Python, OpenCV: Increasing image brightness without overflowing UINT8 array

Question

I am trying to increase brightness of a grayscale image. cv2.imread() returns a numpy array. I am adding integer value to every element of the array. Theoretica

Answer 1

I ran into a similar issue, but instead of addition, it was scaling image pixels in non-uniform manner.

The 1-D version of this:

a=np.array([100,200,250,252,255],dtype=np.uint8)
scaling=array([ 1.1,  1.2,  1.4,  1.2,  1.1])
result=np.uint8(a*scaling)

This gets you the overflow issue, of course; the result:

array([110, 240,  94,  46,  24], dtype=uint8)

The np.where works:

result_lim=np.where(a*scaling<=255,a*scaling,255)

yields result_lim as:

array([ 110.,  240.,  255.,  255.,  255.])

I was wondering about timing, I did this test on a 4000 x 6000 image (instead of 1D array), and found the np.where(), at least for my conditions, took about 2.5x times as long. Didn't know if there was a better/faster way of doing this. The option of converting to float, doing the operation, and then clipping as noted above was a bit slower than the np.where() method.

Don't know if there are better methods for this.