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 GX8 signal to noise ratio charts
JPEG signal to noise ratio analysis: These scores are consistent with the GX8's ability to capture a good level of detail while controlling noise well for the majority of the sensitivity range.
Raw (converted to TIFF) signal to noise ratio analysis: This is an especially strong set of results from the GX8, which indicate that raw files don't have a huge level of noise.
Sample Panasonic GX8 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.