Understanding of Cropping vs Resizing of images

JoeB94

Member
Joined
Jul 16, 2020
Messages
73
Hey all, so I have been doing some playing around and realised that I don't truly know the difference/corrolation of Cropping & Resizing or what they really do to an image.

So I have done some self research and want to check if my understanding is correct....

RESIZING:

The resizing of an image, is when the software changes the physical dimensions & the weight of the image from its original size to fit a certain space available, by scaling (re sampling) down the number of megapixels used in order to show the image within its new dimensions that you require, constraint to the same current aspect ratio of the image, otherwise if you tried to change the aspect ratio by using the resize tool, then the actual images would become distorted (squished together) and this is why most processing software, only allows constraint resizing.

So an example would be if I re size my 20mp image currently at 5184mp on the long edge. to say 2048px on the long edge, then my software will scale down the number of megapixels available from 20mp relatively, to the new dimensions, but using the current aspect ratio. However with resizing because you now have less megapixels creating the image, you end up with a less clear image if you zoom in to the smaller dimensions, than you would the larger, due to less megapixels available to render the image... however the advantage of resizing is the image is smaller physically & in file size (weight) which is better for online use/upload. And also why certain website have certain dimensions it can take due to file size and physical viewing space available to use.


CROPPING:

So cropping on the other hand does not change the physical size of the image, as it does not scale or re sample the image down. What it can do is change the viewing dimensions, by removing any image (pixels) you don't need, in order to focus the subject of the image better and this is done by changing the aspect ratio of the image, essentially changing the ratio between the long edge and the short edge (L X W) dimensions... But when you crop an image, you don't lessen the actual number of megapixels, because your not scaling down or resampling the image like you do with resizing above, you are just changing the megapixels that are in view.


RESIZING & CROPPING:

The reasons you may use both together, would come to an example I had from yesterday. I needed an image for instagram, that required dimensions/weight of 1080 x 1080px... But If I just resized my image to this, I ended up with an image at 1080px X 7..px & I now see this was because, if resizing hadn't been constraint to my original non cropped ratio, then my image would have become distorted (squished together), as it would try to show the whole image in these measurements, so this is where you would crop first to change the aspect ratio to 1:1 but loosing some of the image, but when resizing you would not cause distortion. But as your doing both, you may suffer a bit of image quality loss, as apposed to if you either copped with no resizing or resize but using the original aspect ratio (no crop).

____________________________________________________________________________________________________________________________________________________________________________________________

And the final part is resolution but I think im right in saying I don't need to worry about resolution (ppi) for digital use, as this only comes into the mix when printing, which im not.

So I hope I have finally got the idea of how it all works! Thank you :)
 

JoeB94

Member
Joined
Jul 16, 2020
Messages
73
Hey all, so I have been doing some playing around and realised that I don't truly know the difference/corrolation of Cropping & Resizing or what they really do to an image.

So I have done some self research and want to check if my understanding is correct....

RESIZING:

The resizing of an image, is when the software changes the physical dimensions & the weight of the image from its original size to fit a certain space available, by scaling (re sampling) down the number of megapixels used in order to show the image within its new dimensions that you require, constraint to the same current aspect ratio of the image, otherwise if you tried to change the aspect ratio by using the resize tool, then the actual images would become distorted (squished together) and this is why most processing software, only allows constraint resizing.

So an example would be if I re size my 20mp image currently at 5184mp on the long edge. to say 2048px on the long edge, then my software will scale down the number of megapixels available from 20mp relatively, to the new dimensions, but using the current aspect ratio. However with resizing because you now have less megapixels creating the image, you end up with a less clear image if you zoom in to the smaller dimensions, than you would the larger, due to less megapixels available to render the image... however the advantage of resizing is the image is smaller physically & in file size (weight) which is better for online use/upload. And also why certain website have certain dimensions it can take due to file size and physical viewing space available to use.


CROPPING:

So cropping on the other hand does not change the physical size of the image, as it does not scale or re sample the image down. What it can do is change the viewing dimensions, by removing any image (pixels) you don't need, in order to focus the subject of the image better and this is done by changing the aspect ratio of the image, essentially changing the ratio between the long edge and the short edge (L X W) dimensions... But when you crop an image, you don't lessen the actual number of megapixels, because your not scaling down or resampling the image like you do with resizing above, you are just changing the megapixels that are in view.


RESIZING & CROPPING:

The reasons you may use both together, would come to an example I had from yesterday. I needed an image for instagram, that required dimensions/weight of 1080 x 1080px... But If I just resized my image to this, I ended up with an image at 1080px X 7..px & I now see this was because, if resizing hadn't been constraint to my original non cropped ratio, then my image would have become distorted (squished together), as it would try to show the whole image in these measurements, so this is where you would crop first to change the aspect ratio to 1:1 but loosing some of the image, but when resizing you would not cause distortion. But as your doing both, you may suffer a bit of image quality loss, as apposed to if you either copped with no resizing or resize but using the original aspect ratio (no crop).

____________________________________________________________________________________________________________________________________________________________________________________________

And the final part is resolution but I think im right in saying I don't need to worry about resolution (ppi) for digital use, as this only comes into the mix when printing, which im not.

So I hope I have finally got the idea of how it all works! Thank you :)
I need to add that under cropping it supposed to say DOES/CAN change physical size!
 
Joined
Nov 27, 2013
Messages
1,570
Location
Queensland
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I think you pretty well have it sorted!
I like simplified explanations!!
Here is an image-
ScreenShot099.jpg


Here is a Crop-
ScreenShot100.jpg

Here is a Resize (DOWN!) to a smaller Pixel size-
ScreenShot101.jpg
 

JoeB94

Member
Joined
Jul 16, 2020
Messages
73
I think you pretty well have it sorted!
I like simplified explanations!!
Here is an image-
View attachment 15993

Here is a Crop-
View attachment 15994
Here is a Resize (DOWN!) to a smaller Pixel size-
View attachment 15995
Ahh brilliant! I’m glad I am understanding thing along the right lines & haveing you picture as a visual example just concretes it for me!

Thank you very much for offering those, very much appreciated. Also a lovely image too :)
 
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