Compute disparity map through semi-global matching
Load a rectified stereo pair image.
I1 = imread('rectified_left.png'); I2 = imread('rectified_right.png');
Create the stereo anaglyph of the rectified stereo pair image and display it. You can view the image in 3-D by using red-cyan stereo glasses.
A = stereoAnaglyph(I1,I2); figure imshow(A) title('Red-Cyan composite view of the rectified stereo pair image')
Convert the rectified input color images to grayscale images.
J1 = rgb2gray(I1); J2 = rgb2gray(I2);
Compute the disparity map through semi-global matching. Specify the range of disparity as [0, 48], and the minimum value of uniqueness as 20.
disparityRange = [0 48]; disparityMap = disparitySGM(J1,J2,'DisparityRange',disparityRange,'UniquenessThreshold',20);
Display the disparity map. Set the display range to the same value as the disparity range.
figure imshow(disparityMap,disparityRange) title('Disparity Map') colormap jet colorbar
I1— Input image 1
Input image referenced as
I1 corresponding to camera 1,
specified as a 2-D grayscale image or a
gpuArray object. The function uses this image as the reference image for
computing the disparity map. The input images
I2 must be real, finite, and nonsparse. Also,
I2 must be of the same size and same
I2— Input image 2
comma-separated pairs of
the argument name and
Value is the corresponding value.
Name must appear inside quotes. You can specify several name and value
pair arguments in any order as
'DisparityRange'— Range of disparity
[0 128](default) | two-element vector
Range of disparity, specified as the comma-separated pair consisting of
'DisparityRange' and a two-element vector of the form
MaxDisparity]. MinDisparity is the minimum
disparity and MaxDisparity is the maximum disparity.
For input images of width N, the MinDisparity and MaxDisparity must be integers in the range (–N, N). The difference between the MaxDisparity and MinDisparity values must be divisible by 8 and must be less than or equal to 128.
The default value for the range of disparity is
[0 128]. For
more information on choosing the range of disparity, see Choosing Range of Disparity.
'UniquenessThreshold'— Minimum value of uniqueness
15(default) | non-negative integer
Minimum value of uniqueness, specified as the comma-separated pair consisting of
'UniquenessThreshold' and a nonnegative integer.
The function marks the estimated disparity value K for a pixel as unreliable, if:
v < V×(1+0.01×
where V is the Hamming distance corresponding to the disparity value K. v is the smallest Hamming distance value over the whole disparity range, excluding K, K–1, and K+1.
Increasing the value of
results in disparity values for more pixels being marked as unreliable. To disable the
use of uniqueness threshold, set this value to 0.
disparityMap— Disparity map
Disparity map for rectified stereo pair image, returned as a 2-D grayscale image or
gpuArray object. The function returns the disparity map with the
same size as input images
value in this output refers to the displacement between conjugate pixels in the stereo
pair image. For details about computing the disparity map, see Computing Disparity Map Using Semi-Global Matching.
The input images
must be rectified before computing the disparity map. The rectification ensures that the
corresponding points in the stereo pair image are on the same rows. You can rectify the
input stereo pair image by using the
rectifyStereoImages function. The reference image must be the same for
rectification and disparity map computation.
The range of disparity must be chosen to cover the minimum and the maximum amount of
horizontal shift between the corresponding pixels in the rectified stereo pair image. You
can determine the approximate horizontal shift values from the stereo anaglyph of the stereo
pair image. Compute the stereo anaglyph of the rectified images by using the
stereoAnaglyph function. Display the stereo anaglyph in the Image Viewer by
imtool function. To measure the amount of
horizontal shift between the corresponding points in the stereo pair image, select Measure Distance from the Tools
menu in Image Viewer. Choose the minimum and maximum disparity values for the range of
disparity based on this measurement.
For example, this figure displays the stereo anaglyph of a rectified stereo pair image and the horizontal shift values measured between the corresponding points in the stereo pair image. The minimum and maximum shift values are computed as 8 and 31 respectively. Based on these values, the range of disparity can be chosen as [0, 48].
Compute Census transform of the rectified stereo pair image.
Compute Hamming distance between pixels in the census-transformed image to obtain the matching cost matrix.
Compute the pixel-wise disparity from matching cost matrix by using the semi-global matching method given in .
Optionally, mark the pixels for unreliability based on the
UniquenessThreshold name-value pair. The function sets the
disparity values of the unreliable pixels to
 Hirschmuller, H. "Accurate and Efficient Stereo Processing by Semi-Global Matching and Mutual Information." In Proceedings of the IEEE Conference on Computer Vision and Pattern Recognition (CVPR), pp. 807-814. San Diego, CA: IEEE, 2005.
Usage notes and limitations:
The GPU version of this function works only on NVIDIA GPUs.