Hi. You don't need imnoise:
round(128+0.2)=128
with 0.1 and 0.2 like you didn't add any noise. Uniform noise with zero mean:
image = ones([512,512])*128;
A = -30;
B = 30;
matrix_uniform = A + (B-A)*rand(size(image));
noisy_image = image + matrix_uniform;
figure,
subplot(1,2,1)
imshow(noisy_image./255),
subplot(1,2,2)
imhist(uint8(noisy_image))