gvarner Loc: Central Oregon Coast

If you shoot full frame with 30 MP and crop to 2/3 of that in post, do you get an equivalent 20 MP edited photo?

imagemeister Loc: mid east Florida

That is the normal assumption. But, many people do not realize that you can use software to restore ( pixel enlargement) the original pixel count.

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a6k Loc: Detroit & Sanibel

If you crop to 2/3 area you cropped to the square root of 2/3 linear which is .8165.

Your hypothetical 30 MP is approximately 4800 x 7200 pixels, assuming the usual aspect ration of 1: 1.5.

Your linear crop would be 3919 x 5878 pixels, again assuming the same aspect ratio.

I'm unsure what you mean by "an equivalent 20 MP edited photo".

CHG_CANON Loc: the Windy City

You get whatever the pixel size of the resulting images calculates to. Images coming off a 5DIV are 6720 × 4480 = 30,105,600 pixels = 30.1 effective megapixels (divide by 1-million)

If you want to know the pixel resolution of your cropped image, simply do the math. Did you retain a 3x2 aspect and crop to 2016 x 1344? If you did, that's a 2.7MP image.

Did you change the crop to a 5x4 aspect? Is the image now 5000 x 4000? That would be a 20MP image.

burkphoto Loc: High Point, NC

You may not have intended it as such, but this is REALLY a trick question!

The honest answer is that you get a 20MP image cropped from a 30MP original file. You're not getting the full resolution of the lens and sensor combination.

Of course, at a certain point, you must re-size the image through software interpolation to enlarge it, but at some point, you dip below the required 240 pixels per inch of ORIGINAL, in-camera generated pixels required to spread over each linear inch of output, in order to meet extinction resolution at 12.8 inches from an 8x10 print.

Extinction resolution is the point at which your eyes cannot resolve any more detail from an image, even if you increase the available pixel count. Most labs will tell you that 240 to 250 PPI — un-interpolated, from the original file — is what is needed to preserve all the detail you can see at 8x10. As the print size and appropriate viewing distance increase, that number is reduced. Conversely, at smaller print sizes, it is INCREASED. (Yes, that's counter-intuitive, I know, but true.)

All that said, a 20MP crop from a 30MP original will make a very large print from most subject matter. 30x40 inches is not outside the realm of acceptability, unless your subject matter DEMANDS up-close pixel peeping (such as a large group of people, or a highly detailed landscape, or a military spy photo). I've made a few un-cropped 40x30 prints from 16MP Micro 4/3 images, and they look just fine when you view an entire print from 50".

In general, people put far too much emphasis on MP count. Thousands of the best, most dramatic and iconic images of the 20th century were made with far less effective resolution than can be had from a 30MP camera.

I once worked for a designer whose motto was, "If you can't make it GOOD, make it BIG." I believe the original source of that was a Time-Life magazine editor. They were known for occasional "double-truck bleed" center-fold photos of important events. Many of those were from 35mm Tri-X negatives, carefully push-processed in soft-working developers like Acufine. Our tools are much better today! Go forth and make images while there is still light to do so!

PHRubin Loc: Nashville TN USA

The term "RESTORE" is a misnomer. You let the software extrapolate and create additional pixels by averaging adjacent ones. But these are estimations of what was really there, not truely restoring the original true resolution.

dsmeltz Loc: Philadelphia

And they have even given it a name. Computational photography. I mean really. That's OK for cell phones I guess.

imagemeister Loc: mid east Florida

There is NOTHING about digital photography that correlates strictly and absolutely with "reality" - it is ALL an interpolation/extrapolation !

The software does restore resolution - just not 100% fidelity. Is it acceptable for your image ?? - In most cases, it IS acceptable for MY images !

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imagemeister Loc: mid east Florida

It's OK for me - I am amazed by it ! (statistical analyses) - having application to every phase of our lives - and the basis for artificial intelligence - whether we like it or not !

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dsmeltz Loc: Philadelphia

I love statistical analysis! And modeling. Especially DEA. But the one thing we know about stats and modeling is the the fit is never perfect, it is an approximation of how things work that will, likely, be proven wrong in some major way at some point. However, until it is proved wrong and while it is useful at predicting things, we will continue to use it. After we find the error, we adjust the model.

Notorious T.O.D. Loc: Harrisburg, North Carolina

Digital is never analog but if we cut the pieces smaller and smaller we can get closer and closer perhaps. I worked in AI in the early 1990s and was not impressed and moved on. It is still programming, data and processing. Much like the Cloud is what used to be called data centers in my view. Others mileage may vary.

Notorious T.O.D. Loc: Harrisburg, North Carolina

There is an element of randomness that is hard to account for in life... If you played only the most drawn Mega Millions numbers would you win the billion dollars...probably not. But statistically you might improve your odds slightly...

abc1234 Loc: Elk Grove Village, Illinois

Why do you ask?

abc1234 Loc: Elk Grove Village, Illinois

Some would argue this point because when you cut small enough, you are in the quantum range with all of its looney laws. I guess it all depends upon how small your scissors is and when you tire of chopping.

BboH Loc: s of 2/21, Ellicott City, MD

I have never been able to get my head around the issue in the stream of thought that the loss of pixels upon cropping denigrates the resolution, quality of those pixels remaining in the image notwithstanding Burk's good explanation and PHRubn's following comment.
To make an analogy:
I have a jar of sliced peaches which I purchased because I like its taste (resolution) - the label advertises (x) number of slices (pixels). I dish out a serving and the reduction of the number of slices (pixels) does nothing to the taste (quality) of those slices (pixels) remaining; the taste (quality) is unchanged from what it was before the jar was opened. Another - I have a piece of 8x11 1/2 paper which I trim down to 6x8 - the quality of the 6x8 is unchanged from what it was before it was trimmed out.
?????