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Re: [OM] JPEG quality loss - some data

Subject: Re: [OM] JPEG quality loss - some data
From: Frank van Lindert <Frank@xxxxxxxxxxxxx>
Date: Mon, 09 Mar 2009 11:21:10 +0100
Doug, 

Thanks for all the efforts and for answering my questions.

But I remain firm on the issue that successive saving as jpeg serves
no purpose at all.

When you work on a photo, and expect having to work extra on it in a
later stage, you should never save as jpeg. That is not what
compressing is for: you will always loose quality (as you demonstrated
clearly).

It is like making an old film negative, print it, and for further
editing use the print rather than the negative, make a new negative of
that print and so on... nobody would do that unless the negative was
no longer available

IMHO one should always  
1. save the orginal raw file (like the negative)
2. save the intermediate results in any no-loss format, e.g. tiff
3. compress to jpeg only after finishing all editing jobs

In Oly Studio 2 I use Exif-TIFF . (btw: tiff can be compressed too,
but remains lossless).

Frank van Lindert
Utrecht NL.


On Mon, 9 Mar 2009 04:24:49 -0400, Doug wrote:

>Chuck posted a note copied from the PWP forum and it got my curiosity up about 
>the subject.
>I did some experimenting and posted some of it to the web space that comes 
>with my ISP. 
>
>http://members.localnet.com/~doug9345/JPEG_Compare.html
>
>I left the pictures fairly large and generally not highly compressed. I didn't 
>want to and any other sources of changes than the ones I was experimenting 
>with. It loads fairly slow on dial-up. If it gives enough people loading 
>issues I'll reduce the size of the pictures. It will take me about 3 more 
>passes to get rid of the typos, spelling and grammer mistakes.
>
>To answer your question repeated saving isn't to reduce file size but a by 
>product of working on a photo, saving it, and then coming back, working on it 
>some more and saving it again.
>
>How the file size varied from one save to the next depended on the quality of 
>the save. For my image of corn at 1000 x 800 pixels the tif is 6.7MB,and the 
>png with maximum compresion 2.3 MB.  the best quality jpeg is 694.7KB. After 
>9 more saves it is 622.4KB. On the other had with the quality set to 50 on a 
>scale of 100, the first save after the highest quality one is 78.2KB. It the 
>climbs to 78.5 on the final save. Using bzip2 to compress the tiff gave me a 
>file size of 1.6MB. The png, compressed the same way, was 1.5MB. The high 
>quality jpeg increased in size 694.7KB to 695.8KB when compressed. This is 
>normal behavior for already compressed files. I hope this answers your 
>question.
>
>-Doug
-- 
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