Re: Identifying a rectangluar area made up of small dots (80%-20% screen)

[Przemek Klosowski]

On 11/03/2010 08:27 PM, Ian Journeaux wrote:
> In one of the analysis methods we are developing, I need to determine the
> location of a rectangular area that is made up of tiny dots in an image. In
> print terms it is a 20% to 80% screen. The area beterrn the dots is white
> the dots are black
>
> Once I have the area identified, I can perform the analysis on the image.
> Unfortunately right now finding the area to analyze takes as long as doing
> the analysis.
>
> Any thoughts on a technique that might be more efficient?

What technique did you use? For a known image like you seem to have, a 
convolution filter might work: if a is your grayscale image, and b is 
the pixel pattern of your area, conv2(a,b) should peak where your images 
overlap.