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[OM] Re: scratch line on digital image

Subject: [OM] Re: scratch line on digital image
From: Philip Pemberton <oly@xxxxxxxxxxxxx>
Date: Wed, 13 Dec 2006 15:58:24 +0000
John Hudson wrote:
> You mention "JPEG blocking". What is this, what causes it and where is it
> seen on the image?

JPEG blocking, also known as JPEG Compression Artefacting is an effect you get 
from the JPEG compression algorithm.

Basically, JPEG chops an image into 8x8 pixel blocks (or 16x16 if you have the 
compression turned WAY up), then processes those blocks, repeating previous 
blocks as necessary to save space. At some compression levels, those 8x8 
blocks are visible - that's JPEG blocking.

... Which is why you save the RAWs, convert to JPEG for display, and print 
from uncompressed TIFFs. Or at least that's what I do. Maybe I'm just a little 
obsessive about quality :)

-- 
Phil.                         |  (\_/)  This is Bunny. Copy and paste Bunny
oly@xxxxxxxxxxxxx             | (='.'=) into your signature to help him gain
http://www.philpem.me.uk/     | (")_(") world domination.

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