cctiff intent question

[Martin Lederhilger]

Hello,

I have a question regarding the intent switches of cctiff. I want to convert
with absolute rendering intent, and if I run cctiff with

cctiff -ip sRGB.icm -ia ISOcoated_v2_eci.icc rgb.tif cmyk.tif

then the output image is the same as if I converted with Imagemagick's
convert, or other tools I have tried. If I run cctiff with

cctiff -ia sRGB.icm -ia ISOcoated_v2_eci.icc rgb.tif cmyk.tif

then the output image is slightly different.

What is the reason why I can specify multiple intent options, and what does
the second cctiff invocation differently?

Thank you to give me some insight,

Martin

[Graeme Gill]

Post by Martin Lederhilger
I have a question regarding the intent switches of cctiff. I want to convert
with absolute rendering intent, and if I run cctiff with
cctiff -ip sRGB.icm -ia ISOcoated_v2_eci.icc rgb.tif cmyk.tif
then the output image is the same as if I converted with Imagemagick's
convert, or other tools I have tried. If I run cctiff with
cctiff -ia sRGB.icm -ia ISOcoated_v2_eci.icc rgb.tif cmyk.tif
then the output image is slightly different.
What is the reason why I can specify multiple intent options, and what does
the second cctiff invocation differently?

Hi,
each intent switch applies to the following profile. So in
the first case you are using the perceptual intent of sRGB.icm and the
absolute intent of ISOcoated_v2_eci.icc.

In the second case you are using absolute intent for both the profiles.

Naturally you end up with a different result, because you asked for
different things. Absolute intent gives you absolute colorimetry,
ie. instrument measurements. Since sRGB has a D65 white point, while
prints using ICC profiles are assumed to be viewed under D50, the
results will look somewhat blue.

Many CMM's, (including LittleCMS by default) follow the ICC's lead and
abuse Absolute intent when it comes to display profiles by disabling it.
To get the same results using ArgyllCMS as these crippled CMM's, simple
use relative colorimetric intent for the display profile.

Graeme Gill.

[Martin Lederhilger]

Post by Graeme Gill

Post by Martin Lederhilger
I have a question regarding the intent switches of cctiff. I want to
convert>
with absolute rendering intent, and if I run cctiff with
cctiff -ip sRGB.icm -ia ISOcoated_v2_eci.icc rgb.tif cmyk.tif
then the output image is the same as if I converted with Imagemagick's
convert, or other tools I have tried. If I run cctiff with
cctiff -ia sRGB.icm -ia ISOcoated_v2_eci.icc rgb.tif cmyk.tif
then the output image is slightly different.
What is the reason why I can specify multiple intent options, and what does
the second cctiff invocation differently?

Hi,
each intent switch applies to the following profile. So in
the first case you are using the perceptual intent of sRGB.icm and the
absolute intent of ISOcoated_v2_eci.icc.
In the second case you are using absolute intent for both the profiles.

Hi,

thank you for your answer.

Just to clarify that I have understood correctly: The first intent is for
converting from sRGB to PCS, and the second intent is for converting from PCS
to ISOcoated. Is that correct?

Thank you,

Martin

Post by Graeme Gill
Naturally you end up with a different result, because you asked for
different things. Absolute intent gives you absolute colorimetry,
ie. instrument measurements. Since sRGB has a D65 white point, while
prints using ICC profiles are assumed to be viewed under D50, the
results will look somewhat blue.
Many CMM's, (including LittleCMS by default) follow the ICC's lead and
abuse Absolute intent when it comes to display profiles by disabling it.
To get the same results using ArgyllCMS as these crippled CMM's, simple
use relative colorimetric intent for the display profile.
Graeme Gill.

[Graeme Gill]

Post by Martin Lederhilger
Just to clarify that I have understood correctly: The first intent is for
converting from sRGB to PCS, and the second intent is for converting from PCS
to ISOcoated. Is that correct?

Yes that is. It gives you the option of creating a "mixed intent"
transform such as Display relative colorimetric to Print absolute
colorimetric, while not disabling a true absolute colorimetric
transform.

Graeme Gill.