# Resizing image to real world dimensions

this may sound like a really amateur question but I'm trying to resize some images to dimensions in centimetres (10cm height x 15cm width to give you an idea), but upon changing two photos to the same centimetre dimensions, I notice they have completely different pixel dimensions? Am I doing it wrong or is this meant to be this way. Thanks

• Are you `Resampling` when you change dimensions? Commented Jul 30, 2015 at 18:20
• Yes, as I can't achieve 10x15cm when I uncheck resample because it automatically changes the sizes based on whatever I put in
– Ali
Commented Jul 30, 2015 at 18:22
• You can print an image at a certain size, and an image can have a certain number of pixels. If your images have different pixel dimensions at the same physical size it simply means that one image contains fewer pixel in the first place.
– DA01
Commented Jul 30, 2015 at 19:40
• Is the resolution the same between the images? Commented Jul 30, 2015 at 22:27

Simple ratio: PPI = Pixels per inch

Same centimeters with different number of pixels mean different densities of said pixels. The denser the pixels, the highest the quality (resolution). So one of your images might be 72ppi while the other might be 300ppi.

• One image resized to 10x15 turns out like this prntscr.com/7yxa08 - the other turns out like this: prntscr.com/7yxanl
– Ali
Commented Jul 30, 2015 at 18:21
• I specified 72 PPI on both images when resizing, yet they still have different dimensions in pixels, will they both print 10x15cm ?
– Ali
Commented Jul 30, 2015 at 18:21

First understand that `resolution + width + height = Print size`.

You can't change the left side of the equation and expect the right side to stay the same. From the sound of things you are trying to alter the width, height, and resolution but retain the print size. That's why you are struggling.

If you are not printing these images, the `resolution` field means nothing. See Here

If you are intending to print these images, then you want a minimum of 240PPI in the resolution field and you do not want to `Resample` when changing the width and height. This often means you get a width and height (print size) which is different than you anticipate.

When you uncheck the `Resample` option and subsequently alter the `Resolution` of an image, Photoshop does not generate new pixels (interpolation). It merely changes the density of the existing pixels in the image. This is done to keep the image quality the same. However, in order to do this the width and height must change to match the new pixel density of the image.

You can do what you are trying to do. However, it is not recommended for print-destined images, and you have to do it in 2 stages....

# WARNING: This often results in low quality images.

• `Image > Image Size` check `Resample` and set the `Resolution` to 240PPI. Then click `OK`.
• `Image > Image Size` uncheck `Resample` and input the `width` and `height` you want. Then click `OK`.

This will get you images at the dimensions you want and the resolution you want. However, chances are very high that the images will not look as good as you think they will. Doing this often results in degradation of the image overall.

# WARNING: This often results in low quality images.

While I point out the steps above, you should reexamine the images afterward to ensure they still appear suitable for reproduction. These steps are inherently bad to perform on most print-destined images.

• Why the down vote? Commented Jul 30, 2015 at 19:53