Sigma DP1 User Manual

The histogram is a graph depicting the distribution of brightness values in 
the image for each of the three color channels (Red, Green, and Blue). The 
horizontal axis shows the brightness level, with darker pixels towards the 
left side and brighter pixels toward the right.    The vertical axis shows the 
proportion of pixels at each level of brightness.     

By examining the histogram of the full image, you can gauge the overall 
exposure of that image.  You can also use the histogram to determine if 
zoomed-in sections of an image are over or under exposed. 

This histogram shows that the higher pixel 
values are never used in the image, indicating 
that the image is underexposed, and therefore 
will appear dark. In general, when the 
histogram is higher on the left side, the image 
is mostly composed of dark pixels, causing it to 
appear dark—either because the image is 
underexposed or because it is a dark scene 
such as night shot or sunset.

This histogram shows a fairly even distribution 
of pixel values, indicating that the image is well 
exposed, with good contrast. However, the 
histogram distribution of a well exposed image 
will vary greatly depending on the subject. 

This histogram shows that many of the pixel 
values are at their brightness limit, indicating 
that some areas of the image may be blown 
out. In general, when the histogram runs off the 
right side, the image will have many white 
pixels—either because the image is 
overexposed or because it is a bright scene 
such as the beach or snow.