# Photometry using a DLSR camera

The C-Munipack software can decode RAW images produced by selected DSLR cameras. Because the DSLR cameras have not been designed to be used for the photometry, there are several potential pitfals that you may stumble upon. As in any other scientific work, it is recommended to be careful and to check if your results are correct before using or publishing them. In case of the ‘raw’ images, you should know, that the available documents on the ‘raw’ format are imcomplete, chaotic and often inconsistent.

## Color components

The most common mistake is that the color components are not in correct order. Almost all commercial DSLR cameras have a single array of light sensitive elements. Before the array, there is a color filter mosaic, most of them is a Bayer filter <http://en.wikipedia.org/wiki/Bayer_filter>. Color components are distributed in a repeating pattern:

    R  G  R  G  R  G  ...
    G  B  G  B  G  B  ...
    R  G  R  G  R  G  ...
    ...

The problem is, that in the first cell of the first row, some models have red (R) component and others starts with the blue (B) or green (G) component.

To check if the software decodes the components correctly I recommend to perform an easy test: take an image of any colorful object or objects that contain easily distinguished pathes of three basic colors (red, green and blue) on a black background. Save this image in the ‘raw’ format and load them into the C-Munipack software and perform Fetch/convert reduction steps with different selection of the color channel each time. After each conversion, show the resulting frame and check if the patches of the selected color component are bright and patches of other colors are dark.

See also

Bayer filter

  see http://en.wikipedia.org/wiki/Bayer_filter

RGB color components

  see http://en.wikipedia.org/wiki/Additive_color

RAW format

  see http://en.wikipedia.org/wiki/RAW_format