SRGB-aware image resize in Pillow

Question

Pillow's basic Image.resize function doesn't appear to have any options for SRGB-aware filtering. Is there a way to do SRGB-aware resizing in Pillow?

I could do it manually by converting the image to float and applying the SRGB transforms myself...but I'm hoping there's a built-in way.

Answer 1

I ended up implementing sRGB-aware resize myself using the following routine. It takes an 8-bit RGB image and a target size and resampling filter.

from PIL import Image
import numpy as np

def SRGBResize(im, size, filter):
    # Convert to numpy array of float
    arr = np.array(im, dtype=np.float32) / 255.0
    # Convert sRGB -> linear
    arr = np.where(arr <= 0.04045, arr/12.92, ((arr+0.055)/1.055)**2.4)
    # Resize using PIL
    arrOut = np.zeros((size[1], size[0], arr.shape[2]))
    for i in range(arr.shape[2]):
        chan = Image.fromarray(arr[:,:,i])
        chan = chan.resize(size, filter)
        arrOut[:,:,i] = np.array(chan).clip(0.0, 1.0)
    # Convert linear -> sRGB
    arrOut = np.where(arrOut <= 0.0031308, 12.92*arrOut, 1.055*arrOut**(1.0/2.4) - 0.055)
    # Convert to 8-bit
    arrOut = np.uint8(np.rint(arrOut * 255.0))
    # Convert back to PIL
    return Image.fromarray(arrOut)