How to remove error "Integers can only be combined with integers of the same class, or scalar doubles."

When I'm using typecasting my image quality is affected and I'm not getting desired results. Here is my code:

clc
[file path]=uigetfile('*.*');
img=imread(file);
[r c p]=size(img);
[pl1 pl2 pl3 pl4 pl5 pl6 pl7 pl8]=bitplane_slice(img);
figure;
subplot(3,3,1);imshow(pl1);title('pln 1')
subplot(3,3,2);imshow(pl2);title('pln 2')
subplot(3,3,3);imshow(pl3);title('pln 3')
subplot(3,3,4);imshow(pl4);title('pln 4')
subplot(3,3,5);imshow(pl5);title('pln 5')
subplot(3,3,6);imshow(pl6);title('pln 6')
subplot(3,3,7);imshow(pl7);title('pln 7')
subplot(3,3,8);imshow(pl8);title('pln 8')

    sec=imread('ab.png');
    new_sec=imresize(sec,[r c]);
    stego = new_sec+pl2*2+pl3*4+pl4*8+pl5*16+pl6*32+pl7*64+pl8*128;
    figure;
    subplot(1,2,1);imshow(new_sec);title('Sec image')
    subplot(1,2,2);imshow(uint8(stego));title('Stego image')

    [pl1 pl2 pl3 pl4 pl5 pl6 pl7 pl8]=bitplane_slice(stego);
    figure;
    subplot(3,3,1);imshow(pl1);title('pln 1')
    subplot(3,3,2);imshow(pl2);title('pln 2')
    subplot(3,3,3);imshow(pl3);title('pln 3')
    subplot(3,3,4);imshow(pl4);title('pln 4')
    subplot(3,3,5);imshow(pl5);title('pln 5')
    subplot(3,3,6);imshow(pl6);title('pln 6')
    subplot(3,3,7);imshow(pl7);title('pln 7')
    subplot(3,3,8);imshow(pl8);title('pln 8')

Answer 1

[Image Analyst]

Because you're essentially adding two images with the least significant bit of one zeroed out, you're most likely going to get overflow which, for a uint8 image, means that you'll clip at 288. Cast everything to double before summing to avoid the error.

[Walter Roberson]

clip at 255 rather than 288

[ROMIL]

Typecasting to double isn't helping. How can I clip it at 255?

[Walter Roberson]

Usually in steganography, you only insert the hidden message into one bit plane, at most 4 bit planes, and you overwrite the existing information in those planes instead of creating an arithmetic sum of the old image and the hidden message.

[Image Analyst]

Yeah, you're not really doing steganography - you're merely doing watermarking . Nothing is really hidden or encrypted. You're putting it right there in plain sight.

Anyway, your question doesn't make sense. Like I said you're already clipping, but clipping is not something people usually want - it's something they try to avoid .

[ROMIL]

Well I can overwrite the existing plane, but still need to merge all the bit planes, can you provide me a better alternative to arithmetic sum?

[Image Analyst]

See my LSB watermarking demo, attached below in blue.