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Author Topic: X-Rite Passport - What's the RGB value of the white balance page?  (Read 4426 times)
Dinarius
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« on: September 18, 2010, 07:44:06 AM »
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I'd like to know the RGB value (in Adobe 1998) of the white balance page of the X-Rite Passport.

Alternatively, the LAB value would do.

Any ideas?

Thanks.

D.
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bjanes
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« Reply #1 on: September 18, 2010, 09:43:13 AM »
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I'd like to know the RGB value (in Adobe 1998) of the white balance page of the X-Rite Passport.

Alternatively, the LAB value would do.
According to the X-rite web site, the White Balance card is a full size reproduction of the white reference square of the 24 patch ColorChecker (patch A4 in the customary nomenclature). The values you are seeking can be determined from Bruce Lindbloom's Color Checker Calculator:



Please note that the *a and *b values are not equal, and the patch is not truly neutral. This has been discussed in a thread on Photo.net:
http://photo.net/digital-darkroom-forum/00I6Ak?start=10

Patch B4 is usually recommended for color balance and it is more neutral as discussed in the thread. This is a bit confusing, and comments by color management gurus on the forum are welcome.
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crames
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« Reply #2 on: September 18, 2010, 10:28:41 AM »
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According to Robin Myers technical report on the Passport, http://www.rmimaging.com/information/ColorChecker_Passport_Technical_Report.pdf, the white balance page is similar to, but more neutral than the N8 (second white patch) on the standard ColorChecker.

The actual spectral measurement of the white balance page is also available at Robin Myers' site, along with SpectaShop, which in demo mode will translate the spectral info to CIELAB and RGB values. Spectrashop shows shows AdobeRGB values = R 201, G 201, B 200, and CIELAB  = L* 81.34, a* -0.22 b* 0.36.

Rgds,
Cliff
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Cliff
bjanes
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« Reply #3 on: September 18, 2010, 11:31:30 AM »
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Cliff,

That is useful information. The X-rite information that I quoted must be wrong. They should get their act together. A disadvantage of the White Balance card reported in the review is that the target is cardboard with paint. One use in the rain may ruin it. In contrast, WhiBal target is solid plastic and is nearly indestructible with normal use.

Bill
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crames
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« Reply #4 on: September 18, 2010, 01:17:58 PM »
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That is useful information. The X-rite information that I quoted must be wrong. They should get their act together. A disadvantage of the White Balance card reported in the review is that the target is cardboard with paint. One use in the rain may ruin it. In contrast, WhiBal target is solid plastic and is nearly indestructible with normal use.

Hi Bill,

The information is not easy to find. You would think that X-rite would have it easily accessible (maybe I overlooked it), but I had to go to the other source. The patches on the 24-patch card are also paint, so there is always the risk of damage. I have an original, full size ColorChecker that's about 16 years old, and it has held up very well (never rained-on, and checked periodically with a spectro).

Cliff
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Cliff
BartvanderWolf
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« Reply #5 on: September 18, 2010, 07:14:14 PM »
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In contrast, WhiBal target is solid plastic and is nearly indestructible with normal use.

Hi Bill,

Indeed. Here is the spectral evaluation of one of my copies (comparison between the WhiBal and the BabelColor White Target):


Cheers,
Bart
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crames
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« Reply #6 on: September 18, 2010, 07:47:00 PM »
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Hi Bart,

Just curious, what are the a* and b* of your Whibal?

Cliff
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Cliff
BartvanderWolf
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« Reply #7 on: September 18, 2010, 08:41:00 PM »
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Just curious, what are the a* and b* of your Whibal?

Hi Cliff,

I don't have that info anymore, I'll have to re-evaluate (cleaning before measuring makes a difference Wink ). FWIW the BabelColor target had a Lab reading of L=0.97, a=-0.2, b=-0.4 (according to Gretag MacBeth EyeOne Share).

Cheers,
Bart
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crames
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« Reply #8 on: September 18, 2010, 09:31:40 PM »
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The X-Rite White Balance seems to be a little flatter (or more neutral) than the Whibal:

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Cliff
Dinarius
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« Reply #9 on: September 19, 2010, 03:18:36 AM »
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Thanks for the feedback. A cursory glance at the white balance target will tell you that it is NOT the same as the white patch on the colour checker. This is what makes me despair of X-Rite.  Huh

I have been using a basICColor grey card for white balance and, in typical German fashion, the exact technical spec is readily available - Lab is 60, 0, 0 which equates to RGB of 143 in Adobe 1998.

The X-Rite target should have a known value and simply saying that it 'more neutral' isn't just sloppy, it renders it unusable. Wouldn't you say? Surely it needs to be neutral - period!

Thanks again.

D.
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BartvanderWolf
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« Reply #10 on: September 19, 2010, 04:43:56 AM »
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I have been using a basICColor grey card for white balance and, in typical German fashion, the exact technical spec is readily available - Lab is 60, 0, 0 which equates to RGB of 143 in Adobe 1998.

I don't know what (spectral data) info comes with the basICColor greycard, but according to the PDF on their website the a* and b* values are not zero (which would be unlikely anyway, there is bound to be some variation). They mention that under the D50 illuminant a=-0.18 and b=-0.41. Besides, these values vary with different illuminants, and a single coordinate doesn't tell the whole story.

@Cliff, I've just remeasured one of my WhiBals, it's L=72.0, a=-0.1, and b=0.8 (+/- 0.1 across the surface, under a D50 illumination, 2 degree observer regime).

Cheers,
Bart
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Dinarius
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« Reply #11 on: September 19, 2010, 07:23:57 AM »
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Bart,

Can you please provide a link to the PDF on the basICColor website?

Many thanks.

D.
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crames
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« Reply #12 on: September 19, 2010, 07:33:42 AM »
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I don't know what (spectral data) info comes with the basICColor greycard, but according to the PDF on their website the a* and b* values are not zero (which would be unlikely anyway, there is bound to be some variation). They mention that under the D50 illuminant a=-0.18 and b=-0.41. Besides, these values vary with different illuminants, and a single coordinate doesn't tell the whole story.

@Cliff, I've just remeasured one of my WhiBals, it's L=72.0, a=-0.1, and b=0.8 (+/- 0.1 across the surface, under a D50 illumination, 2 degree observer regime).

Thanks. Here is a summary for future reference:

D50 Lab
-----------L*--------a*--------b*-------C*
Basiccolor          -0.18     -0.41     0.45
Whibal     72.0     -0.10     -0.80     0.81
X-Rite     81.3     -0.18      0.28     0.31


The C* column is CIELAB Chroma, a combined measure of a* and b*.

@Dinarius - according to the Robin Myers report I linked to previously, the target values for the X-Rite in ProPhotoRGB are (190, 190, 190), and eciRGBv2 are (205, 205, 205). Since all RGB numbers are equal in these D50 spaces, maybe one of these spaces will be more convenient for doing a one-click balance.
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Cliff
BartvanderWolf
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« Reply #13 on: September 19, 2010, 07:39:01 AM »
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Can you please provide a link to the PDF on the basICColor website?

Hi D.,

I can only find it on the German language page: http://www.basiccolor.de/cms/de/03produkte/produkte/greycard.html

There you can find a link to the product brochure: http://www.basiccolor.de/cms/PDF/brochures/de/Graukarte.pdf
It's in German, but on page 6 you'll find a list of (I assume, aim) values under diffferent lightsources. Of course the product they compare with is pretty poor, a transparent sales trick.

Cheers,
Bart
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bjanes
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« Reply #14 on: September 19, 2010, 08:49:08 AM »
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The information is not easy to find. You would think that X-rite would have it easily accessible (maybe I overlooked it), but I had to go to the other source. The patches on the 24-patch card are also paint, so there is always the risk of damage. I have an original, full size ColorChecker that's about 16 years old, and it has held up very well (never rained-on, and checked periodically with a spectro).
Clif,

It is interesting to learn that your 18 year old color checker is still going strong. I've heard that x-rite says the lifespan of the ColorChecker is limited, and this review states that the claimed lifespan is two years. My own copy is quite a bit older than two years and it seems to be going strong, but I don't have a spectrophotometer to check it. With a two year life-span, x-rite would sell a lot more of them.

Bill
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crames
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« Reply #15 on: September 19, 2010, 09:52:28 AM »
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It is interesting to learn that your 18 year old color checker is still going strong. I've heard that x-rite says the lifespan of the ColorChecker is limited, and this review states that the claimed lifespan is two years. My own copy is quite a bit older than two years and it seems to be going strong, but I don't have a spectrophotometer to check it. With a two year life-span, x-rite would sell a lot more of them.

Bill,

It's never been left exposed to light very long - it's always in the cardboard slipcase except for the few minutes it takes to shoot it. That doesn't happen more than a couple times a year. A few years ago I submitted the spectro data to Danny Pascal to be included in his study of the ColorChecker http://www.babelcolor.com/main_level/ColorChecker.htm, and he provided a comparison of mine to his average at the time.

I guess you can keep using it forever as long as it's remeasured periodically.
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Cliff
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