Error in image processing.

Hello, I made a program with the following code:

I = imread('ppc.png');
corners = detectFASTFeatures(I,'MinContrast',0.1);
J = insertMarker(I,corners,'circle');
imshow(J);

and shows me the following error

Error using vision.internal.detector.fast.parseInputs (line 4)
Expected I to be of size MxN when it is actually size 255x559x3.

Error in detectFASTFeatures>parseInputs (line 97)
    params = vision.internal.detector.fast.parseInputs(I, varargin{:});

Error in detectFASTFeatures (line 63)
params = parseInputs(I, varargin{:});

Error in zz (line 2)
corners = detectFASTFeatures(I,'MinContrast',0.1);

Answer 1

[Walter Roberson]

http://www.mathworks.com/help/vision/ref/detectfastfeatures.html

points = detectFASTFeatures(I) returns a cornerPoints object, points. The object contains information about the feature points detected in a 2-D grayscale input image, I.

You are not passing in a grayscale image, you are passing in a color image.

Answer 2

[Dima Lisin]

Hi Massimo,

As Walter pointed out, detectFASTFeatures takes a grayscale image. Please use rgb2gray to convert I to grayscale.

Answer 3

[Massimo Colavita]

Thanks. Another question, I want to detect circles in the image: Why I see the whole picture 3 blank? and How should I apply the function "Strel"?

I = imread('ppc.png');

gr = rgb2gray(I);
level = graythresh(gr);
bw = im2bw(gr, level);
figure, imshow(bw);
title(1)

bw2 = bwareaopen(bw, 200);
figure, imshow(bw2);
title(2)

bw3 = imfill(bw2, 'holes');
figure;
imshow(bw3);
title(3);