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

From: Przemek Klosowski
Subject: Re: Identifying a rectangluar area made up of small dots (80%-20% screen)
Date: Thu, 04 Nov 2010 15:06:17 -0400
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv: Gecko/20100921 Fedora/3.1.4-1.fc13 Lightning/1.0b2 Thunderbird/3.1.4

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.

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