Doug Kerr
Well-known member
The X-Rite Passport is a foldable set of color targets, now supported by new software packages. I thought I would take a quick look to see just what is going on here.
In my after (Sunday) breakfast theory lecture today, I conjectured that this set of tools might give us the opportunity to do color balance that takes into account the fact that some light sources do not have power spectral density functions (SPD) such that white-balance color correction based on a simple determination of the chromaticity of the illumination will approach "theoretical ideal" white balance color correction.
My conclusion is that it does, even though the single presentation of its use by the manufacturer I have so far looked at (the "Photoshop" version of their video) only hints at it.
The device (I describe it as "Barbie's eye shadow compact") includes three targets:
• A neutral gray target for making traditional white-balance color correction measurements.
• A "GretagMacbeth Colorchecker Classic" target, a pattern of numerous small patches of known reflective spectrum. My discussion here will concentrate on this.
• A target including various patches of nearly-neutral reflective color but not quite. Its purpose is to be used in post-processing to provide color correction that intentionally varies slightly from "theoretically-ideal" so as to "beautify" the subject's skin. (We have encountered this notion before in connection with one of Drew Strickland's products.)
The associated software allows us to use a shot of the second of these targets to build a camera profile (spoken of as a "DNG" color profile, although that may not be a meaningful description).
This profile describes the color response (in both luminance and chromaticity, I assume) at various places in the color space (that is, for the object colors of the patches), taking into account the illumination on the target.
Now, if we invoke this profile when processing a camera raw file, it will overcome inconsistencies in the camera's response across the color space, taking account of the illumination while it's at it, assuming that the illumination for the actual shot is the same as that used to shoot the target. (This is the same kind of thing we do with respect to the response of a printer when we construct a profile for it.)
The video mentions that of course, ideally this should be done separately for "various kinds of illumination" (tungsten, daylight, etc.), and the appropriate profile used when processing raw files for shots taken under that "type" of illumination.
But it would in fact seem advantageous, when dealing with "difficult" lighting situations (as those Asher so poignantly described for us in connection with his work at Colburn) to make such profiles on an "ad hoc" basis (for example, for shots to be taken on a certain region of the stage with a certain lighting setup in effect).
This does not require anything complicated in production - just shooting the ColorChecker target at a key spot on the stage for each scenario. The heavy lifting is done by the new X-Rite software during post.
Well, that's how it looks after about ten minutes' contemplation.
Best regards,
Doug
In my after (Sunday) breakfast theory lecture today, I conjectured that this set of tools might give us the opportunity to do color balance that takes into account the fact that some light sources do not have power spectral density functions (SPD) such that white-balance color correction based on a simple determination of the chromaticity of the illumination will approach "theoretical ideal" white balance color correction.
My conclusion is that it does, even though the single presentation of its use by the manufacturer I have so far looked at (the "Photoshop" version of their video) only hints at it.
The device (I describe it as "Barbie's eye shadow compact") includes three targets:
• A neutral gray target for making traditional white-balance color correction measurements.
• A "GretagMacbeth Colorchecker Classic" target, a pattern of numerous small patches of known reflective spectrum. My discussion here will concentrate on this.
• A target including various patches of nearly-neutral reflective color but not quite. Its purpose is to be used in post-processing to provide color correction that intentionally varies slightly from "theoretically-ideal" so as to "beautify" the subject's skin. (We have encountered this notion before in connection with one of Drew Strickland's products.)
The associated software allows us to use a shot of the second of these targets to build a camera profile (spoken of as a "DNG" color profile, although that may not be a meaningful description).
This profile describes the color response (in both luminance and chromaticity, I assume) at various places in the color space (that is, for the object colors of the patches), taking into account the illumination on the target.
Now, if we invoke this profile when processing a camera raw file, it will overcome inconsistencies in the camera's response across the color space, taking account of the illumination while it's at it, assuming that the illumination for the actual shot is the same as that used to shoot the target. (This is the same kind of thing we do with respect to the response of a printer when we construct a profile for it.)
The video mentions that of course, ideally this should be done separately for "various kinds of illumination" (tungsten, daylight, etc.), and the appropriate profile used when processing raw files for shots taken under that "type" of illumination.
But it would in fact seem advantageous, when dealing with "difficult" lighting situations (as those Asher so poignantly described for us in connection with his work at Colburn) to make such profiles on an "ad hoc" basis (for example, for shots to be taken on a certain region of the stage with a certain lighting setup in effect).
This does not require anything complicated in production - just shooting the ColorChecker target at a key spot on the stage for each scenario. The heavy lifting is done by the new X-Rite software during post.
Well, that's how it looks after about ten minutes' contemplation.
Best regards,
Doug