{"id":1326,"date":"2015-06-04T16:01:24","date_gmt":"2015-06-04T20:01:24","guid":{"rendered":"https:\/\/blogs.mathworks.com\/steve\/?p=1326"},"modified":"2019-11-01T11:40:39","modified_gmt":"2019-11-01T15:40:39","slug":"image-region-filling-an-updated-design","status":"publish","type":"post","link":"https:\/\/blogs.mathworks.com\/steve\/2015\/06\/04\/image-region-filling-an-updated-design\/","title":{"rendered":"Image region filling – an updated design"},"content":{"rendered":"

About a year ago, I wrote a blog post<\/a> criticizing one of my functional designs from the 1990s, roifill<\/tt><\/a>. Now I have an update based on the R2015a release of Image Processing Toolbox.<\/p>

Let me show you an example to refresh your memory about roifill<\/tt>.<\/p>

I = imread('rice.png'<\/span>);\r\nimshow(I)\r\n<\/pre>\"\" 
You can use roifill<\/tt> to fill in pixels inside a region. (ROI in the function name stands for ''region of interest.'') You can specify the region interactively, using a mouse, or by providing the coordinates of a polygonal boundary, or by providing a binary mask. Here I'll provide the coordinates directly.<\/p>
x = [47 50 71 83 81 66 53 48];\r\ny = [102 110 110 103 92 92 97 102];\r\n\r\nJ = roifill(I,x,y);\r\nimshow(J)\r\n<\/pre>\"\" 
As I described in my earlier post<\/a>, the form of roifill<\/tt> that takes a mask image suffered from a design flaw. Most people would reasonably assume that the mask image would specify the set of pixel values that are to be filled. And that's the way I should have designed it. Unfortunately, though, roifill<\/tt> actually only fills the interior<\/b> pixels of the mask.<\/p>
Suppose your fill mask looked like this:<\/p>
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The function roifill<\/tt> only replaces these interior pixels of the mask:<\/p>
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The pixels on the edge of the mask are used to establish boundary conditions for the fill equation. Those pixels stay the same, which is not what most people expect.<\/p>
So how could we fix this problem? Changing the default behavior of roifill<\/tt> would be a significant incompatibility. But we have learned that optional behaviors often go undiscovered, so most people don't benefit from them.<\/p>
The Image Processing Toolbox team decided to address the problem by introducing a new function, regionfill<\/tt><\/a>, with the desired behavior. The function roifill<\/tt> remains in the product, so existing code that uses it will continue to work. Presumably, anyone currently using roifill<\/tt> with the mask syntax has already worked around its awkward behavior.<\/p>
At the bottom of the reference page for regionfill<\/tt>, there is a note that this function was introduced in R2015a.<\/p>
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And at the top of the reference page for roifill<\/tt>, there is a note encouraging the use of regionfill<\/tt>.<\/p>
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