Pixel manipulation in Numpy

Question

I want to convert all pixel values 0 instead of the value of 255. Pixel values are kept in Numpy array, namely x and:

x.shape = (100, 1, 256, 256)

How to manipulate arrays with the condition?

I tried the below but the error occured "ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()"

i=0
for i in x[i]:
    if x[i]==255:
        x[i] = x[i]
    else:
        x[i] ==0

Answer 1

Just use:

x[x==255] = 0

Test:

# Repeatable randomness
np.random.seed(42)

# Synthesise array
x = np.random.randint(0,256, (100, 1, 256, 256), np.uint8)

# Count number of 255s
len(np.where(x==255)[0])    # result = 25671

# Make each 255 into 0
x[x==255] = 0

# Count number of 255s
len(np.where(x==255)[0])    # result = 0