Transcript Matlab Lecture 2

MATLAB LECTURE 2
Image Enhancement in the Spatial Domain
(MATLAB)
IMAGE ENHANCEMENT IN THE SPATIAL
DOMAIN
SPATIAL DOMAIN: BACKGROUND

g(x, y) = T [f(x, y)]
f(x, y) : input image
 g(x, y) : output image
 T : an operator on f (Transformation Function)

IN MATLAB: FUNCTION IMADJUST
Adjust image intensity values or colormap
 Syntax : (in gray images)
J = imadjust(I)
maps the values in intensity image I to new
values in J. This
increases the contrast of the output image J.
 J = imadjust(I,[low_in high_in],[low_out
high_out])
maps the values in intensity image I to new
values in J such
that values between low_in and high_in map to
values between low_out and high_out.

FUNCTION IMADJUST
J = imadjust(...,gamma)
 maps the values in intensity image I to new
values in J, where gamma specifies the shape of
the curve describing the relationship between the
values in I and J.

FUNCTION IMADJUST (CONT.)

If gamma is less than 1, the mapping is weighted
toward higher (brighter) output values. If gamma
is greater than1, the mapping is weighted toward
lower (darker) output values. If you omit the
argument, gamma defaults to 1(linear mapping).
IMAGE ADJUST EXAMPLES (MATLAB
CODE)

Adjust a low-contrast grayscale image.
I = imread('pout.tif');
J = imadjust(I);
figure, imshow(I), figure, imshow(J)
IMAGE ADJUST EXAMPLES

Adjust the grayscale image,
specifying the contrast limits.
K1 = imadjust(I,[0.3 0.7],[.2 .6]);
figure, imshow(K1)
K2 = imadjust(I,[0.3 0.7],[]);
figure, imshow(K2)
IMAGE ADJUST EXAMPLES
Adjust the gamma
L1 = imadjust(I,[0.3 0.7], [ ],2);
figure, imshow(L1)
L2 = imadjust(I,[0.3 0.7], [ ],.3);
figure, imshow(L2)
NEGATIVE IMAGE
Obtaining a negative image
I = imread('pout.tif');
K1 =imadjust(I, [0 1] , [1 0]);
K2 = imcomplement(I);
imshow(I), figure, imshow(K1), figure,
imshow(K2)
STRETCHLIM
EXAMPLE
Contrast Stretching:
I = imread('pout.tif');
J = imadjust(I,stretchlim(I),[]);
imshow(I), figure, imshow(J)
LOGARITHMIC AND CONTRAST
STRETCHING
Logarithmic:
g=c*log(1+double(f))
 Contrast stretching :
compress the input levels lower than m into a
narrow range of dark levels in the output image;
similarly, it compresses the values above m into a
narrow band of light levels in the output.

LOGARITHMIC AND CONTRAST
STRETCHING EXAMPLE
I = imread('pout.tif');
g=c*log(1+double(I))
gs=im2uint8(mat2gray(g));
THRESHOLDING EXAMPLE
I = imread('pout.tif');
threshold = graythresh(I);
BW = im2bw(I,threshold);
imshow(BW);
IN MATLAB: IM2BW
Convert an image to a binary image, based on
threshold
 Syntax:
BW = im2bw(I,level)
BW = im2bw(X,map,level)
BW = im2bw(RGB,level)

IM2BW: EXAMPLE
Im2bw: Example
load trees
BW = im2bw(X,map,0.4);
Imview(X,map), imview(BW)