How to fast change image brightness with python + OpenCV?

Question

I have a sequence of images. I need to average brightness of these images.

First example (very slow):

img = cv2.imread(\'test.jpg\')         


        

Answer 1

You can use this function to change your desired brightness or contrast using C++ just like the same way you do it on photoshop or other similar photo editing software.

def apply_brightness_contrast(input_img, brightness = 255, contrast = 127):
    brightness = map(brightness, 0, 510, -255, 255)
    contrast = map(contrast, 0, 254, -127, 127)

    if brightness != 0:
        if brightness > 0:
            shadow = brightness
            highlight = 255
        else:
            shadow = 0
            highlight = 255 + brightness
        alpha_b = (highlight - shadow)/255
        gamma_b = shadow

        buf = cv2.addWeighted(input_img, alpha_b, input_img, 0, gamma_b)
    else:
        buf = input_img.copy()

    if contrast != 0:
        f = float(131 * (contrast + 127)) / (127 * (131 - contrast))
        alpha_c = f
        gamma_c = 127*(1-f)

        buf = cv2.addWeighted(buf, alpha_c, buf, 0, gamma_c)

    cv2.putText(buf,'B:{},C:{}'.format(brightness,contrast),(10, 30), cv2.FONT_HERSHEY_SIMPLEX, 1, (0, 0, 255), 2)
    return buf

def map(x, in_min, in_max, out_min, out_max):
    return int((x-in_min) * (out_max-out_min) / (in_max-in_min) + out_min)

After that you need to call the functions by creating trackbar using cv2.createTrackbar() and call that above functions with proper parameters as well. In order to map the brightness values which ranges from -255 to +255 and contrast values -127 to +127, you can use that map() function. You can check the full details of about python implementation here.