def sRGB2RGB(img):
    """ this function converts a sRGB img to  linear RGB values.
    
        It loops through each pixel, and apply a conversion to pass from sRGB to linear RGB value.
        
    
        :param img: image to analyze, in sRGB
        :type img: numpy.ndarray
        :return: image to analyze, in RGB
        :rtyipe: numpy.ndarray
    """
    newimg = []
    for row in img:
        thisrow = []
        for pixel in row:
            thispixel = []
            for value in pixel:
                if value / 255 <= 0.04045:
                    thispixel.append(value / (255 * 12.92))
                else:
                    thispixel.append(((value / 255 + 0.055) / 1.055) ** 2.4)
            thisrow.append(thispixel)
        newimg.append(thisrow)
    return newimg
