Dissecting equivalence

Started Sep 15, 2014 | Discussions thread
Great Bustard Forum Pro • Posts: 43,440
Required reading.
2

dtmateojr wrote:

From a previous thread, this thought experiment was proposed:

==========

Supposing I have a m43 camera and I take a shot with a 25mm lens.

Now I take 4 more shots of the same scene but this time I intentionally underexpose by 2 stops and use a 50mm lens so that I can neatly stitch all 4 frames edge to edge to come up with the same AoV as the first shot.

If I print the resulting two images at 12x16 which one will have better SNR?

==========

The noise in the stitched photo will be greater at a higher frequency. If viewed from a distance that this higher frequency noise cannot be perceived, the noise will be the same except for the portions of the photo made with very little light. The reason is that the stitched photo will have more read noise per proportion of the photo (precisely double if the photos were taken at the same ISO setting or an ISOless region of the sensor performance), and read noise becomes significant in very low light.

After 4 hours, two brave souls concluded that both images will result in the same SNR at any arbitrary print size while another forumite thinks it is strange.

Let's wait for others because I have a feeling that the supposed "experts" in equivalence are scared of the implications and would rather not step forward with their analysis.

If noise filtering is applied to the stitched photo, then it will have less noise and remain more detailed, as demonstrated with this example (courtesy of Lee Jay):

We will discuss the implications because this thought experiment is the heart of equivalence-fu.

Any other takers?

Required reading:

http://www.dpreview.com/forums/post/54385829

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