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Photographic images are valuable data resources for studying long termchanges in the solar magnetic field and its influence on the Earth's climateand weather.  We digitized more than 100 years of white light images stored in photographicplates and films that are available at Kodaikanal observatory starting from1904. The digitized images were calibrated for relative plate density andaligned in such a way that the solar north is in upward direction. Asemi-automated sunspot detection technique was used to identify the sunspots onthe digitized images. In addition to describing the calibration procedure andavailability of the data, we here present preliminary results on the sunspotarea measurements and their variation with time. The results show that thewhite-light images have a uniform spatial resolution throughout the 90 years ofobservations. However, the contrast of the images decreases from 1968 onwards.The images are circular and do not show any major geometrical distortions. Themeasured monthly averaged sunspot areas closely match the Greenwich sunspotarea over the four solar cycles studied here. The yearly averaged sunspot areashows a high degree of correlation with the Greenwich sunspot area. Though themonthly averaged sunspot number shows a good correlation with the monthlyaveraged sunspot areas, there is a slight anti-correlation between the twoduring solar maximum The Kodaikanal data archive is hosted athttp://kso.iiap.res.in. The long time sequence of the Kodaikanal white lightimages provides a consistent data set for sunspot areas and other proxies. Manystudies can be performed using Kodaikanal data alone without requiringintercalibration between different data sources.

Digitized archive of the Kodaikanal images: Representative results of solar cycle variation from sunspot area determination