Craig Owenby

Spatial Filtering Algorithm

To perform the spatial convolution/filtering operation, my algorithm first pads the image with the proper number of pixels on the top, bottom, left, and right. The padding colors are simply a reflection of the pixels on the edges. For each pixel in the original image, the neighborhood is taken from the padded image, with the filter being applied using vector dot products. Each dot product is added together, giving the value for the corresponding pixel in the output image.

for row=1:rows
    paddedRow = row + filterTop;
    for col=1:cols
        paddedCol = col + filterLeft;
        originalImage = 
            paddedImage(paddedRow - filterTop:paddedRow + filterTop, paddedCol - filterLeft:paddedCol + filterLeft,:);

    redVal = 0;
    greenVal = 0;
    blueVal = 0;

    % Performing dot product with filter for each row of the filter
    for filterRow=1:filterRows
       filterRowTranspose = reshape(filter(filterRow,:), filterCols, 1);
       redVal = redVal + originalImage(filterRow,:,1) * filterRowTranspose;
       greenVal = greenVal + originalImage(filterRow,:,2) * filterRowTranspose;
       blueVal = blueVal + originalImage(filterRow,:,3) * filterRowTranspose;
    end

    output(row, col,:) = [redVal, greenVal, blueVal];
end
    

Low Pass Filter

To make the low-frequency image, the program simply applies a Gaussian blur to the image.

% From the skeleton code
cutoff_frequency = 6;
filter = fspecial('Gaussian', cutoff_frequency*4+1, cutoff_frequency);

low_frequencies = my_imfilter(image1, filter);
    

Filtering Results

Identity Image	Blur Image	Large Blur Image
Sobel Image	LaPlacian Image	High Pass Image

High Pass Filter

To make the high-frequency image, the target image is first blurred using the same filter from the Low Pass Filter section. Then the low frequency image is then subtracted from the original image, leaving only the high frequencies.

high_frequencies = image2 - my_imfilter(image2, filter);
    

Hybrid Image

To create the hybrid image, the low-frequency image is simply added to the high-frequency image.

hybrid_image = low_frequencies + high_frequencies;