Scaling a matrix or bgr values

Python
1

I am trying to multiply every pixel in a frame by a double.
However each pixel is. bgr and uint8

def scaleVideo(bgr_dataset, avgs, fit):
    print("Shape of bgr is ", bgr_dataset.shape);
    nframes = bgr_dataset.shape[0]
    #then Width, Height, 3 
    for f in range(0,nframes-1,1):
        print("Scaling frame ", f, "\r")
        cf = fit[f]
        a = avgs[f]
        scale = a / cf
        for y in range(0, bgr_dataset.shape[1],1):
            for x in range(0, bgr_dataset.shape[2], 1):
                b = bgr_dataset[f,y,x,0]
                g = bgr_dataset[f,y,x,1]
                r = bgr_dataset[f,y,x,2]
                b *= scale
                g *= scale
                r *= scale
                bgr_dataset[f,y,x,0] = b
                bgr_dataset[f,y,x,1] = g
                bgr_dataset[f,y,x,2] = r
    return bgr_dataset

This routine will take ‘forever’ to run.
However:

bgr_dataset[f,:,:,:] *= scale

Does not work.

How can i scale each pixel value and ensure the scaled value is rounded and bounded?