Hi Daniel, In my inexperience I did not realize the task of matching color up under CFL and daylight different light sources would be so difficult. A couple helpful and knowledgeable people like yourself have indicated to me this is beyond the capability of a simple color checker card (and as you say, may be impossible). I understand what you're saying about wavelengths and that's a great point. I realize now, like you and others have said, I would be better off changing the light. There is the other issue which has received little attention, and that is the lack of improvement using the Colorchecker Passport and profile software in daylight conditions. My understanding at this point is that daylight is a continuous spectrum light and should be easier to color correct for with such tools (along with incandescent). However, the Adobe Standard profile does as good of a job, if not better than the Passport in my test. Colors come out punchier with the Passport, but not more accurate in general (using the 4 swatches I tested, the exception being the yellow swatch which was barely more accurate). Also it did not match colors between cameras. I would not call the X-rite Passport a useful tool for precisely these reasons. I've spent a lot of time trying to understand why it hasn't worked as well as advertised and finally got around to doing some objective testing. Ultimately it's provided very little value. I've also tested it using the Adobe DNG profile, which does not do much better. So I think I understand better the vagaries of getting color right under spiky vs. continuous light sources. But I'm still interested in getting feedback on the performance of the Passport under the conditions I mentioned, and if generating an ICC profile is something people would recommend I do for architectural photography. Thanks very much. -Justin
Date: Sun, 22 Sep 2013 01:25:26 -0700 Subject: Re: X-Rite Passport Inaccuracies From: daniel@westcott.us To: colorsync-users@lists.apple.com
Hi justin.
I once lectured on invention at a museum to several groups of school children at various grade levels. I asked the color of an object. Hands shot up. "Red!" I turned out the lights and asked again. The older groups still thought it was red but the youngest groups had the correct answer, black. You can only capture the color that exists when you take your exposure. There are wavelengths in daylight, warm or otherwise, which simply do not exist in CWF and you will never be able to capture something which does not exist. Trying to make a daylight exposure colorimetrically match an exposure taken in a lesser light source may or may not even be possible depending on what color is coming back from the object of the exposure.
My point is that if you wish to have a match, fix your light pre-capture. Your results will be far superior to trying to extrapolate from a few color chips what the exposure would have liked like had the color you wish you had actually been in the room when you made the exposure.
Remember that light is analog and that compression and decompression of an analog signal comes at a cost. Once something is gone you cannot regain it by decompressing. .. would you expect different results if the signal were never there to begin with as is often the case when shooting in light with deficiencies in certain wavelengths (e.g. CWF)?
For what it's worth, $100 is not very much to spend for a useful tool, but you need different and much more costly solutions to accomplish your goals.
Cheers Daniel Westcott
Perfect logic is meaningless without perfect perspective.
Daniel Westcott daniel@westcott.us
-------- Original message -------- From: Spinnaker Photo Imaging Center <spinnakerphotoimagingcenter@dnmillerphoto.com> Date: 09/20/2013 12:16 PM (GMT-07:00) To: Justin Krug <jkrug@hotmail.com> Cc: colorsync-users@lists.apple.com Subject: Re: X-Rite Passport Inaccuracies
On Sep 20, 2013, at 12:13 PM, regarding
my issues with the X-rite Passport. My primary purpose for using it is to get accurate and consistent colors across different ambient and artificial light sources for architectural photography. For example, I want the colors in the photo taken with ambient/artificial mixed light to match with those taken under CFL's at night.
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