Hello
I have a picture with some background noise: 
If you look closely you will see some small white spots in the gray area. I want to find the [x y] coordinate to transform the value at this position to NaN (not a number).
Can you please help me to do this?
I already have a idea but it is not really working:
First I check which color is the most frequently. Assume my picture is named Pic:
ImageData[Pic]
In my case I will see that {0.5333,0.5333,0.5333} is the most frequently.
So I will pick this color from my list:
RealBackgroundColor = ImageData[Pic][[2]][[1]]
The colors of the entire picture I get with this:
AllColorValues = ImageData[Pic][[2]];
The color values for my noise I will then get with:
NoiseColor = Cases[AllColorValues , Except[RealBackgroundColor ]]
Now I know the color values of my noise so I can start to find the [x,y] position of this color:
PositionOfNoise = PixelValuePositions[Pic, NoiseColor[[1]]]
Now I know the position of my noise. I can replace it with the number NaN or (just to visually check) with black color:
ReplacePixelValue[Pic, PositionOfNoise -> 0.0]
But as you can see here, this method is to sensitive:

I already tried to work with Interval but this also doesnt really work.
In Matlab this problem was handled very easy by my friend:
[x y]=find(background>4.67e4)
What would you do?
Peter Parker