How to Resize Images
in Adobe Photoshop
How best to resize images?
Yes, there are even things to learn with this apparently simple step in the digital photography workflow!
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At a time when so many visitors are submitting photographs that need to be perfectly optimised for my Free Photography Contests and for Free Photo Sharing, the following will be helpful...
It's incredible how much such a small box can control!
Hopefully, you have read my recent article What is a Pixel? in which I describe the humble pixel as the smallest editable component of a digital file?
Well, the Image Size dialog box (Image>Image Size) controls exactly:
1) How all those pixels are defined and sit together;
2) How often the pixels occur over a certain distance (the resolution, usually measured in pixels per inch)
3) How many pixels there are in total.
A Collection of Photoshop Actions for You...
Read on to follow the step-by-step guide.
However, for those of you familiar with Adobe Photoshop Actions, I have made a collection of three Actions that resample your files to a choice of 500, 600 or 1000 pixels at 72ppi.
They prepare everything for you in moments at the click of a button!
Then visit my Collection of Downloadable Actions and download it in just a few clicks.
If you aren't familiar with Photoshop Actions and have always wondered how to use them, I have also recently published an easy-to-follow eBook on this powerful Photoshop feature.
On with the tutorial on how to resize images in Photoshop...
If we increase the file size, the number of pixels increases (the megabyte size increases).
This is simply because there is more information to describe within the file. Increasing the number of pixels is known as resampling or interpolating.
Likewise, if we reduce the file size, the number of pixels decreases. This is known as resizing.
Now, this is what I would like you to learn today:
Photoshop doesn't just resample or resize images randomly!
It cannot make information out of nothing...Photoshop has to be given guidance.
It uses clever, complex strings of instructions (algorithms) to make an educated guess as to which pixels to add or throw away in the resampling/resizing process.
Did you know that you can choose between five different methods in both Photoshop AND Photoshop Elements?
They appear in the drop down menu at the bottom of the Image Size Dialog box. Here they are again for you:
I would like to concentrate on two of these for the moment...
Making Images Larger?
To obtain the best results when resampling images (making them larger), select Bicubic Smoother.
A typical instance for resampling a digital photograph often occurs when making large format prints.
Modern printing equipment can make the most extraordinary prints but only if they are given the correct amount of data in the first place!
In most cases, you should be able to make the size increase in one step. Simply type in the dimensions you require, select Bicubic Smoother and click OK.
TOP TIP: Change the units to Percent to see how much larger the increase will be:
In the above example, I would like to make a print of the kayak image roughly A3 in size at 300ppi.
The original file from the compact camera I used is only 14.4MB.
At the top of the Image Size dialog box, I can see that the new file size will be 52.8MB but how much is that increase?
I can find out easily by changing the units in the top portion of the box from Pixels to Percent.
Photoshop tells me that this increase will be 191.38%.
In my experience, an increase in size of around 200-250% is absolutely fine to carry out in one step.
When resampling by a very large amount, however, it may be a good idea to consider increasing the file size incrementally.
25% at a time is a good starting point until you get near your final size requirement.
For example, it may be that you increase the file size by 25% as many as five or six times and then, as the last resampling step (which will be less than 25%), type in the exact size required.
It keeps the figures easy for Photoshop to compute...a 25% increase turns four pixels into five pixels. It can make a pretty good guess as to what that fifth pixel should look like based on the appearance of the other four.
Remember, to increase the file by 25%, you actually need to type 125% into the appropriate field:
Making Images Smaller?
To resize images (make them smaller), select Bicubic Sharper.
Selecting this algorithm introduces appropriate amounts of sharpening to all the remaining pixels that haven't been thrown away by Photoshop.
This avoids reducing the file to little more than a hazy mush!
Again, it's usually the case that you can resize images in one manoeuvre.
In the rock and roll days, before Bicubic Smoother and Bicubic Sharper were introduced, I often used to resize images incrementally by using the Bicubic algorithm.
It's rarely the case in the modern era, however, that I see the appearance a file improved by being incrementally resized.
As the final step, a little judicious sharpening usually tops the process off nicely but more on that another time!
So, in summary...
Smoother = Bigger
Sharper = Smaller
State Your Preference...
The default method of resizing/resampling can be set in Photoshop's General Preference pane.
For example, if you find you normally resize images, then select Bicubic Sharper as the preference.
As a result, this will always be the first option that appears when you open the Image Size dialog box.
This facility isn't available in Photoshop Elements.
Transform, The Right Way...
When using Photoshop's Free Transform function, have you ever thought about how elements are being made larger or smaller?
Did you know that you can be in control of this too in order to ensure the best results?
You see, when Transforming or Free Transforming pixels (Edit>Transform/Free Transform), Photoshop takes its instruction on how to make the edit by looking to the Preference setting described above!
For example, when compiling the kayak graphic at the top of this page, my first task was to reset my Image Interpolation* setting to Bicubic Sharper.
This ensured that when I transformed the top layer to be smaller than the bottom (larger) layer, it would be carried out in the most appropriate manner!
[*This setting can actually be a bit of a misnomer because, as you will now from my Digital Photography Terminology page, interpolate actually means an increase in the quantity of pixels. If choosing Bicubic Sharper, you will, of course, resize images and decrease the quantity of pixels!]
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