image denoising

Can any body tell me which factors influence in selecting threshold value for image denoising

Answer 1

[Sean de Wolski]

Amount of noise.

Answer 2

[Walter Roberson]

Also, what one is looking for in the image. Consider the difference between astronomical images vs reducing flash reflections in portraits. Even within astronomical images, for the very same image, sometimes one wishes to examine the "obvious" features and sometimes one wishes to examine subtle things such as the infrared spectra between the stars.