Should you upsize crops? Which method?

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Digital Nigel Veteran Member • Posts: 7,897
Should you upsize crops? Which method?

We have frequent, long and sometimes heated debates on this forum on the merits or otherwise of CIZ vs crops that are not upscaled. So I decided to take and analyse some test shots yesterday.

First let's get the issue of cropping out of the way. I think we can all agree that many shots need to be cropped. Sometimes it's just to get rid of a bit of extraneous foliage, or if another tourist has strayed into the frame. But that's not what I want to discuss here.

The other form of cropping occurs when we reach the optical zoom limit of a lens, such as 72mm with the RX100M6 or 220mm with the RX10M3/4. Here, we may want to focus on only a small part of the image, perhaps a distant bird or wild animal. The rest of the image is of no interest, so we might want to crop very heavily, discarding most of the otherwise perfectly good image.

We now have an image that contains the subject we're interested in, but the resolution might have been slashed. We might decide that it's not a problem, and just use the cropped image as is. But, sometimes, the cropped image may be too small for our desired output device, which might be a high res screen or printer. We then need to upscale the image. This could be any ratio, but for the purpose of this test, I'm going to use a 2x upscale, which is the CIZ limit.

It's possible to do this upscaling in the camera or in post-processing. I've looked at both. When you upscale in post-processing, you get to choose the software, the algorithm, and the machine it runs on. You can pick a simple, fast algorithm, or a computationally intense one that takes longer to run. When you let the camera do it, you don't get to make such decisions: the camera will use whatever is built in. The restriction is that the camera designer didn't have the freedom to choose a computationally intense program that might take tens of seconds to run for each shots.

I've compared three upscaling methods:

  1. In-camera. I've used CIZ, which is a Sony term; Panasonic calls the same thing iZoom. This is a digital zoom technique limited to 2x upscaling, and is claimed to use some sort of advanced, proprietary algorithm that produces superior images compared to conventional digital zoom. Obviously, any JPEG Sony shooter has easy access to this method, but it's not am option for raw shooters.
  2. Bicubic interpolation. This is a popular, widely available method, included, often as the default, in most photo editing and viewing programs (some free). So, anyone who post-processes images has access to this method. It's based on fairly advanced mathematics, but as a user, you don't need to understand how it works, and there are no parameters to set. So it's free and easy to use for anyone who post-processes, whether they shoot JPEG or raw.
  3. The third method is new, and much less well known. It was recommended by David, who's very fussy about image quality, so I decided to give it a try. It's a stand-alone program, called Topaz AI Gigapixel. This is a single function $100 program, so it's relatively expensive, and few people already own it. It also benefits from a powerful computer with a strong graphics card (which my machine has). So you need to be a fairly dedicated, quality-obsessed, well-heeled post-processor to use it (ie, someone like David).

This is the scene I shot in RAW+ Extra Fine JPEG. It's not challenging for JPEGs, as it doesn't have a high dynamic range, and didn't need a high ISO. I couldn't get closer, as there's a fast slowing river in the way:

OOC Extra-fine JPEG, optical zoom only (ie, 200mm equiv)

Processed from RAW, using DxO PhotoLab 2. I used this image as the basis for post-process upscaling.

Now let's imgine that we're obsessively interested in the area around the EAT sign. Let's look at a 100% 1000x750 crop of the OOC JPEG:

This is just a crop of the original full-size JPEG. It's equivalent to a crop of a smart zoom image

And now the same with the RAW:

100% crop of RAW processed image

Now we get to the contentious part:

  • Is it worth upscaling (other than for large, high resolution printing)?
  • If so, which method to use?

Let's start with Elliott's favourite, CIZ, then the two post-processing methods:

So, let me ask you?

  1. For on-screen viewing, was the upscaling worth it?
  2. Please rank the three upscaling methods for image quality
  3. Does the worst upscaling method produce better or worse onscreen quality than a simple crop?

I have my own analysis of the relative image quality, but I'd like to hear from others.

 Digital Nigel's gear list:Digital Nigel's gear list
Panasonic FZ1000 Canon PowerShot G7 X Nikon Coolpix P900 Panasonic ZS100 Sony RX10 III +15 more
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