Sunday 28 November 2010

PP Tips 13 - Resizing An Image - Up

This is part of a 'How To' series on post process work.

This is Photoshop specific, but most good editors work in a similar manner.

Note - You really need pay attention here as there are many complicated steps  !?!? Joking

Here, I am (re)sizing an image from it's base 9.6 x 12.8 inches size, to 30 x 40 inches. In other words, I am sizing it 'up', and a long way up at that.

It is not that I would print this particular image at that size, but I chose it as an illustrative example as it is clear and sharp.

Note : This is about sizing 'up', not about cropping. I will cover that in another topic

First things first. Do any editing work first. If your monitor resolution is setup correctly, for Photoshop, then if you view the image at 100% for, say, a 9.6 x 12.8 inch print such as mine, you will be viewing it as if it would print at 30 x 40 inches

With the base image I am using, it is 3840 pixels (picture elements) by 2880 pixels. My 23 inch monitor resolution is 96 (95.78) pixels per inch (PPI) and if I divide the image pixels by 96, I get 30 x 40 inches. 3840/96 = 40, 2880/96 = 30.

Similarly, if viewed at 50%, it is as if it would print at 15 x 20 inches. If it looks poor at 50%, or at 100%, it will also look poor printed at these large sizes.

To calculate your own monitor PPI, click here for a simple, but very effective, calculator.

As an example, my own monitor calculation.

Knowing that the monitor PPI is 96, in Photoshop I click Edit/Preferences/Units & Rulers and enter my monitor PPI in the Screen Resolution box.

Note : Use the calculator as it will give you an accurate number based on all your screen criteria. Photoshop's default value is 72 PPI

OK. Here is my base image. Nothing exciting, but it is clear and sharp. Besides, I couldn't afford a professional model.

Note : Clicking on any image will take you to a larger size of that image. Detail is a little hard to see at the sizes displayed here

So, how would I resize this image from 9.6 x 12.8 inches to 30 x 40 inches ?

It's very simple. I select Image/Image Size and enter my new values. I make sure the Resolution is still 300 pixels/inch, Constrain Proportions is checked and I use Resample Image : Bicubic Smoother.

You think I'm joking ? Well, actually I'm not. I do this in practice all the time.

However, let's dig a little deeper.

First, let's look at the detail in my original 9.6 x 12.8 inch image, and if viewed at 100% (30 x 40 inch print equivalent).

Second, let's look at the detail in the image, after resizing to 30 x 40 inches, and if viewed at it's new actual print size.

See the difference ?

Let's look a little closer.

At left, my new resized image shown at print size. At right, the original viewed at 100%.

If you read some articles, you will find many different opinions on how to resize an image. Some have merit, some are rubbish. I'm being polite.

I am not saying that the way I describe is the only way, nor is it the absolute best way, but it works for me and most of my associates do the exact same.

I run a gallery and print anywhere between 8 x 11 inches to 30 x 40 inches. My typical largest size is 23 x 32 inches, and 30 x 40 inch is an occasional size. However, the principles are the same for upsizing for any size larger than the base image size.

Anyway, let's look a little further at some different options in Photoshop.

Example 1
One oft touted method is to upsize the image in incremental steps. In other words, upsize the base image a little, then upsize the result, and repeat, etc., etc.

In fact, I used to do this religiously, until one day I really had to ask myself - Why ?

For the example I show here, I used 'Bicubic Smoother' and incremented in the following steps :

Base - 9.6 x 12.8 inches
Step 1 - 12 x 16 inches
Step 2 - 16 x 21.333 inches
Step 3 - 22 x 29.333
Step 4 - 30 x 40 inches

You can use many more 'steps' but, in reality, it achieves little, if any more than the steps I have shown.

At left is detail of the image which I simply upsized to 30 x 40 inches. At right, the 'stepped' image.

Note : The right hand image is flipped horizontally for comparison purposes

Example 2
The same as the above, but this time I have simply used 'Bicubic', as opposed to 'Bicubic Smoother', for my image resampling.

Example 3
Again, the same except that I have used 'Bicubic Sharper' for my image resampling.

Anyway, That's it. Hope you find it helpful.

Note : After resizing, at times I will add a little more sharpening. It is purely image dependent. Remember that with today's monitors, the image will appear sharper on screen than when it is actually printed


Other posts in this series - Click here for the index page.



  1. Amazing stuff Lloyd... an eye opener!
    Lost all my favorite sites when windows played up and I re installed.
    Found you again at last.
    your stuff is wonderful.
    Do you ever do workshops or such?.
    I travel a bit...
    Thanks again for your insights...

  2. Kerry, Hi.

    Thanks for the comments. If you're ever around, look me up and I'll give you some pointers.



  4. Dang this is awesome Dave. I never thought you could achieve such perfect detail at resized resolution. Thanks for sharing.

  5. Joms, Hi.

    Thanks for the comment. Unfortunately, some like to cloud the whole subject but really there is nothing difficult about it.


    PS - If you get a moment, send me an email. The address is in my DPR profile.

  6. Your blogs and its stuff magnetize me to return again n again. ppi calculator

    1. Robert, Hi

      Thanks for the comment and glad you find it helpful.