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Re: iPhoto-like scroll view
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Re: iPhoto-like scroll view


  • Subject: Re: iPhoto-like scroll view
  • From: glenn andreas <email@hidden>
  • Date: Sat, 8 Sep 2007 10:56:29 -0500


On Sep 8, 2007, at 10:43 AM, Chris Williams wrote:

Been there, done that, got the t-shirt :)

Actually, the limiting factor (for me at least) was just schleping the image
in from the disk, and writing it back to the database. Once I had it in
memory, I played with all kinds of techniques to make the thumb and nothing
made much of a difference. So I went with one that was clean and did what I
wanted.


If you think about it, it makes sense. Just copying a folder with several
thousand images, each several hundred K in size, is a slow operation.



That's one of the advantages of CGImageSourceCreateThumbnailAtIndex, though, is that in many cases it doesn't have to read the entire file to generate the thumbnail. For example, many digital cameras embed a thumbnail in the EXIF data of a JPG file, which CGImageSourceCreateThumbnailAtIndex can use, allowing for it to only have to scan in the first couple of K of a file instead of reading the entire several hundred K. Similar tricks can be done with progressive jpg files (again just reading the first couple of low resolution passes, and not the full resolution) and JPEG2000 files.


You might want to check out <http://www.wilshipley.com/blog/2005/09/ jpeg2000-cool-but-slow.html> as well which includes the following quote:
Followup (9/19): The news gets even better, as it turns out 10.4's CGImageSourceCreateThumbnailAtIndex() is 3-7x faster at creating JPEG thumbnails than the method I had to use under 10.3: creating a CGImageRef using CGImageCreateWithJPEGDataProvider() and then drawing it (with antialiasing turned on) into a smaller window.






Glenn Andreas email@hidden
<http://www.gandreas.com/> wicked fun!
quadrium | flame : flame fractals & strange attractors : build, mutate, evolve, animate




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