Removing hue and saturation ("desaturating") leads to a grayscale image with the same luminance as the original colors, for instance:
(source: my own photo)
It is not possible to remove hue alone without removing saturation, as any saturated color must be saturated in some direction (hue). Nor is it possible to "split" the image into HSV ...
https://alloyui.com/examples/color-picker/hsv.html - it would be the best for you to play a little with HSV color picker.
Problem of color picking with HSV boils down to 2D coordinates (H, S) with additional parameter V. Therefore, you are using H as x-axis value ans S as y-axis value. If you drop H and S (set them to 0), you basically have white color and ...
You can take a 1D Fourier transform of a row of pixels from the image; it will give you the horizontal frequencies present in that row.
You could sample one row out of the image, or else average all the rows together to get an overall picture of the horizontal frequencies.