Blue colour range in hsv saturation system?

I'm trying to increase the intensity of blue pixels in an RGB image and I'm trying to increase the blue only pixel intensity, for example if I have:

imghsv=rgb2hsv(img);
imgs=imghsv(:,:,2);

I roughly set a condition for the blue range

imgs(ii,jj) >0.1 && imgs(ii,jj)<0.4

but I found out some yellow pixels are also enhanced.

I think I might missing something, is there another way where I can enhance the blue colours only in an image?

Thanks!

Answer 1

[Guillaume]

Hum!, the Hue channel (the one that contains the colour information) in a HSV image is the first one.

The limits of the blue hue depends on what you call blue, but it's in the region of 0.5 to 0.7.

So:

imghsv=rgb2hsv(img);
imgh=imghsv(:,:,2);
bluepixels = imgh >= 0.5 & imgh <= 0.7;

The saturation (2nd channel) is completely independent of the hue. You may want to filter pixels with very low saturation as they'll look almost black but it certainly won't help filtering out yellow (or green, or red, or any other colour)

[Yuchun Ding]

aha thanks for this to sum up, I used hsvimg(:,:,1) to find the range and increased the values in hsvimg(:,:,2)

Answer 2

[Walter Roberson]

I think you should be looking at 1/2 to 3/4 at least, perhaps a bit wider around that range

Invoke

colormapeditor

and use the Tools menu to select HSV colormap and look at the range of values.

[Yuchun Ding]

thanks a lot! it's really helped me to located many different colour range!