Cropping - How could I best quantify it?

[Ross Taylor]

I have been quantifying my crops as a percent of frame width. That seems to give a good idea of how much I cropped assuming my 3:2 aspect ratio is preserved.

If I crop a pano from a 3:2 image, % frame width does not convey how much of the image I actually cropped out.

It seems to me that area, width x height in pixels, should factor in to how I describe my crops when posting.

Is there a commonly understood way to describe the degree of cropping that I could use?

Thanks so much for considering my question,

Ross

[David Cowling]

Good question Ross. I am afraid that I cant give you the answer but it is something that I am also interested to know.

[arash_hazeghi]

There is no commonly used terminology, most folks usually use one side only. For e.g. when they crop a 5000 pixel wide image to 2500 pixels, they call it a 50% crop, while in reality as you noted, the image only contains 1/4 of the original pixels or data so it is really a 25% crop.

The crop percentage is also misleading in that the final image size greatly depends on the camera, for e.g. a 50% crop from a 5DSr camera contains more than 25 Mpixels. That is more than a full frame image from a 7D2 for example.

[Ross Taylor]

Hi Arash,

Thank you for pointing out the ambiguity in quantifying crop as a percentage.

I suppose mentioning eg: Cropped 14M px from 22M px would be more meaningful, but reporting a crop as such would be uncommon.

Thanks so much for your answer, Arash. I thought I may have been missing something :)

Ross

[Daniel Cadieux]

Hey Ross, if you have time to spare there was a fun thread on this very subject a few years back. Check it out at the link below:S3:

http://www.birdphotographers.net/forums/showthread.php/67504-How-Much-of-a-Crop-Part-II?highlight=lasagna

[Diane Miller]

I didn't slog through all of that very long thread -- but there is one answer that is both accurate and simple.

Calculate the percentage by dividing the number of pixels in the cropped image (easily seen in Lightroom) by the number in the original. You'll get a fraction, such as 0.5 for 50% of the pixels remaining. So multiply by 100 to get a percent.

Then express the crop as a percent of the ORIGINAL or FULL FRAME file. Unambiguous.

[Ross Taylor]

Thank you so much Diane, Daniel, and Arash.

Your help, and the old thread really helped put this topic in perspective for me. Very much appreciated.

One unexpected "Eureka Moment" for me was in one of Arash's posts on the thread Daniel referenced:
"The main reason that cropping doesn't yield good results is lack of sharpness in the original file, many people struggle to get a photo that is tack sharp when viewed at 100% size, especially if is BIF. photographs that have sub-par sharpness or are noisy at full size cannot be cropped much without noticeable loss in IQ. If a photo is pin sharp and clean you can crop the heck out of it and it will still look good, on the web and printed. I have printed 2 mpixel crops from 5D2 at 12"X8" and the quality is just awesome :)"

I have been limiting my crops by percentage alone, disregarding anything that falls under 65% full frame width. Today I very closely examined different crops of my first Snowy Owl shot. Focus was tack-sharp and ISO was low at 320. The IQ seems consistent all the way down to 35% original frame width (a 2.7 Mpx image from 20 Mpx). This was really enlightening to me :)

Ross

[David Stephens]

There is no commonly used terminology, most folks usually use one side only. For e.g. when they crop a 5000 pixel wide image to 2500 pixels, they call it a 50% crop, while in reality as you noted, the image only contains 1/4 of the original pixels or data so it is really a 25% crop.
.

Not being argumentative, but I think of that as a 75% crop.

[Diane Miller]

This semantic uncertainty is why I suggested stating the crop not at "% crop" but as "% of the original full fame." There is no ambiguity there.

[David Stephens]

This semantic uncertainty is why I suggested stating the crop not at "% crop" but as "% of the original full fame." There is no ambiguity there.

I like that. You'd do it as a percentage of the total pixels, not the percentage of the long side, correct?

[Diane Miller]

Yes, percentage of the area. (See Pane 6.) And then state it not at "xx percent crop" which is still ambiguous, but as "xx percent of the full frame." That should imply area, but it could be stated to be even clearer.

[Glennie Passier]

Thank you Diane! I've been scratching my head about this for a while. Now It's quite clear.