#### Lorna Wiles

##### Member

eg: The A2B tables in printer profile would be used soft proofing but why not just use the inverse of the B2A tables to map the printer gamut back to the PCS.

The relevance of this can be seen within a work flow where an input profile equals the output profile. I have been using this work flow (I now realise incorrectly!) within a RIP to effectively turn off the colour management assuming that if the input gamut was the same as the output gamut no mapping would take place.

Oddly this 'assumed' behaviour can be confirmed in Photoshop under Edit > Convert to Profile. If the selected 'Destination Space' is the same as the 'Source Space' then no transformation takes place and different rendering intents have no effect on the output.

However this is not what happens within my (old!) workflow in the RIP where a transformation dose takes place. Here, the numbers in do not equal the numbers out. This would seem to confirm that the B2A tables and the A2B are different and that gamut mapping is different in each direction.

Can anyone help with my understanding please?

1) Why there is a difference when converting in Photoshop and when converting in the RIP as explained above?

2) Why dose an output profile requires the A2B tables instead of just using the inverse of the B2A tables (and presumably vice versa for an input profile)?

Many thanks