Mike Chaney's Tech Corner

This is about white balance, the X-rite colour checker and the Passport version for making camera profiles.
I thought some of you may be interested.  :-\
For some time I've had a Mini colour checker (see attachment 1) which I bought as a convenient and accurate way to calibrate white balance on images. I use it on most of my photo sessions. It's only 80 x 60mm (3.25 x 2.25ins) and I keep it in a credit card wallet. Over time I've noticed there's some variation on the grey patches, probably due to it getting a bit grubby.
I should say those cheap plastic credit card size grey cards are useless, I've tried several!

I've now bought an X-rite Color Checker Passport (see attachment 2). It is 125 x 90mm (5 x 3.5in) so still quite compact. It has 3 "pages" in a robust plastic booklet: 24 colour patches, a white balance patch and a page with special effect WB patches. I'm not yet sure how that one is used! I've now been able to check my  mini color checker and confirmed some grey patches are no longer a true grey but there are some that are useable, which is good because it's a more convenient size to use when out and about.

One feature of the Passport is that the 24 patches can be used to create a camera profile "for a single lighting condition" and software is supplied to do this. (attachment 3)
However X-rite succumbed to Adobe and it needs a dng raw file and makes a dng profile instead of an international-standard icc profile. All is not lost because other software users (Capture One in particular) have complained and a beta version of the software is now available that makes ICC profiles too. This requires the raw to be converted to a tiff without any profile embedded.
In QU, I found the best way to do this is with Print to File. To turn off embedding a profile, click to "Select a Different ICC Profile" and in the next window un-tick "Enable". I could not see a way to do this using the Convert feature.

I did make a profile but not in ideal conditions, it was cloudy and I had a significant WB correction on the raw file.
Needless to say the profile was not as good as the QU supplied one for my 80D. Using only 24 patches instead of an IT8 target is bound to have an effect. It may be of use in an emergency but at least I now have a reliable white balance standard.
Terry

Terry,
Excellent dissertation.
I was wondering ... a thought. Would it be worth the effort to compare the camera profile you make with setting Adobe rgb icc as the camera profile just to evaluate?
Fred

Very interesting read.

79 quid made me cough  :)

My colormunki came with a 80 x 60 card, I wasn't able to make head nor tails of it, so left well alone and camera on auto.

Go on, have another 'go' at me.

jeff

I'm not how that would work but ...
I re-made that X-rite profile in full sun with the target in my car boot (=trunk) to exclude extraneous light. Some gamut comparison programs and web sites will not read it. One program that does work seems to indicate it's gamut is smaller that the QU profile, reds particularly.
Jeff,
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I will! I have found that auto WB on my Canon cameras don't do a particularly good job. It can often make a big difference to the colour of an image. Do you ever check an image WB out in raw refine by using a know grey area in the image? That at least would be a good idea. I do that sometimes as the grey card shot(s) are not always truly representative.
You can't take it with you.
Terry

I haven't found any ICC profile inspecting programs that will read a V4 ICC profile.  Maybe when I retire, I'll write one.  ;)

I would never trust an ICC profile made from a 24 patch target.  They just don't cover enough of the gamut to be useful in creating a profile.  I could see it being helpful if you have serious color casts that you want to remove, but beyond that, you can't count on them to be "accurate".  I started using the x-Rite Digital Color Checker SG a few years ago for creating camera profiles.  You may not want to look that one up if you value your "quid".  It'll make you go quid pro OH NO.  :D

Mike

.
I will! Do you ever check an image WB out in raw refine by using a know grey area in the image? That at least would be a good idea. I do that sometimes as the grey card shot(s) are not always truly representative.

You can't take it with you.
Terry

That is exactly how I treat the white balance problem, if I think image is off colour balance, ctrl key and select a grey area, if I don't like that result resort to manual, mark one eye ball.

There will be almost nothing left to take with me.  Just enough to engrave stone "I told you I was poorly.  Grumpy"

Jeff

 

[/quote]

Mike, thanks for your response
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No need, there is one that works Gamutvision http://www.gamutvision.com/ (http://www.gamutvision.com/)
I must say I had my doubts when a 24 colour patch is used for a camera profile. I think X-rite are claiming too much even when saying it's "for a single lighting condition". Anyway it's not necessary for to cret camera profiles any more with everything covered in QU.
I'm curious, so does that mean you got hold of all those  cameras to create the image for profiling or is there another source?
Jeff,
Looking at your photos online I can see that WB is not just by camera auto. Yes that CTRL key feature is very useful too  ;)
Terry

A few are from my own cameras and the rest of the story is a trade secret.  I can only say that it helps to have contacts at local camera shops and live in a sunny place.  There are some reports of people seeing a guy parked facing north in a parking lot with his trunk lid up taking pictures of something in his trunk.  Just ignore those.  ;)

There are also rumors about some rogue version of Profile Prism that can read color patches from that Digital Colorchecker SG chart.  Best to ignore those too.

Mike

I like that  ;D
Some of my neighbours  commented about a me the other day taking photos of the inside of my Boot (=trunk)  ::)
Terry