Re: Converting to an input profile
Re: Converting to an input profile
- Subject: Re: Converting to an input profile
- From: Marco Ugolini <email@hidden>
- Date: Mon, 6 Aug 2007 17:12:22 -0700 (GMT-07:00)
In a message dated Aug 6, 2007 3:50 AM, Edmund Ronald wrote:
>Strange as it seems, I'm trying to get Photoshop to convert from a
>standard workspace to an existing camera profile, but it simply
>doesn't list these profiles as convert-to targets. Why ? Is this
>something that can be solved easily ?
Scanner profiles only work in one direction, from the input data (RGB) to the Profile Connection Space (PCS, which for scanner profile is usually XYZ). They use A2B (source-to-PCS) Look-Up Tables (LUTs) to translate device-dependent RGB data (the numbers created in the file by the scanning process) into unambiguous device-independent XYZ data.
In turn, those XYZ data in the PCS can be translated into a destination RGB color space via a direct profile-to-profile conversion: the XYZ values generated by the scanner profile for the data in a given scan are picked up by the B2A LUTs (PCS-to-destination) of the target profile (e.g., AdobeRGB), and translated into the RGB numbers that provide, within the destination's color space, an appearance as close as possible to that described in the source.
Clearly, PCS-to-Destination conversion is not what scanner profiles are meant to do: they are only meant to assign an unambiguous color appearance to the input/source data acquired via the scanner whose behavior they describe. They have no other legitimate functions: they are not meant to receive data from other files and output them into their own color space. They are *always the first step* in a chain of data, never an intermediate step between another file and an output.
That's why they don't have any B2A tables within them -- a fact that you can verify by double-clicking any scanner profile in Mac OS X and looking at its tags: you will find A2B tags, but no B2A tags.
Marco Ugolini
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