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Fwd: ANN: EpegWrapper: Wraps the epeg library for very fast JPEG thumbna


From: Alex Perez
Subject: Fwd: ANN: EpegWrapper: Wraps the epeg library for very fast JPEG thumbnail generation
Date: Sun, 18 Jan 2004 16:49:57 -0800



Begin forwarded message:

From: Marc Liyanage <address@hidden>
Date: January 18, 2004 3:53:34 PM PST
To: Cocoa Development <address@hidden>
Cc: address@hidden
Subject: ANN: EpegWrapper: Wraps the epeg library for very fast JPEG thumbnail generation

Carsten Haitzler ("rasterman" of Enlightenment fame) wrote a cool little library called "epeg" for very fast JPEG image thumbnail generation.

He writes:

Over the last few days I have addressed something that bothered me greatly while fixing up my web pages. The INSANELY SLOWspeed of generating thumbnails for photos.

First, some background. I have a large photo collection. Definitely not the biggest as I can imagine some people have even more extensive collections. I have something like 1300 photos, most of which are 2560x1920 in size. By any stretch this isn't small. When making thumbnails of these images, under Nautilus on my machine the process would take about 1 second per photo. That's a lot of time to thumbnail my collection. Yes they get cached, but every time you rename or move files around they need re-thumbnailing. This really got to me. So I started using Imlib2 for thumbnailing. Great. This gave about a 2-3 times speedup, letting me do about 2 to 3 thumbnails per second. But that just wasn't good enough. I knew I could do better, thus my work on what I now call Epeg was born.

Epeg can thumbnail at about 25 thumbnails per second. Compared to the original speed of Nautilus... this is a decent speedup and worth the effort of using Epeg. Epeg is a library with a small API that lets you load a JPEG file, scale it down (on load) append comments and thumbnail info, save, access the scaled pixel data, load comments and thumbnail info etc. It's small, compact and fast and it's only requirement is libjpeg.


I used this in a project and created a very simple Objective-C wrapper class which takes a JPEG file path, a bounding box and returns an NSImage instance:

#import "Epeg/EpegWrapperPublic.h"

+ (NSImage *)imageWithPath:(NSString *)path boundingBox:(NSSize)boundingBox {

This will scale down the image proportionally so it fits into the given bounding box, i.e. it will never squeeze the image.



It really is quite fast... It works by skipping over most of the information in the JPEG data which will not be used anyway in the case of a thumbnail:

It makes use of libjpeg features of being able to load an image by only deocding the DCT coefficients needed to reconstruct an image of the size
desired. This gives a massive speedup.


You can download the wrapper class stuff at

    http://www2.entropy.ch/download/Epeg.zip


The original library is at

    http://www.rasterman.com/code.html




_________________________________________________________________
Marc Liyanage                                  address@hidden
                                           http://www.entropy.ch
                                          iChat: address@hidden

                                     Yoda I am. Grammar I can't.
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Alex Perez
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