How to change my file from A3 to A2 and keep the best quality?

Question

I'm making a poster which at first I had intended to print in A3 size. So I created a 300dpi photoshop file with 297mm x 420 mm which is 4961px x 2508px.

Now, I'm thinking I want to print it at A2 size. So I guess one option is to keep creating the file at 4961px x 2508px, and print it scaled. Am I right that this will be 150dpi and therefore wouldn't be noticeably any worse quality because quality printers have a maximum of around 150dpi.

The file contains many png images. Most of which are scaled down a lot, so if they were to be doubled in size, they wouldn't be any lower resolution.

Or is there a way to scale my photoshop file and have all the layers and objects be redrawn so they are at the best quality?

What's the best way to do this?

Kevin Stohlmeyer · Accepted Answer

Hi @alfie285769162t0j

This page gives an overview of options:

https://helpx.adobe.com/photoshop/using/resizing-image.html

There is also the SuperZoom Neural Filter, you can create a smart object combining all your layers then enabling that feature to help with the low res layers.

https://www.youtube.com/watch?v=bL-x6GIDL7o

davescm · Answer

The file contains many png images. Most of which are scaled down a lot, so if they were to be doubled in size, they wouldn't be any lower resolution.Yes they will, unless those higher resolution images have been placed as Smart Objects. Ordinary layers are scaled down and the excess information discarded, so scaling back up does not replace that information. That said you have two choices.1. Increase the size without resampling which will give 150ppi. That has the advantage that no scaling artifacts will be introduced but there is a small risk that when viewed very close then the pixel structure might be visible. However you really would need to stand close - good eyes could resolve 150ppi at 45 inches whereas 300ppi would be 23 inches. (both are the equivalent of 60 lines pairs per degree). 2. Resample to A2 at 300ppi. That does not replace missing picture information, although placed smart objects will be recalculated,  but interpolates the missing data from that image data which exists. Different algorithms do that in different ways and some can look good. All though do introduce their own artifacts. Whether they are obtrusive depends on the content. Dave

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