how to detect edges in an image having only red object

Question

I have an image, in that image all red objects are detected.

Here's an example with two images:

http://img.weiku.com/waterpicture/2011/10/30/18/road_Traffic_signs_634577283637977297_4.jpg

But when i proceed that image for edge detection method i got the output as only black color. However, I want to detect the edges in that red object.

r=im(:,:,1); g=im(:,:,2); b=im(:,:,3);
diff=imsubtract(r,rgb2gray(im));
bw=im2bw(diff,0.18);
area=bwareaopen(bw,300);
rm=immultiply(area,r);  gm=g.*0;  bm=b.*0;
image=cat(3,rm,gm,bm);
axes(handles.Image);
imshow(image);

I=image;
Thresholding=im2bw(I);

axes(handles.Image);
imshow(Thresholding)

fontSize=20;
edgeimage=Thresholding;
BW = edge(edgeimage,'canny');
axes(handles.Image); 
imshow(BW);

Please show us the original, unmodified image. Also don't use `image` as a variable name its a builtin function. Thanks! — Benoit_11, Apr 28 '15 at 14:37
http://img.weiku.com/waterpicture/2011/10/30/18/road_Traffic_signs_634577283637977297_4.jpg — bk sumedha, Apr 28 '15 at 14:42
These are some example images.I am mainly concentrating on the sign boards. — bk sumedha, Apr 28 '15 at 14:43

Benoit_11 · Accepted Answer · 2015-04-28T14:53:40.513

8

When you apply im2bw you want to use only the red channel of I(i.e the 1st channel). Therefore using this command:

Thresholding =im2bw(I(:,:,1));

for example yields this output:

enter image description here

edited Apr 28 '15 at 14:53

answered Apr 28 '15 at 14:52

Benoit_11

13,785
2
22
35

2

Haha so simple. I was about to apply some serious morphology on that bad boy. +1. – rayryeng Apr 28 '15 at 14:53
What does im2 specifies?? – bk sumedha Apr 28 '15 at 14:54
yes sorry I changed the variable names to fit with yours :) – Benoit_11 Apr 28 '15 at 14:57
Great! If this helped please consider accepting the answer by clicking the checkmark beside it. Thanks! – Benoit_11 Apr 28 '15 at 15:01
From the ouput what i got, what features can i detect for further classification like which sign board it is??? – bk sumedha Apr 28 '15 at 15:12
That's an interesting question. I think you should post that as a new question so you will likely get the attention of more people and obtain more/high quality answers. Don't forget to specify what you have tried and post some code to show your effort. Cheers! – Benoit_11 Apr 28 '15 at 15:15
1

it's annoying how simple the answer turned out to be.. +1 – bilaly Apr 28 '15 at 16:39

score 0 · Answer 2 · edited May 23 '17 at 12:33

Just FYI for anyone else that manages to stumble here. The HSV colorspace is better suited for detecting colors over the RGB colorspace. A good example is in gnovice's answer. The main reason for this is that there are colors which can contain full 255 red values but aren't actually red (yellow can be formed from (255,255,0), white from (255,255,255), magenta from (255,0,255), etc).

I modified his code for your purpose below:

cdata = imread('roadsign.jpg');

hsvImage = rgb2hsv(cdata);         %# Convert the image to HSV space
hPlane = 360.*hsvImage(:,:,1);     %# Get the hue plane scaled from 0 to 360
sPlane = hsvImage(:,:,2);          %# Get the saturation plane
bPlane = hsvImage(:,:,3);          %# Get the brightness plane

% Must get colors with high brightness and saturation of the red color
redIndex = ((hPlane <= 20) | (hPlane >= 340)) & sPlane >= 0.7 & bPlane >= 0.7;

% Show edges
imshow(edge(redIndex));

Output: enter image description here

how to detect edges in an image having only red object

2 Answers2