Re: Image compression
On Wed, 21 May 2008 22:50:56 -0500, Mumia W.. wrote:
> On 05/21/2008 03:02 PM, Hendrik Boom wrote:
>> I've noticed that some 40K byte jpeg files are very good, as good as
>> ones ten times the size, and that others are awful. The question
>> naturally arises about the proper way to further compress the large
>> images to save disk space.
>>
>> What image compression programs have people found to give good results?
>>
>> And to what extent is good image quality the result of the algorithms
>> that display the image, adjusting image size to screen size and
>> resolution and the like?
>>
>> -- hendrik
>>
>>
>>
> First, you can't recompress JPEGs without degrading them permanently, so
> don't do that unless you don't care about the data.
I'm aware of this. It's a damage/disk-space/processing-time tradeoff.
> Second, I've heard that progressive JPEG compression can outperform
> "normal" JPEG compression, so you're probably witnessing the advantage
> of progressive JPEGs. The program cjpeg (part of libjpeg-progs in
> Debian) can create progressive JPEGs.
Thanks. I'll try it out sometime.
I google for "progressive jpeg" and find http://www.faqs.org/faqs/jpeg-
faq/part2/section-15.html, which tells me that there's also jpegtrans,
which losslessly converts between baseline and progressive JPEGs. So if
progressive really outperforms baseline, It may have to do with the
orograms that implement it rather than any inherent capability of the two
file formats. Unless there's a lot of useless overhead in the baseline
format, but I can't see compression experts designing useless overhead.
>
> HTH
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