Working out aspect ratios and changing them in PS

[g1]

Hi, can anybody explain in basic maths please, about how you work out

aspect ratios from the images dimensions? I understand what aspect

ratios are [ie the relative proportions of height & width] but I

cannot translate the 3:2, 1:3 etc to actual image sizes and vice

versa. Also, if anyone could tell me the simplest method of changing

the aspect ratio in PS I would be most grateful. Thanks in advance.

[JeffOwen]

There is no easy way to describe ratios, but if you divide the larger number by the smaller e.g. 4950 by 3300 (typical pixel count) then you get 1.5. this is the same as 3:2 (divide larger by smaller).

If you want a ratio of say 4:3 this gives 1.3333, use this number to multiply the smaller of your pixel count e.g. 3300 X 1.3333 to give the new number of 4400 which will be your pixel count at this ratio. By using the print size, inches or mm to find what ratio you need, e.g. a print of 11 by 14 has a ratio of 1.2727 i.e. a pixel ratio of 3300 by 4200. In PS I always use the 'print with preview' and the 'scale to fit paper' selection to automatically get my print to best fit on the paper I have selected. I hope I haven't got you too confused.

[klaus.sailer]

The selection tool in PS lets you enter an aspect ratio. If you then try to select a region of your image, the selection is constrained to the ratio you have set. This way you can crop off regions of your photo to get the aspect ratio you want. Or you can use the info panel during the selection to get an idea about the numbers corresponding to an aspect ratio... in case you want to scale the image instead of cropping.

[g1]

Thanks for taking the time to explain Jeff. It sounds great but it all went over my head. I'm afraid I'm a bit of a maths dunce and even in your 'for dummies' version I still didn't get it. :( The reason I wanted to know the workings is because my camera format is 2:3, and for a competition I am entering, it asks for ratio 1:3 landscape or 2:1 portrait.

 

Thanks also to Klaus, I will have a look at the options in the crop tool dialogue.

[g1]

ps The pixel dimensions straight out of my cam are 3072 x 2048.

[dave_nelson___atlanta__ga]

You can use the Marquee Selection tool to crop your images in a desired aspect ratio. In PS 7 or higher select the "Rectangular Marquee Tool (M)" and in the "Options" toolbar you can select a "Style" of "Fixed Aspect Ratio" which will give you the opportunity to enter a width and height.

 

Enter your ration then using the marquee tool draw a rectangle on your image. When it is postioned you can choose "Image > Crop" to crop the image.

[leonard_evens]

Jeff explained it quite well. It is not actually that difficult, but if you have a lot of trouble with simple arithmetic, then you might be better off trying to let Photoshop do it for you.

 

Whatever you do, keep in mind that your camera is producing images in one aspect ratio, and in order to produce something with a different aspect ratio, either you have to distort the image or you have to crop it. I strongly recommend against distorting it. I recommend cropping instead.

 

Let me try to do the calculations for you. You are starting with an image of size 3072 x 2048. Let's suppose it is basically in landscape mode. If you want to submit it in 3:1 aspect ratio landscape mode, you have to change the short (vertical) dimension. It is now 2/3 or the long side. You want it to be 1/3 of the long side. So it will have to be half of what it currently is. That means you have to crop your image so it is 3072 x 1024. (note 1024 is 1/3 of 3072.) How you crop it is up to you.

 

Supposed on the other hand, that you have an image which is 3072 x 2048 in portrait mode, so the long dimension is the vertical dimension. You want to submit something in portrait mode with aspect ratio 2:1 of long to short side. That means the short side has to be 1/2 of the long side. That means you should crop horizontally so the resulting image is 3072 x 1536.

 

Of course, there are other possibilities. You might also want to crop the long dimension. You can do that, but when you are done, you should also crop the shorter dimension so that in the landscape case, it is 1/3 of the long dimension and in the portrait case, it is 1/2 half of the long dimension.

 

If after some study, you still can't figure it out, you might try to find someone else who can do arithmetic who will do it for you.

[g1]

Thanks Leonard. I'm pleased to say I followed that a little easier. I appreciate your time and explanation!

 

Thanks also to Dave.