raw data

1. posterization

    any 'histgram stretch' may produce posterization because the limited levels has to fill a broader range than origin. Some empty bins will be created. mostly the posterization happens in gradual color region, sky e.g.

2. exposure compensation

      even after captured, the exposure of raw data (before gamma correction) can be  

      adjusted slightly! but how?

3. something about exposure in camera

      each camera has a default 'middle gray' ( it has a definition in printing document but the 

      producers just ignore it). the EC in-camera tries to control some parameters to adjust

      the light of object to 'middle gray'. Then if the camera is focused on a the most light 

      region in one scene, it produces a underexposure photo. Otherwise if the camera is 

      focused on the most dark region in one scene, it produce a overexposure photo. it is 

      best to make it focus on a region which stands for the scene illumination. finally which

    region to focus on is an option in camera called metering option.

    one tip: all camera now only meter the reflecting light but the incident light( incident light

    is light directly from one light source, sun, light. for example)

4.the flowchart

    a) transform bayer matrix to three-channel matrix without changing depth

        raw data interpolation

        A demosaicing algorithm is a digital image process used to reconstruct a full color

      image from the incomplete color samples output from an image sensor overlaid with 

      a color filter array (CFA). Also known as CFA interpolation or color reconstruction,

      another common spelling is demosaicking.

    b) white balance (no depth change)

        convert three-channel matrix to RGB matrix by definite what is white color

    c) color model convert

        if necessary, you can convert pixel matrix from RGB to other color space, .e.g YCbCr

    d) gamma correction

        adjust contrast according to human vision

    e) remove disturbed color,   sharp the edge, noise removal,

    f)   color depth change

        convert the depth into lower one for display.