matplotlib.image.imread(): Some images are integers while some others are floats

I am trying a script that works with images in python.The first image was working and the second one did not work at all.

The script was

import matplotlib.pyplot as pltimport matplotlib.image as mpimgimport numpy as npimage = mpimg.imread('test.jpg')# Grab the x and y size and make a copy of the imageysize = image.shape[0]xsize = image.shape[1]color_select = np.copy(image)# Define color selection criteria###### MODIFY THESE VARIABLES TO MAKE YOUR COLOR SELECTIONred_threshold = 200green_threshold = 200blue_threshold = 200######rgb_threshold = [red_threshold, green_threshold, blue_threshold]# Do a boolean or with the "|" character to identify# pixels below the thresholdsthresholds = (image[:,:,0] < rgb_threshold[0]) \            | (image[:,:,1] < rgb_threshold[1]) \            | (image[:,:,2] < rgb_threshold[2])color_select[thresholds] = [0,0,0]plt.imshow(color_select)

Then I discovered the reason why the second image did not work

print("Red channel - Min:", np.min(image[:,:,0]), "Max:", np.max(image[:,:,0]))print("Green channel - Min:", np.min(image[:,:,1]), "Max:", np.max(image[:,:,1]))print("Blue channel - Min:", np.min(image[:,:,2]), "Max:", np.max(image[:,:,2]))

For the first image

Red channel - Min: 0 Max: 255Green channel - Min: 10 Max: 255Blue channel - Min: 0 Max: 255

For the second image that did not work

Red channel - Min: 0.0 Max: 1.0Green channel - Min: 0.0 Max: 1.0Blue channel - Min: 0.0 Max: 1.0

Can someone explain to me the basics of why some images use 0-255 and other 0.0 to 1.0?