# [argyllcms] Re: negative primaries

*From*: Elle Stone <l.elle.stone@xxxxxxxxx>*To*: argyllcms@xxxxxxxxxxxxx*Date*: Fri, 11 Jun 2010 05:50:04 -0400

On 6/10/10, Graeme Gill <graeme@xxxxxxxxxxxxx> wrote: > Given a bunch of real cameras, I wonder how common it is > for the cameras spectrum locus to fall outside the standard > observer spectrum locus, when the matrix has been created by > minimizing the (say) sum of squared errors of a representatively > weighted basket of real world color spectra. The "standard observer spectrum locus" means the horse-shoe-shaped outer boundaries of the CIE 1931 color space chromaticity diagram? And any negative primaries in the camera matrix are definitely outside the standard observer spectrum locus? The 360+ camera matrices used by dcraw, mostly but not all supplied by Adobe in the form of "camera coefficients", were presumably created from target shots by "minimizing the sum of squared errors" (there is code in dcraw for doing such from a ColorChecker chart, but Dave also takes it8 target shots for new cameras). I turned the the dcraw camera coefficients into camera matrices. They all have at least 2 negative primaries, a few have 4 negative primaries. All of them have negative green Z primaries (average -0.32588). Most of them have negative blue Y primaries (average -0.17736). If anyone is curious, you can download my dcraw camera matrix spreadsheet from http://www.dustystones.com/2010/photo-essays/negative-primaries/dcrawV899-camera-coefficients.ods. These matrices are relative to D65, not D50, but having done the chromatic adaptation for a few matrices, the value change is not that great - the negative numbers are still going to be negative. Regards, Elle Stone

**References**:**[argyllcms] negative primaries***From:*Elle Stone

**[argyllcms] Re: negative primaries***From:*Graeme Gill

**[argyllcms] Re: negative primaries***From:*Gerhard Fuernkranz

**[argyllcms] Re: negative primaries***From:*Graeme Gill

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