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.
Pentax K-1 signal to noise ratio charts
JPEG signal to noise ratio analysis: The K-1 produces an impressive set of figures for a 36MP camera, and is only beaten by the lower-resolution Canon 5D Mk III, but even then not at all sensitivity settings.
Raw (converted to TIFF) signal to noise ratio analysis: The K-1 again performs well, indicating that, apart from at the very high sensitivity settings, it produces images that are relatively free of noise.
Sample Pentax K-1 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.
ISO6400: Click here for a full-size version