Understanding & Correcting Image Size in Photoshop

Resizing an image to use for a Photopolymer plate, or to print, seems to be the hardest thing for people to get their head around.

When I first started to learn Photoshop, I found it impossible to understand, several teachers had tried to explain it to me, but I got totally lost in the jargon, heck, I didn’t even know what selecting an image meant!!

Things changed totally when I went to Art school, where they had just appointed a new tutor for computer classes, or ‘Creative Technology’ as they called it. This had been the most frustrating class up until then and all of us hated going. Then Paul came along and demystified everything to us Visual Artists, by showing us how it worked, not just talking at all of us sitting there with our eyes glazed over.

The most important thing to understand is the difference between the image’s Resolution and its Physical size.

So here is how he explained it to us, let’s leave the computer and get into the kitchen!


Size vs Resolution – How are they Related?

Sugar in Spoons and Image resolution: How are they related

Sugar in Spoons and Image resolution: How are they related?


Here you see 3 identical teaspoons

They all have a different type of sugar in them

The top one has coffee crystals = Big grains = fewer pixels

The middle one has normal sugar = Medium grains = More Pixels

The bottom one has caster sugar = Very Fine grain = Lots of Pixels

The Green arrow points to the spoon – this represents the image’s physical size – The Physical size is what you would get you print the image on paper.

The Red arrow points to the grains – they represent the Resolution
Resolution determines the number of pixels in your image – they give you the amount of detail you can get.

So you can see the amount of detail changes when the resolution increases.
– but the size of the physical image stays the same!

So How do you relate that to an image in Photoshop?


The difference between Low & High resolution images

The difference between Low & High resolution images


Here is the same fingerprint:

  • At the same Physical size – just under 1 inch high
  • At different resolutions – 300 & 72 Dpi

As you can see the detail one print  is detailed and crisp – it’s displayed at at 300 dpi – more grains – pixels – are available to get more detail into the image

While the print with the green arrow – at 72 dpi – is unclear and fuzzy – less grains available to make the image clear.

So here is what we will do in Photoshop to Fix this


Image Size for fingerprints in Photoshop

Image Size


  1. Scan your fingerprint at 300 dpi
  2. Open the image in Photoshop and crop it fairly close to the print
  3. In the Menu bar got to Image -> then click on Image size
Changing the image size - step 1

Changing the image size – step 1

Changing the resolution – Step 1


In the pop up dialogue box you will see the Physical size and the resolution of the image as Photoshop sees it now.

As you can see it came in at a weird resolution so we need to change this and get it back to 300 Dpi.

NOTE: Look at the Physical size – it is well over 2 inches! WAY too big!

This is what we are going to fix in the next step.

  1. Changing the image resolution - step 2

    Changing the image resolution – step 2

    Make sure ‘Constrain Proportions’ stays ticked

  2. Untick the box ‘Resample Image’
  3. Type ‘300’ into the Resolution box

NOTE: See how Photoshop has changed the physical automatically, back to the size we originally scanned the fingerprint?



The Finished Fingerprint Image


The Final Cleaned up Fingerprint

The Final Cleaned up Fingerprint


So here is the finished print, all done and ready to use!

If your print needs more cleaning at this stage, check out my Video tutorial here:


Hope this gets you out of trouble if you ever have a strange resolution come through.

Let me know if you have any problems with this?

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