Trouble with error from polyfit

I have written Matlab code to perform the following steps:

1) Read the original cottage picture.

2) Obtain its sizes.

3) Show the x values for the curve fitting.

4) Make a copy of the original picture.

5) Iterate through top 70 rows where the sky is. Use functions polyfit and .

6) Iterate through each color individually.

7) The polynomial approximation needs each row as a double vector.

8) Compute a synthetic row.

9) Put the row into the new sky.

10) End the loops

11) Show the new image.

12) Show the old image.

Here is the code:

function imageManip(imageName) 

inputImage = imread(imageName);
[sizeX,sizeY,~] = size(inputImage);
copyImage = inputImage; 
for r = 1:70
    for co = 1:3
        var1 = 1:sizeY;
        var2 = copyImage(r,:,co); 
        P = polyfit(var1,var2,2);
        Y = polyval(P,var1);
        copyImage(r,:,co) = Y; 
    end 
end 
imshow(copyImage);

end

When I run the code, the following errors appear:

Error using polyfit (line 68)
MTIMES (*) is not fully supported for integer classes. At least one argument must be
scalar.

Error in project2_1 (line 10)
        P = polyfit(var1,var2,2);

Can someone explain how I can fix this? Thanks.

Answer 1

[John D'Errico]

The pixels in an image are stored as uint8 (apparently in this case). Is that not what the error message effectively told you?

Convert to doubles to use polyfit.