is 24mp enough?

Started Sep 11, 2009 | Discussions thread
em_dee_aitch
Veteran MemberPosts: 3,675
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Re: A very basic question...
In reply to rbmphoto, Nov 14, 2011

rbmphoto wrote:

How do you downrez? Have often heard it referred to, but never any specifics. Are there always benefits? What are the negatives?

Thanks!

There is no single way to downrez. This just refers to resizing the image to a lower resolution using any application. It can be done in Photoshop's Camera RAW, for example, by choosing a lower resolution at the bottom of the Camera RAW editing window (a setting that will stick, including through batches, until you change it again). It can also be done in Photoshop itself afterwards. Theoretically there is always some benefit to this if you are downrezzing by a significant percentage (enough to really help) and do it in the best possible way. What is the best possible way is just a matter of personal experimentation since there is not really a singular agreed upon best method. The whole reason it helps is that by capturing more edge detail (up to a certain limit; too many step beyond the diffraction limit and there is certainly a diminishing return) the photo software has higher continuity of information in crunching those edge numbers, so (when done properly, and at low ISO where noise is not a factor) a D3x image downrezzed to 12.1 MP will look sharper than a D3s image taken natively.

As to negatives, I can think of three (there might be more).

1. If you downrezzed by a less significant margin, say 15 MP to 12 MP, you might hurt more than help. This would require testing to confirm based on the camera in question. I have heard some people say going from 18 to 12 is helpful... I think you want to be at least going 3:2 (in terms of MP, not linear) to definitely see a benefit.

2. If you were doing some form of evidentiary analysis, you could no longer say that you were looking at the "original unmodified" image. I have never done legal photography. Someone who does (for police or trial) would probably have some opinion on image mods in general.

3. If you goof or have not yet mastered your post process... The end result could actually be worse following one of several mistakes I can think of: if you use a cheap editing app that isn't good, if you choose a suboptimal interpolation priority for the downrez, if you have bad sharpening settings, or no sharpening. All digital images need at least minimal sharpening, including after a downrez, so it's important to have the right amount, at least "just enough" and not "too much" I realize that's a totally subjective statement.

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David Hill
http://www.sanfranciscoweddingphotographer.com
San Francisco & San Jose, CA | Austin, TX
Wedding Photographer and Apparent Gearhead

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