Cropping Explanation

[Louis champan]

I would sure appreciate if someone could explain to me exactly what is meant by 50% crop, 100% crop. You see this all the time where someone says that this image was a large crop or it's a 60% crop. I have my own idea of what this means but would sure appreciate an explanation from someone that knows a lot more about it than I do.
Thanks
Louie

 

[bleirer]

The term is used different ways so it is confusing. To me a 50% crop means if my photo was 24 million pixels at 4000 by 6000 pixels and it is now has some of the edges cut off and now it is 12 million pixels at 3000 by 4000 pixels or any combination of width times height. But sometimes people say crop when they refer to the screen view. In that case if one pixel on the screen equals one pixel of the image then that is viewed at 100% but if one pixel on the screen is two pixels of the image, that is 50% view, sometimes called 50% crop view.

 

[Louis champan]

The term is used different ways so it is confusing. To me a 50% crop means if my photo was 24 million pixels at 4000 by 6000 pixels and it is now has some of the edges cut off and now it is 12 million pixels at 3000 by 4000 pixels or any combination of width times height. But sometimes people say crop when they refer to the screen view. In that case if one pixel on the screen equals one pixel of the image then that is viewed at 100% but if one pixel on the screen is two pixels of the image, that is 50% view, sometimes called 50% crop.

Appreciate your reply. I've always referred to crop size as the size I'm viewing the image at when I do a crop.
Thanks

 

[kimball]

"100% crop" is kinda meaningless. Strictly speaking it implies the resulting image is 0 pixels by 0 pixels. Taken more loosely, and as bleirer wrote, it probably is meant to imply that the image will likely be viewed by default at 1:1 (1 image pixel for 1 monitor pixel) on most normal monitors. But in all honesty the photographer doing the crop really doesn't have any control over what viewing magnification the end user happens to be applying, unless the photographer has embedded the image in a webpage or other document that can force a particular viewing condition.

"50% crop" (or anything less than 100%) is not a style of phrasing I recall seeing used. Perhaps you're thinking of a 50% re-size? Resizing an image so it's a smaller file that is made up of fewer pixels is of course not the same as cropping, which just discards whole chunks of the image (which in turn also causes it to be made of fewer pixels).

 

[pochito]

If I say "this is a 50% crop" I mean that I CUT the image by 50%, meaning that parts of the image (from the edges) are missing. Since my cropping does not necessary retain the aspect ratio, something like that would have no real use, at least from how I use it.

 

[kimball]

If I say "this is a 50% crop" I mean that I CUT the image by 50%, meaning that parts of the image (from the edges) are missing. Since my cropping does not necessary retain the aspect ratio, something like that would have no real use, at least from how I use it.

50% decrease in megapixels or 50% decrease in linear resolution? That's the rub. Those two different meanings will result in different crops, so it's unclear what 50% is referring to.

For example, if you have a 4k image (3840x2160) and crop it 50%, are you producing a 1080p image where each edge is 50% the length of the original uncropped image (1920x1080)? If so, that's a 75% drop in megapixels.

 

[Louis champan]

Thank you to all of you for taking the time to respond in such detail. Now I have to dig through this fully digest it for me to make sense of it.

 

[pochito]

50% decrease in megapixels or 50% decrease in linear resolution? That's the rub. Those two different meanings will result in different crops, so it's unclear what 50% is referring to.

For example, if you have a 4k image (3840x2160) and crop it 50%, are you producing a 1080p image where each edge is 50% the length of the original uncropped image (1920x1080)? If so, that's a 75% drop in megapixels.

Hmmm...
IMHO: It is just like taking a print, any size, any resolution and take the half of it with scissors. I crop the image, not the file.
You are right, the 50% crop has 1/4 of the surface of the original (i.e. 25% of the megapixels)
If you use the cropping tool for example in LR and "crop", this is what happens.
I personally don't see the utility of this info anyway, at least as I understand it.

 

[kimball]

I personally don't see the utility of this info anyway, at least as I understand it.

Agreed. I think most often people will list specific pixel dimensions when referring to the sizes of their crops. I’ve never really seen people speak of a percentage crop of an image outside of “100%” to imply a really drastic crop.

Then there’s the crop factor of sensors when discussing system equivalencies, but that’s a whole different can of worms.

 

[Louis champan]

I'm surprised, I've been asked and see others being asked, "how big of a crop was that image" and there's where my problems began. What I take from all of this discussion is a accurate reply to a question on cropping is just to state the pixel dimensions.

 

[kimball]

I'm surprised, I've been asked and see others being asked, "how big of a crop was that image" and there's where my problems began. What I take from all of this discussion is a accurate reply to a question on cropping is just to state the pixel dimensions.

Well, in my case I’m no authority. Just one opinion. I also tend to dislike heavily cropped photos so I may be inadvertently filtering out those kinds of conversations from my forum browsing.

 

[Replytoken]

I'm surprised, I've been asked and see others being asked, "how big of a crop was that image" and there's where my problems began. What I take from all of this discussion is a accurate reply to a question on cropping is just to state the pixel dimensions.

I agree. I usually reply with the pixel dimensions of the cropped image. I have never heard anybody refer to the file size when they are specifically talking about cropping.

--Ken

 

[Louis champan]

Again, I appreciate the discussion I think it's certainly brought more clarity to the subject for me.