CHROMiX

reverse transformation from B2A0 to A2B0?

I want to know is it possible to create a reverse transformation from A2B0 if B2A0 is known . Also what is the use of keeping transformation of
other intent like A2B1 or A2B2 if the intent is perceptual for an ICC profile ?

At 5:18 AM -0800 11/28/05, pravin_med wrote:

I want to know is it possible to create a reverse transformation from A2B0 if B2A0 is known .

sort-of. It works better the other way around.

So, you are asking if you have, say, Lab->CMYK transform can you create CMYK->Lab? You could start with a bunch of in-gamut Lab values & calculate CMYK from them. Then use that CMYK and Lab data to build a profile in the normal manner. It would be a bit odd though.

As I mentioned, if you had the CMYK->Lab part of the transform then you could just start with some CMYK target data, convert to Lab and use the two to create a profile.

Also what is the use of keeping transformation of
other intent like A2B1 or A2B2 if the intent is perceptual for an ICC profile ?

Which intent would that be? The default intent? The intent setting in the header of a profile is the ‘default’ intent although it’s not typically called this. This means that if the user does not specify the intent, the CMM will use this default intent. There are very few places where the user is not required to specify an intent and that always overrides the default. So basically the A2B1 (rel col) and A2B2 (sat) intents will be used any time you select these intents in an application or RIP.

Regards,

Steve


o Steve Upton CHROMiX www.chromix.com
o (hueman) 866.CHROMiX


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Hi ,
If the Tx from CMYK to Lab is known then what I feel is the reverse Tx is not possible bcoz the Tx itself is not linear . And also if at all
the Tx is achived then that wont match the exact values of the reverse Tx. Is that true ?
Tx = Transformation.

At 10:19 PM -0800 11/29/05, pravin_med wrote:

Hi ,
If the Tx from CMYK to Lab is known then what I feel is the reverse Tx is not possible bcoz the Tx itself is not linear .

not possible? I don’t understand that…

And also if at all
the Tx is achived then that wont match the exact values of the reverse Tx. Is that true ?

generally, yes. Their purposes are different though. A2Bn is in the device gamut, by definition and is mostly about proofing. It can be used to recreate the measurement information if desired (loss of accuracy happens but if you have no choice…) B2A is in the PCS / Lab gamut so it has to accept all possible colors and deal with in-gamut and out-of-gamut intelligently…

Regards,

Steve


o Steve Upton CHROMiX www.chromix.com
o (hueman) 866.CHROMiX


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