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[OM] Re: ( OM ) image sizes, dpi, pixels and pixes etc

Subject: [OM] Re: ( OM ) image sizes, dpi, pixels and pixes etc
From: Andrew Gullen <andrew.gullen@xxxxxxxxxxxx>
Date: Sun, 01 Aug 2004 22:15:00 -0400
on 2004/08/01 9:43 PM, Brian Swale at bj@xxxxxxxxxxxxxxx wrote:

> High Quality JPEG 3000x2000 pixels open file=17mb. Closed file=1.2mb
> Print up to 8x10
> 
> Please advise what format the open file is.  I doubt it is JPEG.
> Is it TIFF? or BMP? or what ??
> 
>> 
>> Yes, the files are JPEG. The JPEG file type compresses as it saves, and
>> decompresses as it opens - hence an 18 megabyte Tiff file, saved as a JPEG
>> will be around 3 megabytes as a saved JPEG. When the JPEG is opened again it
>> decompresses to the full 18megabytes of course (as the pixel count is still
>> the
>> same). If you use Photoshop, view the status bar at the bottom when you open
>> a
>> JPEG file, and compare it's open size to it's closed size.
> 
> Either we are speaking different flavours of English - or he doesn't know.

It's the former, I think.

I'm almost sure he's saying the file is a JPEG that is 1.2MB on disk, but
when it is opened the decompression expands it (as it's read into memory) to
17 or 18 MB of picture data. Thus the "open file" doesn't really have a type
- it's in whatever internal format the software that opened it uses (perhaps
just an array of pixel values).

Andrew


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