Compute average color of a JPEG image in CircuitPython

average_jpeg_color_code.py

# Compute the average (median or mean) color of a JPEG using ulab.numpy
# 9 Mar 2024 - @todbot / Tod Kurt
# Note: test images are included as comment below, max tested resolution 256x192
import ulab.numpy as np
import displayio
import jpegio

def rgb565_to_rgb888(v, swapped=True):
    """Convert RGB565 (normal or swapped) to RGB888 tuple"""
    if swapped:
        v = ((v & 0xff) << 8) | ((v >> 8) & 0xff)
    r8 = (v >> 11) << 3
    g8 = ((v >> 5) << 2) & 0xff
    b8 = (v << 3) & 0xff
    return r8, g8, b8

def bitmap565_to_nparray888(bitmap):
    """Turn a Bitmap in RGB565_SWAPPED colorspace to RGB888 ndarray"""
    w,h = bitmap.width, bitmap.height
    a = np.array(np.zeros((w*h,3)), dtype=np.int16)
    for y in range(h): 
        for x in range(w):
            a[y*w+x] = rgb565_to_rgb888(bitmap[x,y])
    return a

def average_color_for_jpeg(jpeg_fname):
    """For a given JPG file, determine most common color
    Returns both median (most common) and average as two RGB tuples"""
    decoder = jpegio.JpegDecoder()
    width, height = decoder.open(jpeg_fname)
    bitmap = displayio.Bitmap(width, height, 65535)  # RGB565_SWAPPED is 16-bit
    decoder.decode(bitmap)
    ndbitmap = bitmap565_to_nparray888(bitmap)
    med = np.median(ndbitmap, axis=0)
    avg = np.mean(ndbitmap, axis=0)
    rgb_median = int(med[0]),int(med[1]),int(med[2])
    rgb_mean = int(avg[0]),int(avg[1]),int(avg[2])
    return (rgb_median, rgb_mean)

jpeg_fnames = (
    "/imgs/test1.jpg",
    "/imgs/Mixed-forest-256.jpg",
    "imgs/Adirondacks_in_May_2008-256.jpg",
)

for jpeg_fname in jpeg_fnames:
    print("jpeg file:", jpeg_fname)

    rgb_median, rgb_avg = average_color_for_jpeg(jpeg_fname)
    print("median color: %02X%02X%02X" % rgb_median)
    print("average color: %02X%02X%02X" % rgb_avg)

 

The test images used: