Digitization in Kodaikanal Observatory References and useful links : What is Digitization of an Image? Recording Image intensity through optics and rectangular array of sensing element (Figure 1) Dividing the image into a set of blocks i.e. pixels [sampling] (Figure 1) Each block being assigned an integer value representing image intensity [quantization] Kodaikanal Solar Image Archive Full disc images of Sun from the year 1904 in white light and different wavelengths [CaK ( nm), Hα ( nm)] are recorded in photographic plates and films. Different structures on Sun are visible from these images. Digitization Process Digital images are recorded through light source, imaging optics and sensing device (Figure 1) Using automated detection techniques we identify different solar structures (Figures 3,4,5) Automated detection are more accurate and less subjective. One can study the different solar phenomena. Digitization Process Charge Coupled Device Invented in 1969 at AT & T Bell labs Used as image sensor Based on semiconductor material Light intensity is converted to bulk of charge Collection of lenses Pixel size:15μm CCD size:4096х4096 Full Solar Disc Digital image of Sun in Hα (656.28nm) Figure 4: Center-to-boundary Figure 5: Automated Detection darkening corrected Image of filaments Figure 2: Digital Image of Full Solar Disc captured in Film Figure 1: Schematic of the digitization Solar Filament/ Prominence Filaments, on-disc dark elongated structures, are representative of magnetic activity on Sun. They can erupt (Figure 6) and have some impact on space weather. Kodaikanal data archive on filaments can act as a missing link for study of solar activity variation over large time span. Different parameters related to temporal periodicity can be extracted based on this historical data and can also be correlated with other dynamic phenomena of Sun such as sunspot cycle. Figure 6:Closer look at filaments/ Prominence (Image source: Solar Dynamics Observatory, NASA) Figure 3: Shift and rotation corrected image Keywords: Film: Used for photography. It is a sheet of transparent plastic base coated on one side with gelatine emulsion containing infinitesimally small light-sensitive silver halide crystals called grains. Size and other parameters of these grains determine resolution, contrast, light sensitivity. Imaging Optics: Lenses of different power arranged one after another with systematic interspacing for imaging the object on CCD plane with proper quality and magnification. Full Solar Disc: 2 dimensional view of the spherical shell at a radial distance of × 10 5 km from center of sun. Solar structures/features: Sunspots, filaments, active regions, flares, coronal mass ejections. Solar Cycle: Periodicity in time for different structures/features on sun with respect to their number/position. They help to understand dynamic phenomena happening in sun having impact on space climate. Poster Credit: Subhamoy Chatterjee