Scale image

[mmjoshi]

GIMP Version: 2.10.32
Operating System: Windows
GIMP Experience: New User

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I have a tiff image with 3116 x 4680 pixels and a resolution of 72 DP.I This gives a print size of 43.28 x 65.00 inches which is too big and at a resolution of 72 DPI will result in a poor print. I would like change the DPI to 300 AND the print size to 24 x 36 inches. Is it possible to do this with minimal quality loss and still get a good print quality?

[sallyanne]

Unlikely, since it is such a small dpi to start with

[Blighty II]

You can use (Image > Print Size) to see the relation between print size and dpi.
(The pixel size stays 4680x3116)

For a 36x24" print you get 130dpi. You will need a larger image in pixels to get 300dpi.

[ofnuts]

GIMP Version: 2.10.32
Operating System: Windows
GIMP Experience: New User

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I have a tiff image with 3116 x 4680 pixels and a resolution of 72 DP.I This gives a print size of 43.28 x 65.00 inches which is too big and at a resolution of 72 DPI will result in a poor print. I would like change the DPI to 300 AND the print size to 24 x 36 inches. Is it possible to do this with minimal quality loss and still get a good print quality?

https://www.gimp-forum.net/Thread-Image-size-in-Gimp

[mmjoshi]

@sallyanne, @Blighty II and @ofnuts, thanks for your responses. The article sent by @ofnuts is interesting information. Will go through it in detail.

As I understand, the print size in pixels and the print resolution are interdependent. If one needs to increase the print size the resolution by definition has to decrease and vice versa. Am I correct?

Can the print size AND the resolution both be changed by using the Image|Scale image option? Apparently one can change both by using this command. Also, there are multiple Interpolation options like Linear, Cubic, NoHalo, LoHalo etc. What effect do these have? As I understand, to increase the print size and/or the resolution Gimp, will have to add pixels which were not there in the original image thereby reducing the quality. Was wondering how bad this could be.

I am printing an image from Gimp for the first time and hence the confusion!

[rich2005]

Can the print size AND the resolution both be changed by using the Image|Scale image option? Apparently one can change both by using this command.

It can, the trick is set the pixels-per-inch (ppi) before touching the width / height setting.

30 second animation of that https://i.imgur.com/fh1DNUc.mp4 and Gimp will do the calculations as well.

Also, there are multiple Interpolation options like Linear, Cubic, NoHalo...

Use the most modern option NoHalo.

...but up-scaling to 24x36 @ 300 ppi is about 230% and for poster sizes photographic quality 300 ppi is not always necessary since viewing distance comes into play. see: http://resources.printhandbook.com/page ... inting.php

There is an equation for ppi(dpi) taking a viewing distance 36" DPI = (1 / ((36*.0.000291) / 2))
Just looking at a similar size print you would not normally be much closer and that gives a ppi of about 190 say 200 ppi. A scale factor of 150% a bit more reasonable.

The other thing to consider if sending to a commercial printer, let them do the scaling, their printer scaling algorithms every bit as good as Gimps.

[mmjoshi]

@rich2005, great information. My idea for making a large print was to submit for an exhibition at my local photo club. I agree that the viewing distance is unlikely to be less than 36", in which case a DPI of 180/200 should be adequate. This will require less up-scaling thereby minimizing the loss in quality.

Thanks for the tip on using the Image|Scale image option. Very helpful.