Correlation pattern for lysozyme by assuming the intensity of the incident X-rays Ii = 5 × 1021 photons pulse−1 mm−2. (a) Correlation pattern of equation (6) for a pair of two-dimensional experimental intensity patterns obtained from an identical two-dimensional theoretical intensity pattern but with different sets of random numbers for the Poisson distribution. A high correlation line is observed extending from the origin towards the direction of . The high correlation line fades at a certain value of k because of the quantum noise. (b) Correlation pattern of equation (8), which is obtained by averaging the pattern shown in (a) over the quantum noise. Because of the suppressed quantum noise, the high correlation line is now observed extending to high k values. (c) When the directions of the beam axes are significantly different in a pair of two-dimensional intensity patterns, the high correlation line is absent. In this and subsequent figures (Figs. 2, 4 and 8), unlike in Fig. 1, both the abscissa and ordinate are taken to be proportional to k. In this case, the area in the figures is also proportional to that on the curved Ewald spheres (Lambert's azimuthal equal-area projection).