How to do edge detection on a jpg file?

I = imread('E.jpg');
 imshow(I)
 BW1 = edge(I,'prewitt');
 BW2 = edge(I,'canny');
 figure;
 imshow(BW1)
 figure;
 imshow(BW2)

BW1 = edge(I,'prewitt'); - This shows error that I needs to be 2 - dimensional but I is already 2 - D I assume.

Answer 1

[Image Analyst]

It's probably color (3D). Convert to grayscale:

grayImage = rgb2gray(rgbImage);

Or, in hsv space

hsv= rgb2hsv(rgbImage);
hueImage = hsv(:,:,1);  % Now do edge() on hueImage

Or, extract one of the color channels:

% Extract the individual red, green, and blue color channels.
redChannel = rgbImage(:, :, 1);
greenChannel = rgbImage(:, :, 2);
blueChannel = rgbImage(:, :, 3);