In "normal images" (e.g. photography) illumination is the key factor for good image quality.

The same applies to X-Ray images! (the light and "color" from the X-Ray source)

And of course you need a good camera!
And here is the next similarity: Compared to the big pixel (5µm) from Full Frame Cameras (with 24mmx36mm sensors) the compact cameras with the 1/2.3" sensors and 1.5µm pixel get much less light and sometimes even at daylight the flash is switched on - very funny at locations as in the picture above :mrgreen:. The area of the pixel is less than 1/10th of the full frame sensor resulting in noisy and low contrast images.

The context of the image quality parameter are explained in detail in the paper
.
Coming from the EPS values which is defined in ASTM E1025 and tested with E746 it leads to a formula for the visibility of details in dependence of the spatial resolution (SRb), the Contrast to Noise Ratio (CNR) and the perception threshold of the operator's eye (PT).
PT = dvisible * CNR
with dvisible is the visibility of a smallest just visible detail in the image.

with µeff as effective attenuation coefficient and "Delta w" as difference in wall thickness.
Hint: PT* is different from PT; it depends also slightly on the operator and the viewing conditions.

The main messages of the formula in a nutshell:
(a) With higher spatial resolution in the image smaller details are visible.
(b) With higher CNR (more contrast or less noise) smaller details are visible.
(c) Insufficient spatial resolution can be compensated by higher CNR. This leads to the .