Why Do My Python WMS GetMap TIFF Files Show Different Pixel Values Than the Original?

I'm trying to download a TIFF file from a WMS server using Python, but the pixel value at a specific coordinate differs from the original file I downloaded from the website.

I use the following code to download the file via a WMS GetMap request:

PYTHONCopied
import requests
import numpy as np
import rasterio
from rasterio.transform import from_origin
from rasterio.transform import rowcol
from rasterio.merge import merge
from rasterio.plot import show
from pyproj import Transformer
import certifi
import ssl
import matplotlib.pyplot as plt

Layer = "warme_nachten_huidig"
minx=13588.806396509579
miny=306893.81943950325
maxx=277788.8063965096
maxy=612693.8194395032
map_width = "2642"
map_height = "3058"
bbox = (minx, miny, maxx, maxy)

def map_downloaden(bbox, width, height):
    # WMS Service URL and parameters
    ssl.SSLContext.verify_mode = ssl.VerifyMode.CERT_OPTIONAL

    # Define the WMS service URL
    wms_url = "https://apps.geodan.nl/public/data/org/gws/YWFMLMWERURF/kea_public/ows?"

    # Define the parameters for the GetMap request
    params = {
        "service": "WMS",
        "version": "1.3.0",
        "request": "GetMap",
        "layers": f"{Layer}",
        "styles": "",
        "crs": "EPSG:28992",
        "bbox": ','.join(map(str, bbox)),  # Bounding box in EPSG:28992
        "width": width,  # Width of the output image
        "height": height,  # Height of the output image
        "format": "image/geotiff"  # Requesting GeoTIFF format
    }

    # Make the request to the WMS server
    response = requests.get(wms_url, params=params, stream=True, verify=certifi.where())

    # Check if the request was successful
    if response.status_code == 200:
        with open(file_path_python, 'wb') as f:
            f.write(response.content)
        print(f"Map successfully downloaded to {file_path_python}")
    else:
        print(f"Failed to download map. Status code: {response.status_code}")

map_downloaden(bbox, map_width, map_height)

To compare the data, I extract the value at a given coordinate using this code:

PYTHONCopied
def get_coordinate_value(coord, file_path, versie):
    with rasterio.open(file_path) as dataset:

        # Transform geographic coordinates to the raster's CRS
        transformer = Transformer.from_crs("EPSG:4326", dataset.crs, always_xy=True)
        projected_coord = transformer.transform(coord[0], coord[1])
        # Transform geographic coordinates to raster's pixel coordinates
        row, col = rowcol(dataset.transform, projected_coord[0], projected_coord[1])

        # Ensure the calculated row and col are within the raster's dimensions
        if 0 <= row < dataset.height and 0 <= col < dataset.width:
            # Read the data value at the given pixel location
            data_value = dataset.read(1)[row, col]
            print(f"---- {versie}-------- Height: {dataset.height} Width: {dataset.width} ---- row: {row} col: {col} ---- COORDINATES: {coord} ---- VALUE: {data_value} ")
        else:
            print("Coordinates are out of the raster's bounds.")
coord = ( 5.975079577360298, 51.6954090242412)
get_coordinate_value(coord, file_path_python, "Python---")
get_coordinate_value(coord, file_path_original, "Original")

The output logs are as follows:

LOGCopied
---- Python----------- 
Height: 3058 Width: 2642 ---- row: 2006 col: 1820 ---- COORDINATES: (5.975079577360298, 51.6954090242412) ---- VALUE: 3 

---- Original--------- 
Height: 3058 Width: 2642 ---- row: 2006 col: 1820 ---- COORDINATES: (5.975079577360298, 51.6954090242412) ---- VALUE: 0.6150805354118347 

It appears that the WMS GetMap request is returning a rendered image where values may be processed (e.g., color-mapped or rescaled), while the original file shows the raw data. Is this behavior expected when using a WMS, and how can I retrieve the raw data values (perhaps using a different service like WCS or alternate parameters)?