QPcard 101 v4 Greyscale Cards (Pack of 3 cards). Qpcard 101 v4 is the new improved version of Qpcard 101. It has three patches with perfectly neutral dark gray, mid gray and white colors. The Cie L*a*b values are 35*0*0, 48*0*0 and 95*0*0. The spectral respons of the three colors is almost perfect straight, meaning there will be no problems with metamerism at all. The colors are extremely fade resistant. The main purpose with the card is to use the gray patch for neutral gray balancing of the image. The gray patch is reflecting 18 % of the light, making it useful also for exposure purposes. Since the white patch is free from fluorescent whitening agents, it is perfect for custom white balance setting of your camera before shooting. There is a millimeter reference scale on the card. The card is self-adhesive making it perfect to place on almost any surface in the subject.