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Click on the Image to Display Full Size Image
A Meade DSI I Color test image with resulting statistics for the Luminance, Red, Green and Blue color layers (statistics taken from Fits Liberator while opening the image's Fits layer files) overlayed on top of the image.
The image demonstrates that the 'Histogram' number displayed above the histogram graph window is the peak pixel value for the Luminance layer.
This 'Histogram' number is quite useful when imaging to determine if image saturation could be occuring. 65,535 is the maximum numberic value used to store pixel brightness data in the image file. If this number reaches 65,535, it is likely that image detail is being lost.
An image contains the greatest possible detail when it utilizes the full range of possible pixel values, from 0 for the darkest level possible to just below 65,535 for the brigthest level.
Note that for dim objects, it may not be possible to obtain the brightest level approaching 65,535. The goal then becomes to maximize the range that is achievable with the given equipment and conditions. Lengthening exposure time increases the histogram number and is the method to use to increase image detail, until the histogram number remains just below 65,535 (to avoid saturation and loss of detail due to clipping on this high end).
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