Roger, You need to measure a reference white under the same conditions. You will get Y (absolute value in cd/m2) for white, which you can use to normalize data with Y of White Point equal to 100. Knowing the WP will also enable you to convert from the measurement WP to a standard WP (D50, etc.) Danny www.babelcolor.com -----Message d'origine----- De : Colorsync-users [mailto:colorsync-users-bounces+dpascale=babelcolor.com@lists.apple.com] De la part de Roger Breton Envoyé : 1 août 2017 18:06 À : 'ColorSync' Objet : Convert CIE xyY to Photoshop D50/2 CIE Lab I been measuring flowers with one of my colorimeter. The petals of one such flower, lit by noon direct sunlight, gave me the following CIE xyY 1931/2 coordinates: CIE x = 0.3058 CIE y = 0.2053 CIE Y = 846 cd/m2 I took a picture of the flower and would like to use these coordinates as a guide for color correction. My question is how do I convert xyY to Photoshop's Lab? Not an easy problem, I know, that's why I turn to you guys for any help. Best / Roger