Estimate Brightness of an image Opencv

Question

I have been trying to obtain the image brightness in Opencv, and so far I have used calcHist and considered the average of the histogram values. However, I feel this is not

Answer 1

I was about to ask the same, but then found out, that similar question gave no satisfactory answers. All answers I've found on SO deal with human observation of a single pixel RGB vs HSV.

From my observations, the subjective brightness of an image also depends strongly on the pattern. A star in a dark sky may look more bright than a cloudy sky by day, while the average pixel value of the first image will be much smaller.

The images I use are grey-scale cell-images produced by a microscope. The forms vary considerably. Sometimes they are small bright dots on very black background, sometimes less bright bigger areas on not so dark background.

My approach is:

• Find histogram maximum (HMax) using threshold for removing hot pixels.
• Calculate mean values of all pixel between HMax * 2/3 and HMax

The ratio 2/3 could be also increased to 3/4 (which reduces the range of pixels considered as bright).

The approach works quite well, as different cell-patterns with same titration produce similar brightness.

P.S.: What I actually wanted to ask is, whether there is a similar function for such a calculation in OpenCV or SimpleCV. Many thanks for any comments!