This is a test of the camera's noise levels. The higher the signal to noise ratio, the greater the difference in strength between the real image data and random background noise, so the 'cleaner' the image will look. The higher the signal to noise ratio, the better.
Panasonic GX80 signal to noise ratio charts
JPEG signal to noise ratio analysis: The GX80 is the clear leader here, indicating that its JPEG images have less noise than the competing cameras.
Raw (converted to TIFF) signal to noise ratio analysis: Apart from at the lowest sensitivity settings the GX80's raw files (after conversion to TIFF) don't compare so well to the competition as its JPEGs do. The G7 produces cleaner images for its entire ISO range, and the Olympus E-M10 II does from around ISO800 upwards.
Sample Panasonic GX80 ISO test results
The signal to noise ratio charts use laboratory test equipment, but we also shoot a real-world scene to get a visual indication of the camera's noise levels across the ISO range. The right side of the scene is darkened deliberately because this makes noise more obvious.
ISO 200: Click here for a full-size version
ISO 6400: Click here for a full-size version