After some fiddeling around with pygame.image I got this to work.

I use pygame because I though I knew how to display an iamge there. It turns out I didn't. Well at least now I guess I do.

Later on I will propably switch to a different gui library. I'm thinking of Tkinter.

And here is the code:

from matplotlib import mlab as mlab
from rtlsdr import RtlSdr
import numpy as np
from PIL import Image
import time
import pygame

DISPLAY_WIDTH = 256
DISPLAY_HEIGHT = 200

sdr = RtlSdr()
# configure device
sdr.sample_rate = 2.4e6  # Hz
sdr.center_freq = 94.7e6  # Hz
sdr.freq_correction = 60   # PPM
sdr.gain = 'auto'


image = []


def get_data():
    samples = sdr.read_samples(16*1024)
    power, _ = mlab.psd(samples, NFFT=1024, Fs=sdr.sample_rate /
                        1e6)

    max_pow = 0
    min_pow = 10

    # search whole data set for maximum and minimum value
    for dat in power:
        if dat > max_pow:
            max_pow = dat
        elif dat < min_pow:
            min_pow = dat

    # update image data
    imagelist = []
    for dat in power:
        imagelist.append(mymap(dat, min_pow, max_pow, 0, 255))
    image.append(imagelist[round(len(
        imagelist)/2)-round(len(imagelist)/8): round(len(imagelist)/2)+round(len(imagelist)/8)])
    if len(image) > 200:
        image.pop(0)


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


pygame.init()
gameDisplay = pygame.display.set_mode((DISPLAY_WIDTH, DISPLAY_HEIGHT))
pygame.display.set_caption(f"DIY SDR")
clock = pygame.time.Clock()
background = pygame.Surface(gameDisplay.get_size())
background = background.convert()
background.fill((0, 0, 0))

game_quit = False

while not game_quit:

    gameDisplay.blit(background, (0, 0))

    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            game_quit = True

    get_data()
    outimage = np.array(image, np.ubyte)
    outimage = Image.fromarray(outimage, mode='L')
    outimage = outimage.convert('RGBA')
    strFormat = 'RGBA'
    raw_str = outimage.tobytes("raw", strFormat)
    surface = pygame.image.fromstring(raw_str, outimage.size, 'RGBA')
    gameDisplay.blit(surface, (0, 0))
    pygame.display.update()
    clock.tick(60)

pygame.quit()

try:
    pass
except KeyboardInterrupt:
    pass
finally:
    sdr.close()