Hello everyone, I was working on image segmentation (k means clustering based on colors) and I chose the HSV colorspace to select all the non-blue parts.
Now, I saw that by converting an image from RGB to HSV all the colors change, I took a look at the imshow() documentation and I found out that in any case this function read the image as BGR. So, my first question is: is it the only function acting like that? Does the others read the image as HSV? (I hope so, else I dont find the sense of this colorspace)…
My second question is: why the opencv HSV range is different from the others (e.g the Gimp one), and is there any way to find the blue values without using python?
Have a good day!
your expectations were misplaced. work to discover your assumptions, make them explicit, and investigate why your expectations don’t match reality.
matrices (cv::Mat, numpy array) only know how many channels the contained data uses, not what color space it is.
OpenCV’s usual assumption is that 3-channel color data has BGR order and values.
imshow assumes that any 3-channel data is BGR. that goes for most other functions.
cvtColor must be told explicitly what to do.
if you need imshow to present data that is HSV, you need to cvtColor it into BGR, so that imshow can present it properly.
the point of the HSV space is that it makes some operations simpler.
the HSV hue value for uint8 (CV_8U) data obviously can’t be 0…359 degrees, because that exceeds the value range of an uint8 (0…255), so OpenCV maps the “hue angle” to 0…179.