Video Linear Filtering

Filtering is a technique for modifying or enhancing an image. For example, you can filter an image to emphasize certain features or remove other features.

Filtering is a neighborhood operation, in which the value of any given pixel in the output image is determined by applying some algorithm to the values of the pixels in the neighborhood of the corresponding input pixel. A pixel’s neighborhood is some set of pixels, defined by their locations relative to that pixel.

Linear filtering is filtering in which the value of an output pixel is a linear combination of the values of the pixels in the input pixel’s neighborhood.

Linear filtering of an image is accomplished through an operation called convolution. In convolution, the value of an output pixel is computed as a weighted sum of neighboring pixels. The matrix of weights is called the convolution kernel, also known as the filter.

Image processing operations implemented with convolution include smoothing, sharpening, and edge enhancement.


The operation called correlation is closely related to convolution. In correlation, the value of an output pixel is also computed as a weighted sum of neighboring pixels. The difference is that the matrix of weights, in this case called the correlation kernel, is not rotated during the computation.

Both can be performed using the toolbox function imfilter. This example filters an image with a
5-by-5 filter containing equal weights. Such a filter is often called an averaging filter.

I = imread('coins.png');
h = ones(5,5) / 25;
I2 = imfilter(I,h);
imshow(I), title('Original Image');
figure, imshow(I2), title('Filtered Image')

In Videos:

fin = 'rawVideo.avi'; fout = 'test.avi'; fileinfo = aviinfo(fin); nframes = fileinfo.NumFrames; aviobj = avifile(fout, 'compression', 'none', 'fps',fileinfo.FramesPerSecond); for i = 1:20 %Read frames from input video mov_in = aviread(fin,i); im_in = frame2im(mov_in); %Do processing on each frame of the video
%----------------------------------------------------------------------
%In this example - Linear Filters
h = ones(5,5) / 25;
im_out = imfilter(im_in,h);
%----------------------------------------------------------------------
%Write frames to output video frm = im2frame(im_out); aviobj = addframe(aviobj,frm); %i %Just to display frame number end; %Don't forget to close output file aviobj = close(aviobj); msgbox('DONE'); return;


Results