How to work out crop ratios

LCPete

LCPete

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This is actually a basic maths question but it relates to processing so I’ll ask here
The images we take with our cameras our cameras are 18 by 12 ratio , I understand it’s 3 : 2 , my camera file size is 8192 by 5464 pixels

if I knew the 3 in the ratio for example 8192 how do I work out the 2 if I don’t know how many pixels ?

if I want to crop from that in photoshop to the same ratio I just put in 18 by 12 inches and crop to the size I want
if I want to do the same in Affinity photo its slightly different I use the setting original ratio or the setting unconstrained and put in the number of pixels for each side

if I do an image stitch of say 3 pictures and want to crop out of that file to an 18 by 12 ratio and I know the 3 the longest side is going to be 10458 pixels how do I work out how many pixels the shortest the 2 will be ?
hope that makes sense there’s obviously an easy multiplying formula for ratios but it’s been a long time since I went to school and was never any good at maths :oops: :$
 
Divide the number of pixels by 3 and multiply by 2. As long as you have enough pixels on the 2 side.
 
Erty said:
Divide the number of pixels by 3 and multiply by 2. As long as you have enough pixels on the 2 side.
Click to expand...

thank you that’s great , thought it wasn’t too complicated that helps me a lot :)
 
I did look on google but just ended up confused :oops: :$

I don’t have photoshop on the computer that I do my editing on ( MacBook) , I use Affinity photo , which for most things I prefer but occasionally do photo merges , stitch several shots together, normally taken with tele lens
to crop those images to the 3 : 2 ratio at the moment I’m using an old version of photoshop on an old pc , but now will be able to do this on affinity thats made my life much easier, thanks again :)
 
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Isn't there a modifier key so that you can drag the crop rectangle without changing its shape?
 
Craikeybaby said:
Isn't there a modifier key so that you can drag the crop rectangle without changing its shape?
Click to expand...

didnt know about that will have a look
if I have an file / image that is 3 or so shots that I have stitched together they will most likely be an uneven ratio ,what I am trying to do is take an 18 by 12 (3 :2 ratio ) (or 12 by 18 ) crop out of that image
as Andrew explained when I have decided on the number of pixels on the longest side i need to divide the number of pixels by 3 and multiply by 2.
As long as I have enough pixels on the 2 side.
 
Hi Pete, look for the cog button when crop tool is active it'll give a drop down menu of ratios (in Affinity)

Crop tool

 
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