tft display Gamma correction
Since the eye is not sensitive to changes in light colors, but can easily detect changes in dark colors, this means that pictures designed with linear brightness changes will look strange. What conforms to the characteristics of the human eye is the Gamma 2.2 curve.
What is the Gamma curve?
We know that tft display is divided into 256 gray levels. Different gray levels correspond to different brightness. Gamma2.2 is the curve corresponding to the liquid crystal driving voltage and brightness. Of course, there are also Gamma1.8, Gamma2.4, and Gamma2.6 curves. The difference is that the Gamma1.8 curve corresponds to a higher brightness, the picture looks brighter, and the contrast is lower. And Gamma2.4 or Gamma2.6 The curve looks darker.
We can use photoshop software to simulate images under different curves, so that you can understand the meaning of Gamma more intuitively.
Image of gamma 1.6 curve
Image of gamma 2.2 curve
Image of gamma 2.4 curve
How to correct the Gamma of tft display?
Gamma correction requires professional equipment and methods, testing the brightness of at least 64 gray levels, and then calculating and comparing it with the standard gamma2.2 curve.
Light up the tft display, use Konica Minolta’s CA series optical tester, such as CA-310, CA-410 or other equipment to measure, and then adjust the driver code to make adjustments. The process of debugging the Gamma curve takes a certain amount of time because the test data is large and requires repeated adjustments.
Different display effects can be achieved through different gamma curves to achieve different functions. For example, the eye protection function of some monitors is implemented using different gamma curves. There are also different display modes that can be achieved through gamma curves.
Data for testing different grayscale brightness using CA310
| Test machine：CA310 | Gamma= | 2.1 | 2.3 | 2.2 |
| Gray Level | Gamma=2.1 | Gamma=2.3 | Gamma=2.2 | |
| 1 | 0 | 0.00 | 0.00 | 0.00 |
| 2 | 1 | 0.02 | 0.01 | 0.01 |
| 3 | 2 | 0.07 | 0.03 | 0.05 |
| 4 | 3 | 0.16 | 0.09 | 0.12 |
| 5 | 4 | 0.29 | 0.17 | 0.22 |
| 6 | 5 | 0.46 | 0.28 | 0.36 |
| 7 | 6 | 0.67 | 0.42 | 0.53 |
| 8 | 7 | 0.93 | 0.60 | 0.75 |
| 9 | 8 | 1.23 | 0.82 | 1.00 |
| 10 | 9 | 1.58 | 1.07 | 1.30 |
| 11 | 10 | 1.97 | 1.36 | 1.64 |
| 12 | 11 | 2.41 | 1.70 | 2.02 |
| 13 | 12 | 2.89 | 2.07 | 2.45 |
| 14 | 13 | 3.42 | 2.49 | 2.92 |
| 15 | 14 | 3.99 | 2.96 | 3.44 |
| 16 | 15 | 4.62 | 3.46 | 4.00 |
| 17 | 16 | 5.29 | 4.02 | 4.61 |
| 18 | 17 | 6.00 | 4.62 | 5.27 |
| 19 | 18 | 6.77 | 5.27 | 5.97 |
| 20 | 19 | 7.58 | 5.97 | 6.73 |
| 21 | 20 | 8.45 | 6.71 | 7.53 |
| 22 | 21 | 9.36 | 7.51 | 8.38 |
| 23 | 22 | 10.32 | 8.36 | 9.29 |
| 24 | 23 | 11.33 | 9.26 | 10.24 |
| 25 | 24 | 12.39 | 10.21 | 11.25 |
| 26 | 25 | 13.50 | 11.22 | 12.30 |
| 27 | 26 | 14.65 | 12.28 | 13.41 |
| 28 | 27 | 15.86 | 13.39 | 14.57 |
| 29 | 28 | 17.12 | 14.56 | 15.79 |
| 30 | 29 | 18.43 | 15.78 | 17.06 |
| 31 | 30 | 19.79 | 17.06 | 18.38 |
| 32 | 31 | 21.20 | 18.40 | 19.75 |
| 33 | 32 | 22.66 | 19.79 | 21.18 |
| 34 | 33 | 24.18 | 21.24 | 22.66 |
| 35 | 34 | 25.74 | 22.75 | 24.20 |
| 36 | 35 | 27.36 | 24.32 | 25.79 |
| 37 | 36 | 29.02 | 25.95 | 27.44 |
| 38 | 37 | 30.74 | 27.64 | 29.15 |
| 39 | 38 | 32.51 | 29.39 | 30.91 |
| 40 | 39 | 34.34 | 31.20 | 32.73 |
| 41 | 40 | 36.21 | 33.07 | 34.60 |
| 42 | 41 | 38.14 | 35.00 | 36.53 |
| 43 | 42 | 40.12 | 36.99 | 38.52 |
| 44 | 43 | 42.15 | 39.05 | 40.57 |
| 45 | 44 | 44.23 | 41.17 | 42.68 |
| 46 | 45 | 46.37 | 43.35 | 44.84 |
| 47 | 46 | 48.56 | 45.60 | 47.06 |
| 48 | 47 | 50.81 | 47.91 | 49.34 |
| 49 | 48 | 53.10 | 50.29 | 51.68 |
| 50 | 49 | 55.45 | 52.73 | 54.08 |
| 51 | 50 | 57.86 | 55.24 | 56.53 |
| 52 | 51 | 60.31 | 57.82 | 59.05 |
| 53 | 52 | 62.82 | 60.46 | 61.63 |
| 54 | 53 | 65.39 | 63.17 | 64.27 |
| 55 | 54 | 68.00 | 65.94 | 66.96 |
| 56 | 55 | 70.68 | 68.78 | 69.72 |
| 57 | 56 | 73.40 | 71.69 | 72.54 |
| 58 | 57 | 76.18 | 74.67 | 75.42 |
| 59 | 58 | 79.02 | 77.72 | 78.36 |
| 60 | 59 | 81.90 | 80.84 | 81.37 |
| 61 | 60 | 84.85 | 84.02 | 84.43 |
| 62 | 61 | 87.84 | 87.28 | 87.56 |
| 63 | 62 | 90.89 | 90.60 | 90.75 |
| 64 | 63 | 94.00 | 94.00 | 94.00 |
Gamma curve produced using test data
Should I worry about display gamma correction in my project?
If you have no special requirements, the commonly used curve in the industry is the gamma2.2 curve, which will be set in the initialization code of the tft display provided by the supplier. Usually due to individual differences in the driver IC and LCD panel, the tolerance of the gamma curve is ±0.2 , that is, gamma2.2±0.2, which meets the requirements in most cases. If you need a more stringent display, we also support gamma measurement and setting for each tft display to ensure that the problem of image perception is completely solved. In addition, we support the customization of gamma curves. Whether you need gamma2.2 or an abnormal gamma curve, you can get a perfect approximation solution.
