TFT Gamma Calibrator

WORK IN PROGRESS (ALPHA)

The screenshots below show test patterns from an interactive gamma curve checker web tool. These can be used to compare gamma responses between displays, which is a useful proxy for the more difficult task of comparing color gamuts.

For each of the 7 gray bars in the test pattern, the left half is a checkerboard dither pattern while the right half is a solid color. When your display's gamma response matches the gamma curve defined by the slider values, the gray bars should appear equally bright from left to right. On a display with some other gamma response, the left and right halves won't match.

This curve is for an LED backlit Dell monitor that I attempted to configure for displaying colors as sRGB. The monitor specs say it has a CIE1976 82% gamut, which, as best I can tell, is approximately the full sRGB gamut. The table below shows how I configured macOS and the monitor in my attempt to turn off features that would skew color reproduction away from sRGB.

Device	Setting	Value
mac	Displays > Color profile	sRGB IEC61966-2.1
monitor	Brightness	20%
	Contrast	100%
	Display Settings > Sharpness	50%
	Color Settings > Image Enhance	Off
	Color Settings > Preset Modes	Standard

Curve for 2010's Tablets/Laptops

This curve uses slider values averaged from some mid-2010 good quality LED backlit tablet and laptop displays, configured to use their default color profiles.

Curve for 2020's P3 Wide Gamut

This curve uses slider values averaged from some 2020's devices with P3 wide gamut displays, configured to use their default color profiles.

Test PNG (web style)

This is a cropped and rotated version of the screenshot above, but I removed the embedded ICC profile from the PNG file. PNG files are often prepared this way to match how some popular web browsers render CSS colors.

Test PNG with Embedded Color Profile

This is a cropped and rotated version of the screenshot above, and it includes an embedded sRGB color profile. Some software may not display PNG files as sRGB unless there is an embedded ICC color profile. It might be interesting to see if this image looks the same as the previous image that lacks the embedded color profile.

Hardware

Parts

• Adafruit ESP32-S3 TFT Feather - 4MB Flash, 2MB PSRAM (product page, learn guide)

Pinouts

TFT feather	ST7789 TFT
SCK	SCK
MOSI	MOSI
MISO	MISO
TFT_CS	CS
TFT_DC	DC

Updating CircuitPython

NOTE: To update CircuitPython on the ESP32-S3 TFT Feather with 2MB PSRAM and 4MB Flash, you need to use the .BIN file (combination bootloader and CircuitPython core)

1. Download the CircuitPython 9.1.4 .BIN file from the Feather ESP32-S3 TFT PSRAM page on circuitpython.org

2. Follow the instructions in the Web Serial ESPTool section of the "CircuitPython on ESP32 Quick Start" learn guide to update your board: first erase the flash, then program the .BIN file.

Installing CircuitPython Code

To copy the project bundle files to your CIRCUITPY drive:

1. Download the project bundle .zip file using the button on the Playground guide or the attachment download link on the GitHub repo Releases page.

2. Expand the zip file by opening it, or use unzip in a Terminal. The zip archive should expand to a folder. When you open the folder, it should contain a README.txt file and a CircuitPython 9.x folder.

3. Open the CircuitPython 9.x folder and copy all of its contents to your CIRCUITPY drive.

To learn more about copying libraries to your CIRCUITPY drive, check out the CircuitPython Libraries section of the Welcome to CircuitPython! learn guide.