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 <liyanage...>
http://www.entropy.ch
iChat: <liyanage...>
Yoda I am. Grammar I can't.
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