Using a Phone to Calibrate an 8K TV
Samsung has released new software called Smart Calibration that allows ordinary consumers to calibrate their 4K or 8K TV in their own living room without a professional calibrator. The software offers various levels of calibration fidelity and can even be a time saver for professional calibrators. To better understand the process, we visited Samsung’s QA Lab in New Jersey for a demonstration of the two calibration modes: Basic and Pro.
We learned that the problem Samsung faced with using a phone to calibrate a TV is that a phone’s camera is not a precise light-measuring instrument. Secondly, calibration is done in the XYZ color space while the phone’s camera captures data in the RGB color space. The key to solving this problem was a matrix transformation that converted the phone’s RGB color information into XYZ color coordinates. This matrix was successfully developed but no phone camera is a calibrated sensor. Consequently, calibration results will vary depending on the mode and optional steps to calibrate the phone’s camera.
To start the Smart Calibration process, the user first downloads the SmartThings App to their Samsung Galaxy smartphone or Apple iPhone. So far, only 2022 Neo QLED TVs (and Samsung Freestyle projectors) have the firmware to support Smart Calibration. The user opens the App and connects to the TV over Wi-Fi.
In the Basic mode, the TV will display the pattern shown below. Place the rear camera of smartphone 1-3cm from the white rectangle area on the TV and select start. A simple 2-point calibration of the white point can be done this way in 15-30 seconds. These settings are stored in the TV.
Note: Calibration is done using SDR patterns and luminance levels, but should work well for HDR content too. Once the TV is calibrated a (calibrated) note will be added to the movie mode menu listing so the user knows their status (but not which calibration mode, Basic or Pro was used).
In the figures below, we show the measured default factory settings in the screen capture below (top) and the resulting Basic calibration results (bottom). Note the improvement in the DeltaE2000 values from an average of 2.8 to 1.9 along with a more consistent white point as a function of luminance (IRE). DeltaE2000 is a way of assessing the accuracy of the picture quality values. Results of less than 3 are good, but lower is better. White point consistency is desired so that the color temperature of white remains the same regardless of luminace level. The white point correlated color temperature (CCT) should be 6500 (degrees Kelvin). A higher CCT will have a blueish tint and a lower value a redish tint.
For the Pro mode, a more tradition set of patterns is displayed and Samsung recommends the phone be placed on a tripod and the room darkened. A 20-point white point calibration and gamma linearity check is now done by the phone. This procedure takes 5-8 minutes to complete and is designed to produce a more accurate result.
To test this out, we first intentionally skewed the red, green and blue primaries at several luminance values. We took ‘before’ readings, ran the Pro mode calibration, and looked at the results. These are shown below (before top; after bottom). Note that the deltaE2000 readings improved from an average of 4.2 to 1.2 with a nice consistent white point.
To get even better results the phone camera needs to be calibrated. This requires a colorimeter like the CA410. Using the color meter, the full screen white, gray, red, green and blue screens are presented and the luminance and CIE color coordinates measured. The smartphone then does the same measurements providing details on how the phone’s camera is different from the color meter. Using this data, the calibration of the TV was further adjusted to improve the deltaE2000 to an average of 0.7 with even better white point consistency and gamma accuracy.
Clearly not all consumers will have a color meter so actual calibration of the phone’s camera will not be very practical. But for consumers who have one and/or professional calibrators, calibrating the phone and using it can save time and equipment. For example, normally calibration requires a pattern generator and PC along with the color meter to perform the calibration. But if the phone is now calibrated, there is no need for the pattern generator or PC – and the adjustments happen automatically, not manually.
The development of Smart Calibration is an important step to ensuring that accurate images can be presented to the user as the content creator intended.