# What is the formula to upscale a photo?

Say I have an photo that is 2000 x 3000 pixels. I want a large print that is 20 inches by 30 inches. That means it will be 100 PPI.

I’ve been told to upscale my photo before getting it printed. Why?

What do I upscale the photo to precisely? What’s the formula to upscale a photo?

• This is not answerable without referring to your other question, & even then the answer will depend on what software you own, or are willing to purchase. 'Good' upscaling uses AI-type structures. 'Cheap' upscaling is a fairly pointless exercise. Why don't you let the print shop do it, at least they know their own system. You're going to be guessing. Jan 6, 2022 at 17:59
• Does this answer your question? Is there a general formula for image size vs. print size? Jan 6, 2022 at 17:59
• Yes, that explains it. Cheers. Jan 6, 2022 at 20:29
• Does this answer your question? How can I upscale a low-res image to make it appear higher-res? Jan 8, 2022 at 22:37
• Jan 8, 2022 at 22:38

I’ve been told to upscale my photo before getting it printed

It is a recommendation. You do not have to if you do not want to. The point, in reality, is if you actually know how a 100PPI image looks like.

100PPI means that you have a little square of 1/100 of an inch. You might see them or not, depending on the viewing distance and the print quality. But also on the detail of the image. You normally see these pixels on a diagonal sharp line. They will look like a saw.

Upscaling it to the exact double, will give you 200PPI, which is normally enough even for close distance viewing. It will diffuse the pixels, which normally is less distracting than seeing the saw line.

Here is a specific example.

The dot on the top is the original size.

And on the second row, I used 3 different methods of resizing. The first one is just upscaling the original image, so you see the same pixels just bigger. That is what you would get, not only if you do not rescale the image at all, but if you could actually see the individual pixels, depending on the distance, but say around 100PPI.

The other two are using different resampling methods, In the second one, you can see the effort to blur the rough squares averaging the value of these new pixels. Probably the third method did a better job.

Some new AI methods try to guess what is the original directionality of a pattern and line. If the algorithm worked ideally, they would get something like the third row. Which in my case is only a fake example. I used a vector shape for the last row.

They are asking you to resample because they want you to make the decision on which look you want, in the case the pixels are distinguishable.

• If you don't, you'll force the print house to do the upscaling. They might not use the method or level of care you expect. Jan 7, 2022 at 18:32