International
Tables for
Crystallography
Volume F
Crystallography of biological macromolecules
Edited by M. G. Rossmann and E. Arnold

International Tables for Crystallography (2006). Vol. F, ch. 11.2, p. 212   | 1 | 2 |

Section 11.2.3. Methods of integration

A. G. W. Lesliea*

aMRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, England
Correspondence e-mail: andrew@mrc-lmb.cam.ac.uk

11.2.3. Methods of integration

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There are two quite distinct procedures available for determining the integrated intensities: summation integration and profile fitting. Summation integration involves simply adding the pixel values for all pixels lying within the area of a spot, and then subtracting the estimated background contribution to the same pixels. Profile fitting (Diamond, 1969[link]; Ford, 1974[link]; Rossmann, 1979[link]) assumes that the actual spot shape or profile is known (in two or three dimensions) and the intensity is derived by finding the scale factor that, when applied to the known (or standard) profile, gives the best fit to the observed spot profile. In practice, profile fitting requires two separate steps: the determination of the standard profiles and the evaluation of the profile-fitting intensities. As will be shown later, profile fitting results in a reduction in the random error associated with weak intensities, but offers no improvement for very high intensities.

References

Diamond, R. (1969). Profile analysis in single crystal diffractometry. Acta Cryst. A25, 43–55.
Ford, G. C. (1974). Intensity determination by profile fitting applied to precession photographs. J. Appl. Cryst. 7, 555–564.
Rossmann, M. G. (1979). Processing oscillation diffraction data for very large unit cells with an automatic convolution technique and profile fitting. J. Appl. Cryst. 12, 225–238.








































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