Adding Vignetting Effect to Images

When the lens size is smaller than the dimensions of the actual image sensor, or inadequately covering it, it leads to an effect whereby the center of the image is clear, and a fading/darkening of the image borders is seen. This effect is commonly referred to as the Vignetting Effect. In graphics, it is used to de-emphasize the distracting background, and shed light on the foreground objects.

Example

Scale factor at image border=1.0	Scale factor at image border=0.8	Scale factor at image border=0.6
Scale factor at image border=0.4	Scale factor at image border=0.2	Scale factor at image border=0.1

MATLAB Code

% *************************************************************************
% Title: Function-Introduce Vignetting effect to the image
% Author: Siddhant Ahuja
% Created: September 2008
% Copyright Siddhant Ahuja, 2008
% Inputs: Input Image (var: inputImage), Scale Change level (var:
% scaleLevel) Valid values for scale change should go from 0.1 to 1
% Outputs: Vignetting effect added image (var: vignettImg, Time taken (var: timeTaken)
% Example Usage of Function: [vignettImg, timeTaken]=funcVignettingEffect('Baby1LeftColor.png', 0.5);
% *************************************************************************
function [vignettImg, timeTaken]=funcVignettingEffect(inputImage,scaleLevel)
% Read the input image
try
    % Read an image using imread function
    inputImage=imread(inputImage);
    % grab the number of rows, columns, and channels
    [nr, nc, nChannels]=size(inputImage);
     % Grab the image information (metadata) of input image using the function imfinfo
    inputImageInfo=imfinfo(inputImage);
    % Determine if input left image is already in grayscale or color
    if(getfield(inputImageInfo,'ColorType')=='truecolor')
        colored=1;
    else if(getfield(inputImageInfo,'ColorType')=='grayscale')
        colored=0;
        else
        error('The Color Type of Left Image is not acceptable. Acceptable color types are truecolor or grayscale.');
        end
    end
catch
    % if it is not an image but a variable
    inputImage=inputImage;
    % grab the number of channels
    [nr, nc, nChannels]=size(inputImage);
    if(nChannels)>1
        colored=1;
    else
        colored=0;
    end
end
if scaleLevel <= 0
    error('Scale value must be > 0');
end
vignettImg=inputImage;
tic; % Initialize the timer to calculate the time consumed.
imgCntX = nc/2;
imgCntY = nr/2;
maxDistance = sqrt (imgCntY^2 + imgCntX^2);
if(colored==1)
    for (i=1:nr)
        for (j=1:nc)
           dis = sqrt (abs(i-imgCntY)^2 + abs(j-imgCntX)^2);          
           %% reduce brighness of pixel based on distance from the image center
           vignettImg(i,j,1) = vignettImg(i,j,1)* (1 - (1-scaleLevel)*(dis/maxDistance) );
           vignettImg(i,j,2) = vignettImg(i,j,2)* (1 - (1-scaleLevel)*(dis/maxDistance) );
           vignettImg(i,j,3) = vignettImg(i,j,3)* (1 - (1-scaleLevel)*(dis/maxDistance) );
       end
    end
else
%gray
     for (i=1:nr)
        for (j=1:nc)
           dis = sqrt (abs(i-imgCntY)^2 + abs(j-imgCntX)^2);          
           %% reduce brighness of pixel based on distance from the image center
           vignettImg(i,j) = vignettImg(i,j)* (1 - (1-scaleLevel)*(dis/maxDistance) );
       end
    end
end
% Stop the timer to calculate the time consumed.
timeTaken=toc;