Transforming image contrast and brightness

In this recipe we will cover basic image color transformations using the Surface class for pixel manipulation.

Getting ready

To change the values of contrast and brightness we will use InterfaceGl covered in Chapter 2, Preparing for Development in the Setting up GUI for parameters tweaking recipe. We will need a sample image to proceed with; save it in your assets folder as image.png.

How to do it...

We will create an application with simple GUI for contrast and brightness manipulation on the sample image. Perform the following steps to do so:

1. Include necessary headers:

   #include "cinder/gl/gl.h"
   #include "cinder/gl/Texture.h"
   #include "cinder/Surface.h"
   #include "cinder/ImageIo.h"

2. Add properties to the main class:

   float mContrast,mContrastOld;
   float mBrightness,mBrightnessOld;
   Surface32f  mImage, mImageOutput;

3. In the setup method an image is loaded for processing and the Surface object is prepared to store processed image:

   mImage = loadImage( loadAsset(...