[argyllcms] Re: ArgyllCMS: shadow details and blue color issues. What I'm doing incorrectly?

  • From: "Xavi" <aruiz@xxxxxxxxxxx>
  • To: <argyllcms@xxxxxxxxxxxxx>
  • Date: Thu, 25 Oct 2012 00:30:34 +0200

Hi Graeme!

"You can also then check the profiles self consistency. How much different
is the relative colorimetric B2A for a given neutral color compared to
xicclu -fif ? "

.\xicclu -fif -s255 -ia
MP_B01_A4_HPEverydayBrilloIIQ1Dif_NoVPre_396p64g3bArgyllv140_121011Opcio_qm_
ACPU.icm
50
50.000000 0.000000 0.000000 [Lab] -> Lut -> 145.854104 129.484272 161.454493
[RGB]

.\icclu -fb -ip -s255
MP_B01_A4_HPEverydayBrilloIIQ1Dif_NoVPre_396p64g3bArgyllv140_121011Opcio_qm_
ACPU.icm
50
50.000000 0.000000 0.000000 [Lab] -> Lut -> 143.773602 127.621559 160.768615
[RGB]

.\icclu -ff -ia -s255
MP_B01_A4_HPEverydayBrilloIIQ1Dif_NoVPre_396p64g3bArgyllv140_121011Opcio_qm_
ACPU.icm
146 129 161
146.000000 129.000000 161.000000 [RGB] -> Lut -> 49.919833 0.200034 0.187522
[Lab]

.\icclu -ff -ia -s255
MP_B01_A4_HPEverydayBrilloIIQ1Dif_NoVPre_396p64g3bArgyllv140_121011Opcio_qm_
ACPU.icm
144 127 161
144.000000 127.000000 161.000000 [RGB] -> Lut -> 49.203759 0.331625
-0.807751 [Lab]

It's my converssion correct? If it indicates that I must to read with my
spectro a 49.919833 0.200034 0.187522 [Lab] or a 49.203759 0.331625
-0.807751 [Lab] on my prints when I print a 50,0,0 Lab, I must to say that
in any case my spectro read these values. The more aproximate values that I
have read are: 53,57    -0,13   1,06 [Lab] and 52,86    0,81    2,15 [Lab]
both with exactly a DeltaE00 of 3,68.

"It's not that reasonable to be looking at delta E's of non-neutral colors
for perceptual rendering, unless you really understand what's going on.
By definition it is not colorimetrically accurate - it aims at a pleasing
reproduction that tries to preserve the look of the original (ie. not
clipping) while staying within gamut."

Yes I know. But I think that the perceptual rendering intent can alterate
the inside gamut colors, with some limit. For example, the yellow and the
blue color, in my case,are evidently different from the source using
perceptual intent. Using the same profile but with the relative colorimetric
rendering intent, the results are more similar to source.


Tahnk you for your help me to find what is incorrect in my case.

Best Regards, 
Xavi.


-----Mensaje original-----
De: argyllcms-bounce@xxxxxxxxxxxxx [mailto:argyllcms-bounce@xxxxxxxxxxxxx]
En nombre de Graeme Gill
Enviado el: lunes, 22 de octubre de 2012 9:33
Para: argyllcms@xxxxxxxxxxxxx
Asunto: [argyllcms] Re: ArgyllCMS: shadow details and blue color issues.
What I'm doing incorrectly?

Xavi wrote:
> Dear Graeme.
> 
> I enjoy reading your replies although I discover that my knowledge of 
> color management is very basic.
> 
> All the images that I use to test the printer profiles, are mainly 
> labelled with the AdobeRGB and the others with the sRGB color spaces. 
> Then, seems that this is not the reason of color change.
> 
> As I commented to you,  I have changed all the cartridges of my 
> Pro9000 to use another brand of ink, to have more chances to discover 
> what is happening. Then I can't use at this moment, the printer with 
> the ink of the example of ICM that you used in your icclu example 
> (Argyllv140_396parxes48Gris3Blanc.icm).
> 
> I must to use the MP540 printer with the 
> "MP_B01_A4_HPEverydayBrilloIIQ1Dif_NoVPre_396p64g3bArgyllv140_121011Op
> cio_qm _ACPU.icm". Sorry to the extent name, but I have created a lot 
> of profiles and the name was growing trying to identify them.
> 
> I have do the same example, than you show me, using this ICM:
> 
> .\icclu -fb -ip
> MP_B01_A4_HPEverydayBrilloIIQ1Dif_NoVPre_396p64g3bArgyllv140_121011Opc
> io_qm_
> ACPU.icm
> 50
> 50.000000 0.000000 0.000000 [Lab] -> Lut -> 0.563818 0.500477 0.630465 
> [RGB]
> 
> .\icclu -ff -ir
> MP_B01_A4_HPEverydayBrilloIIQ1Dif_NoVPre_396p64g3bArgyllv140_121011Opc
> io_qm_
> ACPU.icm
> 0.563818 0.500477 0.630465
> 0.563818 0.500477 0.630465 [RGB] -> Lut -> 52.109114 0.326121 
> -0.977612 [Lab]

Hi,

> I don't know if the reading with an spectro some patches, is a good 
> way to show you what I obtain on prints but I have print a simulation 
> of the patches of a colorchecker card and I have read the results with a
spectro.

Without knowing the workflow of how those colorchecker values made their way
to the print (ie., measured colorchecker values reproduced using absolute
colorimetric reproduction ?), I'm not sure this leads anywhere.

It's far better to directly check critical spot colors against the profile.
For instance, pick a neutral color (say Lab 50,0,0), then look it up using
the absolute colorimetric B2A table, then print that RGB value using the
same print path as the test chart. Measure it. Check the delta E against the
target.
etc.

You can also then check the profiles self consistency. How much different is
the relative colorimetric B2A for a given neutral color compared to xicclu
-fif ?

[Note - an instrument measurement by default will correspond  to absolute
colorimetric rendering intent. ]

If the colorimetric model of the profile matches the device reasonably well,
then you can look into the behaviour of the perceptual rendering (as I was
doing using the icclu).

> Applyiing the icclu example that you show me to the values of blue 
> color
> patch:
> 
> .\icclu -fb -ip
> MP_B01_A4_HPEverydayBrilloIIQ1Dif_NoVPre_396p64g3bArgyllv140_121011Opc
> io_qm_
> ACPU.icm
> 28.87   14.81   -50.15
> 28.870000 14.810000 -50.150000 [Lab] -> Lut -> 0.358232 0.399245 
> 0.879326 [RGB]
> 
> .\icclu -ff -ir
> MP_B01_A4_HPEverydayBrilloIIQ1Dif_NoVPre_396p64g3bArgyllv140_121011Opc
> io_qm_
> ACPU.icm
> 0.358232 0.399245 0.879326
> 0.358232 0.399245 0.879326 [RGB] -> Lut -> 39.085966 11.557139 
> -49.964686 [Lab]
> 
> I must obtain, on paper and with perceptual intent, a patch with 39.09
11.56
> -49.96 Lab values, but I read a patch with 39,35      4,45    -48,45 Lab
> values. That's a deltaE76 of 11,77.

It's not that reasonable to be looking at delta E's of non-neutral colors
for perceptual rendering, unless you really understand what's going on.
By definition it is not colorimetrically accurate - it aims at a pleasing
reproduction that tries to preserve the look of the original (ie. not
clipping) while staying within gamut.

Graeme Gill.



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