a propos des isos (question)

[TransFXB]

qu'en pensez-vous ?

Au premier abord, c'est surprenant.
Maintenant, on peut peut être y voir un artefact dû au fait que le bruit ayant monté, il y a plus de grain et donc artificiellement plus de "matière". ce qui donne cette impression de "netteté", un peu à la manière de l'argentique 400 ou 800 ISO....
:34:

D'ailleurs, le site Luminous Landsacpe semble corroborer cet effet :

"Film grain — sometimes grain makes images look sharper — sometimes the opposite!"

"Our perception of sharpness depends to a large extent on how much detail an image contains. Frequently an image with moderately coarse but sharp grain (or crisp digital noise) can appear as sharp or even sharper than a fine-grained image. This is why high-acutance film developers such as Rodinal have historically been preferred by some. They made grain somewhat bigger, but gave it higher acutance and therefore aided in creating the appearance of a sharper image.

Conversely an image with fine but soft grain (for whatever reason) will drag down the general appearance of sharpness that a given image might otherwise have.

Interestingly, completely grain-free images can appear to be less sharp than the resolution numbers might lead one to believe. This is the case with the old Panatomic-X and Tech-Pan films. They are so grain-free than they can appear less than critically sharp if the image doesn't contain a lot of fine detail.

Along the same lines, in the digital realm it's my experience that the Canon D30 at 100 ISO is so free of digital noise (the equivalent of grain) that in some images it can almost appear to be less sharp than a 400 ISO frame from the same camera."

Le lien en entier : http://www.luminous-landscape.com/tu...harpness.shtml