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Eric SIBERT
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 Posted: Tue Jun 29, 2004 5:18 pm Post subject: streamed jpeg compression |
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Hi,
I'm handling large pictures (arround 16,000x16,000). I want to store it
in a jpeg file. To reduce memory use, I don't store the full picture in
memory using a TBitmap. I'm looking for a way to make the jpeg file
with only a small part of my large view rendered in memory, in order to
minimize memory use. Do you have any (free) idea?
Moreover, the underlaying organization of my large picture can be a full
resolution Y picture and the Cr and Cb pictures with half resolution. It
would be nice to use it for optimizing jpeg compression.
--
Eric SIBERT
http://www.ericsibert.com
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Joris Van Damme
Guest
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| Posted: Tue Jun 29, 2004 10:59 pm Post subject: Re: streamed jpeg compression |
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| Quote: | I'm handling large pictures (arround 16,000x16,000). I want to store it
in a jpeg file. To reduce memory use, I don't store the full picture in
memory using a TBitmap. I'm looking for a way to make the jpeg file
with only a small part of my large view rendered in memory, in order to
minimize memory use. Do you have any (free) idea?
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IJG's LibJpeg supports feeding the compressor scanline by scanline, and
retrieving scanline by scanline from the decompressor. As long as you don't
use stuff like interlacing, this should be ideal for your purposes (meaning
as low as possible buffering and memory consumption, and as high as possible
serial streamed processing).
Take a look at the docs accompanying LibJpeg (they should be distributed
with Delphi), and Borlands interface to it in TJpegImage, that should both
give you a pretty good idea. Furthermore, you should be able to use the
precompiled LibJpeg units distributed with Delphi for these purposes. As far
as 'free' is concerned, that's about the best you can get.
| Quote: | Moreover, the underlaying organization of my large picture can be a full
resolution Y picture and the Cr and Cb pictures with half resolution. It
would be nice to use it for optimizing jpeg compression.
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I know for sure you can feed LibJpeg compressor the YCbCr, but I don't
remember how exactly (it had to do with overriding the input and output
color space. Instead of first being RGB and second being YCbCr, you should
set them both to YCbCr). More information on this can surely be found in the
same LibJpeg docs. As to the feeding of downsampled Cr and Cb components,
I'm not sure. Quite possibly there's support for this, LibJpeg is quite
wonderfull and its author is very much concerned with good old optimal
behaviour. If not, don't hesitate to ask Tom Lane, I'm sure you'll get a
very good answer.
Joris Van Damme
[email]info (AT) awaresystems (DOT) be[/email]
http://www.awaresystems.be
Download your free TIFF tag viewer for windows here:
http://www.awaresystems.be/imaging/tiff/astifftagviewer.html
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Lord Crc
Guest
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| Posted: Wed Jun 30, 2004 2:11 am Post subject: Re: streamed jpeg compression |
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On Tue, 29 Jun 2004 19:18:35 +0200, Eric SIBERT
<courrier (AT) NOericSPAMsibert (DOT) com> wrote:
| Quote: | Moreover, the underlaying organization of my large picture can be a full
resolution Y picture and the Cr and Cb pictures with half resolution. It
would be nice to use it for optimizing jpeg compression.
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Regular JPEG can easily be downsampled 2:1 in the Cr/Cb channels, just
so you know  (it's usually done in the less than maximum quality
settings).
- Asbjørn
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Eric SIBERT
Guest
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| Posted: Wed Jun 30, 2004 4:39 pm Post subject: Re: streamed jpeg compression |
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| Quote: | IJG's LibJpeg supports feeding the compressor scanline by scanline, and
[...] |
| Quote: | Take a look at the docs accompanying LibJpeg (they should be distributed
with Delphi), and Borlands interface to it in TJpegImage,
[...] |
Many thanks. I found some parts. Not the documentation. I will look on
the net for it.
--
Eric SIBERT
http://www.ericsibert.com
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Eric SIBERT
Guest
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| Posted: Wed Jun 30, 2004 4:43 pm Post subject: Re: streamed jpeg compression |
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| Quote: | Regular JPEG can easily be downsampled 2:1 in the Cr/Cb channels, just
so you know
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Indeed, I want to do à 4:4:1. Because size of Cr/Cb channels is NxN when
Y is 2Nx2N.
--
Eric SIBERT
http://www.ericsibert.com
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Lord Crc
Guest
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| Posted: Wed Jun 30, 2004 8:07 pm Post subject: Re: streamed jpeg compression |
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On Wed, 30 Jun 2004 18:43:13 +0200, Eric SIBERT
<courrier (AT) NOericSPAMsibert (DOT) com> wrote:
| Quote: | Indeed, I want to do à 4:4:1. Because size of Cr/Cb channels is NxN when
Y is 2Nx2N.
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Ah, in that case i distinctly remember ijl takes a parameter for the
sampling frequency for each channel.
- Asbjørn
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