Custom Color Palettes in geom_imshow()

The cmap parameter in geom_imshow() controls how greyscale images are colorized.

It accepts either a colormap name (e.g., ‘magma’) or a list of color codes. When a list is provided, pixel values are binned across the given colors. For smoother gradients, you can use the palette(n) method on any color scale to generate a larger palette.

from urllib.request import urlopen

import numpy as np
from rasterio.io import MemoryFile

from lets_plot import *

LetsPlot.setup_html()

# Load Mount Rainier shaded relief (georeferenced tiff).
# Source: https://pugetsoundlidar.ess.washington.edu/lidardata/restricted/filegeodatabase/mtrainierNP/index.html
memfile = MemoryFile(urlopen("https://pugetsoundlidar.ess.washington.edu/lidardata/restricted/filegeodatabase/mtrainierNP/peak.tif").read())
data = memfile.open()
crs, bounds = data.crs, data.bounds
print("{}\n{}".format(crs, bounds))

EPSG:26910
BoundingBox(left=591605.8273623086, bottom=5187196.672708434, right=596902.2082595474, top=5190956.943133966)

# Get the first band as a 2D numpy array.
image = data.read(1)
type(image), np.shape(image)

(numpy.ndarray, (1958, 2758))

extent = [bounds.left, bounds.right, bounds.bottom, bounds.top]

ggplot() + theme_void() + geom_imshow(image, extent=extent)