Gamma Correction

Apply or remove gamma correction to or from image or video stream

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Libraries:
Computer Vision Toolbox / Conversions

Description

The Gamma Correction block applies or removes gamma correction to or from an image or video stream.

Examples

Perform Gamma Correction of Image

Perform gamma correction of an image.

Open Script

Ports

Input

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I — Input image
matrix | array

Input image, specified as an M-by-N matrix or an M-by-N-by-C array, where C is the number of color channels in the input image.

Dependencies

To enable this port, set the Operation parameter to Gamma.

I' — Gamma-corrected input image
matrix | array

Gamma-corrected input image, specified as an M-by-N matrix or an M-by-N-by-C array, where C is the number of color channels in the input image.

Dependencies

To enable this port, set the Operation parameter to De-gamma.

Output

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I' — Gamma-corrected output image
matrix | array

Gamma-corrected output image, returned as an M-by-N matrix or an M-by-N-by-C array, where C is the number of color channels.

Dependencies

To enable this port, set the Operation parameter to Gamma.

I — Gamma-removed output image
matrix | array

Gamma-removed output image, returned as an M-by-N matrix or an M-by-N-by-C array, where C is the number of color channels.

Dependencies

To enable this port, set the Operation parameter to De-gamma.

Parameters

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Operation — Block operation
`Gamma` (default) | `De-gamma`

Specify the gamma operation the block performs.

Gamma — Apply gamma correction to the input image.
De-gamma — Remove gamma correction from the input image.

Gamma — Gamma value
`2.2` (default) | scalar

Specify the gamma as a value greater than or equal to 1. A value less than 1 encodes luminance values in image and a value greater than 1 decodes luminance values in image, represented as gamma compression and gamma expansion respectively.

Linear segment — Linear segment
`on` (default) | `off`

Select this parameter to define the gamma curve as a linear segment near the origin. For more information, see Gamma Correction Method.

Break point — Break point value
`0.018` (default) | scalar

Specify a scalar break point value, which indicates the I-axis value at the end of the gamma curve linear segment. For more information, see Gamma Correction Method.

Dependencies

To enable this parameter, select the Linear segment parameter.

Block Characteristics

Data Types	`double` \| `fixed point^a` \| `integer^a` \| `single`
Multidimensional Signals	`yes`
Variable-Size Signals	`yes`
^a Supports word lengths less than or equal to 16 bits.

Algorithms

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Gamma Correction Method

For input signals normalized between 0 and 1, gamma correction is defined by these equations. For integers and fixed-point data types, these equations are generalized by applying scaling and offset values specific to each data type.

S_LS is the slope of the straight line segment. B_P is the break point of the straight line segment, which corresponds to the Break point parameter. F_S is the slope-matching factor, which matches the slope of the linear segment to the slope of the power function segment. C_O is the segment offset, which ensures that the linear segment and the power function segments connect. This figure shows the slope of the straight line segment S_LS and break point of the straight line segment B_P for gamma and de-gamma operations.

By linearizing the input normalized signal, the block removes gamma correction as defined by this equation.

Typical gamma values range from 1 to 3. Most LCD monitor gamma values range from 1.8 to 2.2. Check with the manufacturer of your hardware to obtain its gamma value. This table shows the gamma function parameters for different standards.

Standard	Slope	Break Point	Gamma
CIE L*	9.033	0.008856	3
Recommendation ITU-R BT.709-3, Parameter Values for the HDTV Standards for Production and International Programme Exchange	4.5	0.018	$\frac{20}{9}$
sRGB	12.92	0.00304	2.4

References

[1] Poynton, Charles A. Digital Video and HDTV: Algorithms and Interfaces. Morgan Kaufmann Series in Computer Graphics and Geometric Modeling. Amsterdam ; Boston: Morgan Kaufmann Publishers, 2003.

Gamma Correction

Description