HaomiaoJiang

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Background

Display Characterization

Figure 1 SPD Shape under Different Brightness Levels

Display characterization is the process to build proper models for certain displays and estimate the underlying parameters. The display characteristics are usually measured in two categories, spatial properties and temporal properties. Spatial properties mainly include display gamma value, color bit depth, spectral power distribution, color spectral additivity, pixel independence and so on. Temporal properties include refresh rate, color breakup and so on. Among them, color bit-depth, refresh rate are given by the manufacture and these parameters will not vary a lot between displays. Also, shape of spectral power density is similar among LCD displays, which is shown in figure 1 on the right.

However, gamma values are different from display to display, even if they are from the same manufacture. So measuring or estimating the gamma for each display is essential in calibrating the display model.

Gamma Curve

Gamma curve characterize the relationship between the inputs value and the output luminance levels. Actually, this encodes and decodes luminance or tristimulus values in video or still image systems.

Gamma is also sometimes called gamma correction, gamma nonlinearity or gamma encoding. Mathematically, gamma correction is, in the simplest cases, defined by the power-law expression:

$V_{out}=AV_{in}^{\gamma }$

Since black is not purely black and there always more or less exists ambient lighting, we can add a constant term as

$V_{out}=AV_{in}^{\gamma }+c$

Usage in Vision Experiment

Measuring gamma value of display is essential in preparation of most of the vision experiments. With gamma value and SPD of the display, we can estimate the spectrum of light coming into the subjects eye. Then, we can transform the spectrum to XYZ or even other color space to do further processing. This process can be described by formular below

 $XYZ=ieXYZfromEngery(SPD*(AV_{in}^{\gamma }+c_{1})+c_{2}))$

Here $c_{1}$ stands for the luminance of black and $c_{2}$ stands for the ambient lighting spectrum.

Measuring Methods

Traditional Measuring Methods

Retinotopic maps were obtained in 5 subjects using Population Receptive Field mapping methods Dumoulin and Wandell (2008). These data were collected for another research project in the Wandell lab. We re-analyzed the data for this project, as described below.

Dithering Methods

Subjects were 5 healthy volunteers.

Online Dithering Test

Data were obtained on a GE scanner. Et cetera.

Test Results

Subjects and Test Environment

Some text. Some analysis. Some figures.

Dithering Method Test Results

Some text. Some analysis. Some figures.

Online Dithering Test Results

Some text. Some analysis. Some figures. Maybe some equations.

Conclusions

Here is where you say what your results mean.

References - Resources and related work

References

Software

Appendix I - Code and Data

Code

File:CodeFile.zip

Data

zip file with my data