The Image Processing Histogram Display

The brightness histogram is located in the lower left corner of each front panel. This tool is very handy when making brightness and contrast correction to an image prior to transmission or after reception. The horizontal scale along the bottom of the graph indicates the 'brightness' of pixels. The vertical scale represents a count of the number of pixels in the image that have a particular brightness value.


 

Dark Image: Notice that most of the pixel value counts occur below the mid point of the intensity scale. The Image is also somewhat of low contrast. This image can be lightened using the brightness slider and the contrast stretched using the contrast control.


Light Image: This low contrast image appears too light and washed out, as few pixel counts show up in the 'dark' area in the lower half of the histogram scale. The image could be darkened by reducing the setting of the 'brightness' slider, and then further enhanced by increasing the contrast.


 

Low Contrast Image: This low contrast image appears washed out as the pixel value counts are clustered around the mid brightness point in the scale. There are very few counts in the dark or light areas of the brightness scale. Increasing the contrast produces the image below.


Corrected Image: Notice how the histogram of this 'corrected' image is somewhat 'bell' shaped. This is a typical brightness distribution often found in continuous tone images (not computer graphics). Images with a proper brightness distribution often fare better during SSTV transmission under poor s/n conditions