2.2	CALCULATING THE PRIMARY IMAGES
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		Recording the input images
		The standard input for CIP calculations consists of 18 rotation images, 2 or 4 tilt images and a circular polarization image: the rotation images are a series of images with incremental relative rotation of the thin section with respect to the polarizers and the lambda plate (typically using a fixed interval of 10°), the tilt images are captured with the thin section tilted about the N-S and E-W axes. For the circular polarization image, crossed polarizers and two quarter-lambda plates (above and below the thin section) are used. 18 rotation images at 10° intervals and 2 tilt images are the absolute minimum; routinely, one circular polarization image is included. Placing the input images in a stack (a multi-image sequence within NIH Image) and using the "Lazy stack" macro (appandix A2), the images are registered. We can think of them as a multichannel image in which, for each pixel , the following information is stored: (a) the grey level, G(0), G(10)... G(170), for 18 different orientations, (b) 2 or 4 greylevels which - when compared to the greylevel G(0), yield an information concerning whether the c-axis points above or below the thin section, and (c) a grey level indicative of the c-axis inclination w/r to the plane of the thin section. Additional images may be taken with parallel polarizers to obtain an image of dust and scratches for masking purposes (see later), or one without the thin section in place in order to be able to correct uneven lighting.       Left, from top to bottom: - 18 rotation images - 4 tilt images - 1 circular polarization image