# disparity

(Not recommended) Disparity map between stereo images

`disparity`

is not recommended. Use `disparityBM`

or `disparitySGM`

instead. For more information, see Version History

## Description

returns the disparity map, `disparityMap`

= disparity(`I1`

,`I2`

)`disparityMap`

, for a pair of stereo
images, `I1`

and `I2`

.

provides additional control for the disparity algorithm by using one or more
`disparityMap`

= disparity(`I1`

,`I2`

,`Name,Value`

)`Name,Value`

pair arguments.

## Examples

### Compute Disparity Map for a Pair of Stereo Images

Load the images and convert them to grayscale.

I1 = imread('scene_left.png'); I2 = imread('scene_right.png');

Show stereo anaglyph. Use red-cyan stereo glasses to view image in 3-D.

```
figure
imshow(stereoAnaglyph(I1,I2));
title('Red-cyan composite view of the stereo images');
```

Compute the disparity map.

disparityRange = [-6 10]; disparityMap = disparity(rgb2gray(I1),rgb2gray(I2),'BlockSize',... 15,'DisparityRange',disparityRange);

Display the disparity map. For better visualization, use the disparity range as the display range for imshow.

```
figure
imshow(disparityMap,disparityRange);
title('Disparity Map');
colormap(gca,jet)
colorbar
```

## Input Arguments

`I1`

— Input image 1

*M*-by-*N* 2-D grayscale image

Input image referenced as `I1`

corresponding to
camera 1, specified in 2-D grayscale. The stereo images,
`I1`

and `I2`

, must be rectified
such that the corresponding points are located on the same rows. You can
perform this rectification with the `rectifyStereoImages`

function.

You can improve the speed of the function by setting the class of
`I1`

and `I2`

to
`uint8`

, and the number of columns to be divisible by
4. Input images `I1`

and `I2`

must
be real, finite, and nonsparse. They must be the same class.

**Data Types: **`uint8`

| `uint16`

| `int16`

| `single`

| `double`

`I2`

— Input image 2

*M*-by-*N* 2-D grayscale image

Input image referenced as `I2`

corresponding to camera
2, specified in 2-D grayscale. The input images must be rectified such that
the corresponding points are located on the same rows. You can improve the
speed of the function by setting the class of `I1`

and
`I2`

to `uint8`

, and the number of
columns to be divisible by 4. Input images `I1`

and
`I2`

must be real, finite, and nonsparse. They must
be the same class.

**Data Types: **`uint8`

| `uint16`

| `int16`

| `single`

| `double`

### Name-Value Arguments

Specify optional pairs of arguments as
`Name1=Value1,...,NameN=ValueN`

, where `Name`

is
the argument name and `Value`

is the corresponding value.
Name-value arguments must appear after other arguments, but the order of the
pairs does not matter.

*
Before R2021a, use commas to separate each name and value, and enclose*
`Name`

*in quotes.*

**Example: **`'Method'`

,`'BlockMatching'`

, specifies
the `'Method'`

property be set to
`'BlockMatching'`

.

`Method`

— Disparity estimation algorithm

`'SemiGlobal'`

(default) | `'BlockMatching'`

Disparity estimation algorithm, specified as the comma-separated pair
consisting of '`Method`

' and either
`'BlockMatching'`

or
`'SemiGlobal'`

. The disparity function implements
the basic Block Matching [1] and the Semi-Global Block Matching [3] algorithms. In the `'BlockMatching'`

method, the
function computes disparity by comparing the sum of absolute differences
(SAD) of each block of pixels in the image. In the
`'SemiGlobal'`

matching method, the function
additionally forces similar disparity on neighboring blocks. This
additional constraint results in a more complete disparity estimate than
in the `'BlockMatching'`

method.

The algorithms perform these steps:

Compute a measure of contrast of the image by using the Sobel filter.

Compute the disparity for each pixel in

`I1`

.Mark elements of the disparity map,

`disparityMap`

, that were not computed reliably. The function uses –`realmax`

(`'single'`

) to mark these elements.

`DisparityRange`

— Range of disparity

[`0 64`

] (default) | two-element vector

Range of disparity, specified as the comma-separated pair consisting
of '`DisparityRange`

' and a two-element vector. The
two-element vector must be in the format
[*MinDisparity*, *MaxDisparity*].
Both elements must be an integer and can be negative.
*MinDisparity* and *MaxDisparity*
must be in the range [-*image width*, *image
width*]. The difference between
*MaxDisparity* and *MinDisparity*
must be divisible by `16`

. `DisparityRange`

must be real, finite, and nonsparse. If
the camera used to take `I1`

was to the right of the
camera used to take `I2`

, then
*MinDisparity* must be negative.

The disparity range depends on the distance between the two cameras
and the distance between the cameras and the object of interest.
Increase the `DisparityRange`

when the cameras are
far apart or the objects are close to the cameras. To determine a
reasonable disparity for your configuration, display the stereo anaglyph
of the input images in the Image Viewer app and use the
Distance tool to measure distances between pairs of corresponding
points. Modify the *MaxDisparity* to correspond to the
measurement.

`BlockSize`

— Square block size

`15`

(default) | odd integer

Square block size, specified as the comma-separated pair consisting of
'`BlockSize`

' and an odd integer in the range
[5,255]. This value sets the width for the square block size. The
function uses the square block of pixels for comparisons between
`I1`

and I2. `BlockSize`

must be real, finite, and
nonsparse.

`ContrastThreshold`

— Contrast threshold range

`0.5`

(default) | scalar value

Contrast threshold range, specified as the comma-separated pair
consisting of '`ContrastThreshold`

' and a scalar
value in the range (0,1]. The contrast threshold defines an acceptable
range of contrast values. Increasing this parameter results in fewer
pixels being marked as unreliable.`ContrastThreshold`

must be real, finite, and
nonsparse.

`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. Increasing this parameter results in the function
marking more pixels unreliable. When the uniqueness value for a pixel is
low, the disparity computed for it is less reliable. Setting the
threshold to `0`

disables uniqueness thresholding.
`UniquenessThreshold`

must be real,
finite, and nonsparse.

The function defines uniqueness as a ratio of the optimal disparity estimation and the less optimal disparity estimation. For example:

Let K be the best estimated disparity,
and let V be the corresponding SAD (Sum of
Absolute Difference) value. |

Consider V as the smallest SAD value over
the whole disparity range, and v as the
smallest SAD value over the whole disparity range, excluding
K, K-1, and
K+1. |

If v < V *
(`1` +`0.01` *`UniquenessThreshold` ), then the
function marks the disparity for the pixel as
unreliable. |

`DistanceThreshold`

— Maximum distance for left-to-right image checking

`[]`

(disabled) (default) | non-negative integer

Maximum distance for left-to-right image checking between two points,
specified as the comma-separated pair consisting of
'`DistanceThreshold`

' and a nonnegative integer.
Increasing this parameter results in fewer pixels being marked as
unreliable. Conversely, when you decrease the value of the distance
threshold, you increase the reliability of the disparity map. You can
set this parameter to an empty matrix `[]`

to disable
it. `DistanceThreshold`

must be real,
finite, and nonsparse.

The distance threshold specifies the maximum distance between a point
in `I1`

and the same point found from
`I2`

. The function finds the distance and marks
the pixel in the following way:

Let p_{1} be a point
in image I_{1}. |

Step 1: The function searches for point
p_{1}’s best match in
image I_{2}
(left-to-right check) and finds point
p_{2}. |

Step 2: The function searches for
p_{2}’s best match in
image I_{1}
(right-to-left check) and finds point
p_{3}. |

If the search returns a distance between
p_{1} and
p_{3} greater than
`DistanceThreshold` , the
function marks the disparity for the point
p_{1} as
unreliable. |

`TextureThreshold`

— Minimum texture threshold

`0.0002`

(default) | scalar value

Minimum texture threshold, specified as the comma-separated pair
consisting of '`TextureThreshold`

' and a scalar value
in the range [0, 1). The texture threshold defines the minimum texture
value for a pixel to be reliable. The lower the texture for a block of
pixels, the less reliable the computed disparity is for the pixels.
Increasing this parameter results in more pixels being marked as
unreliable. You can set this parameter to `0`

to
disable it. This parameter applies only when you set
`Method`

to
`'BlockMatching'`

.

The texture of a pixel is defined as the sum of the saturated contrast
computed over the `BlockSize`

-by-`BlockSize`

window around the pixel. The function considers the disparity computed
for the pixel unreliable and marks it, when the texture falls below the
value defined by:

*Texture* < *X**
`TextureThreshold`

*
`BlockSize`

^{2}

*X*represents the maximum value supported by the class of the input images,

`I1`

and
`I2`

.
`TextureThreshold`

must be real,
finite, and nonsparse.

## Output Arguments

`disparityMap`

— Disparity map

*M*-by-*N* 2-D grayscale image

Disparity map for a pair of stereo images, returned as an
*M*-by-*N* 2-D grayscale image. The
function returns the disparity map with the same size as the input images,
`I1`

and `I2`

. Each element of the
output specifies the disparity for the corresponding pixel in the image
references as `I1`

. The returned disparity values are
rounded to $$\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$16$}\right.$$th pixel.

The function computes the disparity map in three steps:

Compute a measure of contrast of the image by using the Sobel filter.

Compute the disparity for each of the pixels by using block matching and the sum of absolute differences (SAD).

Optionally, mark the pixels which contain unreliable disparity values. The function sets the pixel to the value returned by -

`realmax`

('`single`

').

## Tips

If your resulting disparity map looks noisy, try modifying the
`DisparityRange`

. The disparity range depends on the distance
between the two cameras and the distance between the cameras and the object of interest.
Increase the `DisparityRange`

when the cameras are far apart or the
objects are close to the cameras. To determine a reasonable disparity for your
configuration, display the stereo anaglyph of the input images in the Image Viewer app and use the Distance tool to measure distances between pairs
of corresponding points. Modify the *MaxDisparity* to correspond to the
measurement.

## References

[1] Konolige, K., *Small Vision Systems: Hardware and
Implementation*, Proceedings of the 8th International Symposium in
Robotic Research, pages 203-212, 1997.

[2] Bradski, G. and A. Kaehler, *Learning OpenCV :
Computer Vision with the OpenCV Library*, O'Reilly, Sebastopol, CA,
2008.

[3] Hirschmuller, H., *Accurate and Efficient Stereo
Processing by Semi-Global Matching and Mutual Information*, International
Conference on Computer Vision and Pattern Recognition, 2005.

## Extended Capabilities

### C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

`'Method'`

must be a compile-time constant.Generates portable C code using a C++ compiler that links to OpenCV (Version 3.4.0) libraries. See Portable C Code Generation for Functions That Use OpenCV Library.

## Version History

**Introduced in R2011b**

### R2019a: `disparity`

function will be removed

The `disparity`

function will be removed in a future release.
Use `disparityBM`

or `disparitySGM`

instead. Use `disparityBM`

to compute disparity map using block matching method.
Use `disparitySGM`

to compute disparity map using semi-global matching
method.

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