
 
	</body>
	</html>
 
</cfoutput>

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