在Python中，将值-1分配给Mat文件中的数组会导致255

Question

When I print the following array, all the values are 255 instead of -1. Any ideas? I guess it has something to do with 8 bits, but I can't understand it. I want to assign the -1 value to all the values in the array. I know there are workarounds like creating a new array with same size, I don't want that, I want to understand the problem.

dados = scipy.io.loadmat('myDataset.mat')
ds_Y_Test = dados['Y']

for value in ds_Y_Test:
    value[0]=-1

Answer 1

-1 in two's complement binary is 11111111, which is 255 in unsigned binary, so that seems like a good guess! It looks like you've loaded as the data as uint8 - you will have to convert the array (eg with .astype ).