Image Processing Technique

in Japanese

IBM PC/AT convertible, OS: Windows

HPC-1 controller, CCDOPS, HIDDEN IMAGE, Picture Publisher, PhotoShop, StellaImage4.

1. Dark & Flat Frame:
High precision dark & flat frames are generated by combining many frames (8 to 32)

2. Maximum Entropy deconvolution Method (MEM)
MEM is used for the planet images and some of the planetary nebulae. For the stellar object, this may result in an 'unnatural' picture.

3. Hyperbolic conversion (named 'Digital Development' )
Define pixel level in the original image as x and that in its unsharpened image as y. We consider a conversion of image data by z=kx/(y+a), where k and a are scalar parameters. If a pixel level x is much lower than a, this conversion results in no change in the gamma curve of the image. If x is much larger than a, this conversion reduces the gradient of the gamma curve. Then, the gamma curve is converted in a hyperbolic form. The turnover point is x=a. At the same time, the edge enhancement effect will appear only in the low gradient regime. When the parameter a is chosen very carefully, this process results in an analogous effect to the chemical process of film. The Rosette Nebula in this gallery is almost indisguishable from its picture taken by the TP2415 film. This is the effect of Digital Development.

Example to show the effect of Digital Development Processing (M77 galaxy)
a) Conventional processing, b) Hyperbolic conversion of gamma curve, c) Hyperbolic conversion + edge enhancement
Detail of digital development

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Kunihiko OKANO

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