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Fix tutorial code link in basic_linear_transform tutorial. Add some resource links.

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catree 2017-01-17 17:47:27 +01:00
parent 1989d94ef5
commit 00d2e279d7
1 changed files with 10 additions and 3 deletions
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doc/tutorials/core/basic_linear_transform/basic_linear_transform.markdown
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@ -164,13 +164,13 @@ The following image has been corrected with: \f$ \alpha = 1.3 \f$ and \f$ \beta
![By Visem (Own work) [CC BY-SA 3.0], via Wikimedia Commons](images/Basic_Linear_Transform_Tutorial_linear_transform_correction.jpg) ![By Visem (Own work) [CC BY-SA 3.0], via Wikimedia Commons](images/Basic_Linear_Transform_Tutorial_linear_transform_correction.jpg)
The overall brightness has been improved but you can notice that the clouds are now greatly saturated due to the numerical saturation The overall brightness has been improved but you can notice that the clouds are now greatly saturated due to the numerical saturation
of the implementation used. A custom method that preserves the original color range can of course be implemented instead. of the implementation used ([highlight clipping](https://en.wikipedia.org/wiki/Clipping_(photography)) in photography).
The following image has been corrected with: \f$ \gamma = 0.4 \f$. The following image has been corrected with: \f$ \gamma = 0.4 \f$.
![By Visem (Own work) [CC BY-SA 3.0], via Wikimedia Commons](images/Basic_Linear_Transform_Tutorial_gamma_correction.jpg) ![By Visem (Own work) [CC BY-SA 3.0], via Wikimedia Commons](images/Basic_Linear_Transform_Tutorial_gamma_correction.jpg)
The gamma correction should tend to add less saturation effect but should introduce some other type of color artifacts instead. The gamma correction should tend to add less saturation effect as the mapping is non linear and there is no numerical saturation possible as in the previous method.
![Left: histogram after alpha, beta correction ; Center: histogram of the original image ; Right: histogram after the gamma correction](images/Basic_Linear_Transform_Tutorial_histogram_compare.png) ![Left: histogram after alpha, beta correction ; Center: histogram of the original image ; Right: histogram after the gamma correction](images/Basic_Linear_Transform_Tutorial_histogram_compare.png)
@ -185,8 +185,15 @@ and are not intended to be used as a replacement of a raster graphics editor!**
### Code ### Code
Code for the tutorial is [here](changing_contrast_brightness_image.cpp). Code for the gamma correction: Code for the tutorial is [here](https://github.com/opencv/opencv/blob/master/samples/cpp/tutorial_code/ImgProc/changing_contrast_brightness_image/changing_contrast_brightness_image.cpp).
Code for the gamma correction:
@snippet changing_contrast_brightness_image.cpp changing-contrast-brightness-gamma-correction @snippet changing_contrast_brightness_image.cpp changing-contrast-brightness-gamma-correction
A look-up table is used to improve the performance of the computation as only 256 values needs to be calculated once. A look-up table is used to improve the performance of the computation as only 256 values needs to be calculated once.
### Additional resources
- [Gamma correction in graphics rendering](https://learnopengl.com/#!Advanced-Lighting/Gamma-Correction)
- [Gamma correction and images displayed on CRT monitors](http://www.graphics.cornell.edu/~westin/gamma/gamma.html)
- [Digital exposure techniques](http://www.cambridgeincolour.com/tutorials/digital-exposure-techniques.htm)