cohist session 1
Contents
Original Image
filename = 'flowers4.png'; % filename = 'color_cube.jpg'; rgb = imread(filename); rgb = im2double(rgb); imshow(rgb);
Choose background region
uncomment for interactive specification
imshow(rgb); % [c r p] = impixel % save sess1 c r p load sess1 rect = [c(1)-15,r(1)-15,31,31]; hold on plot(c(1),r(1),'yo'); text(c(1)+20,r(1),'sample'); hold off
mean background rgb
xc = rgb(:,:,1) - 0.5*(rgb(:,:,2)+rgb(:,:,3));
yc = sqrt(3)/2*(rgb(:,:,2)-rgb(:,:,3));
cohist((xc+1)/2,(yc+1)/2,32,4);samp = imcrop(rgb,rect);
imshow(samp);
sz = size(samp);
mcolor = sum(sum(samp))/(sz(1)*sz(2));
mcolor = mcolor(:);
fprintf('rgb means: %g %g %g\n',mcolor);
rgb means: 0.38768 0.586432 0.293126
color distance from background
dev = sqrt((rgb(:,:,1)-mcolor(1)).^2+(rgb(:,:,2)-mcolor(2)).^2+(rgb(:,:,3)-mcolor(3)).^2); imshow(dev);
imhist(dev);
BW = im2bw(dev,0.6);
% imshow(BW);
imshow(cat(3,rgb(:,:,1).*BW,rgb(:,:,2).*BW,rgb(:,:,3).*BW));
rgb co-histograms
subplot(2,2,1); imshow(rgb); subplot(2,2,2); cohist(rgb(:,:,1),rgb(:,:,2)); xlabel('red channel'); ylabel('green channel'); subplot(2,2,3); cohist(rgb(:,:,1),rgb(:,:,3)); xlabel('red channel'); ylabel('blue channel'); subplot(2,2,4); cohist(rgb(:,:,2),rgb(:,:,3)); xlabel('green channel'); ylabel('blue channel');
xyv co-histograms
xc = rgb(:,:,1) - 0.5*(rgb(:,:,2)+rgb(:,:,3)); yc = sqrt(3)/2*(rgb(:,:,2)-rgb(:,:,3)); zc = (rgb(:,:,1)+rgb(:,:,2)+rgb(:,:,3))/3; subplot(2,2,1); imshow(rgb); subplot(2,2,2); cohist((xc+1)/2,(yc+1)/2); xlabel('chroma x'); ylabel('chroma y'); subplot(2,2,3); cohist(zc,(xc+1)/2); xlabel('value'); ylabel('chroma x'); subplot(2,2,4); cohist(zc,(yc+1)/2); xlabel('value'); ylabel('chroma y');
close subplot(2,2,1); imshow(rgb); title('original image'); subplot(2,2,2); imshow((xc+1)/2); title('chroma x: red - cyan colors'); subplot(2,2,3); imshow((yc+1)/2); title('chroma y: green - blue colors'); subplot(2,2,4); imshow(zc); title('value');
ad-hoc chroma selection
close
bw4 = and(xc>-0.4,xc<0.6);
bw5 = and(yc>0.1,yc<0.5);
bw6 = ~(bw4&bw5);
%imshow(bw5&bw4);
subplot(1,1,1);
imshow(cat(3,rgb(:,:,1).*bw6,rgb(:,:,2).*bw6,rgb(:,:,3).*bw6));
show saturated hues at normal value
hsv = rgb2hsv(rgb);
t1 = hsv(:,:,1);
t2 = ones(size(t1));
t3 = hsv(:,:,3);
rgb2 = hsv2rgb(cat(3,t1,t2,t3));
imshow(rgb2);
title('saturated hues at normal value');
show saturated hues at full value
rgb3 = hsv2rgb(cat(3,t1,t2,t2));
imshow(rgb3);
title('saturated hues at full value');
hue histogram
imhist(t1);
title('hue histogram');
xc = rgb3(:,:,1) - 0.5*(rgb3(:,:,2)+rgb3(:,:,3)); yc = sqrt(3)/2*(rgb3(:,:,2)-rgb3(:,:,3)); cohist((xc+1)/2,(yc+1)/2); title('saturated hues at full value'); xlabel('chroma x'); ylabel('chroma y');
trun1 = round(8*hsv(:,:,1))/8; trun2 = round(4*hsv(:,:,2))/4; trun3 = round(8*hsv(:,:,3))/8; rgb4 = hsv2rgb(cat(3,trun1,trun2,trun3)); imshow(rgb4);
g = (trun3*8+trun2*32+trun1*256)/256; imshow(g);
imhist(g);
bw1 = ~and(g<0.5,g>0.3); imshow(bw1);
imshow(cat(3,rgb(:,:,1).*bw1,rgb(:,:,2).*bw1,rgb(:,:,3).*bw1));
