These are the settings we used to calibrate the 55" TCL P607 (55P607). These setting are good for most content, from TV shows to movies and gaming. For gaming, some changes are needed to have the best input lag, and they are listed below.
We used the 'Movie' picture mode to get as close as possible to our calibration goal. The 'TV brightness' was set to 'Darker' for our totally dark room, but you can set it to a brighter setting if you have a room with more light. The 'Picture Size' was left to 'Auto' since under this setting, the TV will adjust the picture size to match the screen size by itself.
In the 'Advanced picture settings', we set the 'Local contrast' off for the calibration process, but for regular use, you should set it to 'High' ('Local contrast' is TCL's local dimming option). If you find that the screen luminance changes too much by itself depending what is displayed on the screen, you can set it to be less strong or simply turn it off. The 'Backlight' was set to 0 for our completely dark room, but here again, you should set it to match your room lighting. Note that here the 'backlight' works in combination with the 'TV brightness' option, giving you a more granular control of the TV luminance. 'Brightness' was left to 50 and the 'Contrast' to 100. The 'Sharpness' was set to 0 so that no oversharpness is added to the original content. 'Color' was left to 45 and 'Tint' to 0, their default values. The 'Color temperature was set to 'Warm' since it is the color temperature the closest to our calibration goal, but you can set it to a colder temperature if you find the screen to be too yellow or red.
If you intend to watch HDR content via an HDR UHD Blu-ray player or via an HDR video game console connected via HDMI, you will have to set the 'HDMI mode' to 'HDMI 2.0' for the HDMI port. This option is situated in the 'TV inputs' menu. For HDR content, the TV will change picture mode to match the type of HDR content (Dolby Vision or HDR10) by itself, but if you want to be sure you have the best setting, just verify that the 'TV brightness' is set to the brighter setting (from the 'Options' menu), that the 'Backlight' is set to maximum and 'Local contrast' is set to 'High' (both from the 'Advanced picture settings').
Update 01/26/2018: There is a bug with the 'Color' slider in HDR: sometimes when the slider is increased then decreased immediately, or vice versa, the TV freezes, crashes and reboots. This shouldn't be a problem for normal usage though.
For playing video games in SDR or HDR, via video game console or PC, simply turn on 'Game mode' from the 'Advanced picture settings to have the best input lag possible.
Note: When in game mode, the local dimming feature (named 'Local contrast') is not available. If you want to play video games with local dimming turned on, you will have to turn off the local dimming feature. The input lag outside game mode with a 4k@60Hz resolution is still very reasonable on this TV, as it is of 34.1 ms in SDR and 31.8 ms in HDR.
Expert Picture Settings
There are some settings that are only available via the mobile Roku apps. The Roku app is compatible with iOS and Android devices and can be downloaded via either the Apple App Store or via Google Play store. For more in for on the Roku app itself, you can access this page. To access those setting, you need to go to the 'Setting' tab, and then go to 'Expert Picture Settings'.
In the 'Expert Picture Settings' menu, you can set the 'Picture mode', 'Gamma', 'Noise Reduction', 'Color temperature', the '11 points White balance' calibration and the 'Color Space' calibration. Some settings like the picture mode and color temperature are redundant and don't need to be changed again if already set from the TV settings. For our calibration and to get the best picture quality, set the 'Gamma' to 2.2. If you are watching SDR or HDR content and you find that you are losing too much detail in the dark area of the screen (black crunsh) or the white (clipping) you can change the 'Gamma' value to a lower or higher setting. We also set the 'Noise Reduction to 'Off'. This can be turned on if you are watching some older low-resolution video since it can help to reduce compression artifacts often present on older content. If you intend to do a calibration, then you will need to change the value in the '11 Pt WB' (the white balance control) and change the 'Color Space' setting to 'Custom' and change the value for each color. Note that each color temperature has it separate calibration data, so if you calibrate on the 'Warm' color temperature, your correction won't be applied if you change the color temperature to another one.
The following are the results of the white balance and colorspace calibration on our unit. They are provided for reference, and should not be copied as the calibration values vary per individual unit even for the same model and same size as the TV we reviewed due to manufacturing tolerances. If you want to try them you will need to enter all values shown, as all of them are active at the same time. If you end up with worse picture quality, simply reset them to the default values.