Re: Fast Thumbnails - or why multimedia is not possible with Java

[Dieter Krachtus <di...@googlemail.com>]

Hi Charles,

Sanselan is a great project. I want to draw your attention to the fast
thumbnail-feature for jpegs not available in java. I attached a mail where I
describe the problem to somebody else.

Do you think you could implement this feature as part of Sanselan? Perhaps
one could do it in such a way (e.g. special InputStream) so it could also be
used together with ImageIO/JAI etc.

What do you think?

Cheers,
Dieter



2008/7/26 Dieter Krachtus <di...@googlemail.com>

> Hi Kenneth,
>
> The Problem with Java ImageIO:
> Why is Java bad for multimedia - because we have no thumbnail-method
> that is fast.
>
> Analysis of the problem:
> - Java uses native ijg library (http://www.ijg.org) to load images.
> - Programs like ACDSee and Picasa also uses ijg to load images and
> thumbnails.
> - So why are they faster by a factor 10-100 and and need far less memory?
> - Answer: Java's ImageIO is not using the most valuable feature of ijg!
>
> Java uses JNI to take advantage of the ijg library.
> This means Jpeg decoding (and also encoding is very fast). Still, if you
> want to create thumbnails of hundreds of jpegs it still takes ages if you
> need to decode the full picture and then scale it to thumbnail size. To
> overcome this obstacle ijg allows you to get a picture 1/2,
> 1/4, 1/8 or even 1/16 in size of the original picture. E.g. for a factor
> 1/8, a 5000x5000 picture will be returned as 625x625 picture.
>
> Although Java uses ijg one cannot tell ijg to just load 1/8 of the image.
> One always has to read and decompress all of the 5000x5000 pixels and then
> draw it in a much smaller thumbnail. This is very slow and needs very much
> memory!
>
> How does this feature allow fast thumbnails?
> How does this feature of ijg work? If Java would tell the ijg library to
> get a picture 1/8 in size of the original picture, the ijg library only uses
> the DC components and skips all the AC components. This means it only has to
> decrypt the DC component. It still has to do the full Huffman decompression,
> but still it saves a hell lot of time, especially since it has to read much
> less data from the disk.
>
>
> How to fix this problem?
> It took me a lot of time to track down this problem and get up-to-date with
> the theory. Still I have little experience with the JNI-ijg bridge used in
> ImageIO. I think the best way to do it is to extend the JNI interface and
> allow the user to set 1/2, 1/4, .., in JPEGImageReadParam and communicate it
> to ijg.
>
>
> In my opinion this single feature would have more impact on Java's
> multimedia capability then any other optimization I can think of. Video
> being the exception.
>
>
>
> Cheers,
> Dieter
>