Good morning everybody! I created a physically accurate scene and my aim is to study radiometric conditions over the rendered scene in order to obtain an illumination map in terms of [W/m^2]. I saved images in OpenEXR file format, due to its high dynamic-range properties and I wanted to obtain a Relative Luminance Map starting from RGB values in “R” “G” “B” channels. The major issue is how to scale linear values from OpenEXR channels to have physically accurate values between [0, 1], needed to obtain Relative Luminance map maintaining the HDR properties of the file format. Part of the code is reported below.
pt = Imath.PixelType(Imath.PixelType.FLOAT) exrfile = exr.InputFile(filename) dw = exrfile.header()['dataWindow'] size = (dw.max.x - dw.min.x + 1, dw.max.y - dw.min.y + 1) redstr = exrfile.channel('R', pt) red = np.fromstring(redstr, dtype = np.float32) red.shape = (size, size) # Numpy arrays are (row, col) greenstr = exrfile.channel('G', pt) green = np.fromstring(greenstr, dtype = np.float32) green.shape = (size, size) # Numpy arrays are (row, col) bluestr = exrfile.channel('B', pt) blue = np.fromstring(bluestr, dtype = np.float32) blue.shape = (size, size) # Numpy arrays are (row, col) rel_luminance = 0.2126*red[:,:]+0.7152*green[:,:]+0.0722*blue[:,:]
For a test image the obtained Max values of the three channels are respectively:
Max(R) = 198.16421508789062
Max(G) = 173.5792999267578
Max(B) = 163.20120239257812
The obtained values are obviously not in the range between [0, 1], moreover I am not able to understand the global maximum value to scale the channels and obtain what i want.
Has someone some tips to solve my problem? Thanks in advance.