When to Upscale?

[henryg]

This is obviously not a question limited to APhoto, but after editing and (substantial) cropping of jpg images, is there any point in upscaling to something approaching the original resolution before resaving as a jpg?

[MEB]

Hi @henryg,
Welcome to Affinity Forums
No, there's no point in upscaling unless you really need a bigger image/output. Any downscaling or upscaling always affects image quality negatively because you are either interpolating or removing pixels from the original image which affects its sharpness/definition. If you really have to upscale use a proper resampling algorithm (depends on the type of image) to get a better result.

[Albo]

I might need to upscale some images. What would be the proper algorythm for PNG images?

[Alfred]

The appropriate algorithm doesn’t really depend on the file format (e.g. JPEG, PNG, or TIFF). Generally speaking, bilinear or bicubic resampling is adequate for downscaling but Lanczos3 (separable or non-separable) is better for upscaling.

When choosing a file format for export, what’s important is the type of image; i.e. whether it’s a photograph or a graphic comprising large areas of solid colour, with or without text. Even a small amount of JPEG compression will introduce artefacts at the boundary between blocks of solid colour, an effect which is especially noticeable around the edges of any text in the image.

[Albo]

Thank you.

Mostly pictures of stamps. Some are simple graphics while others are much more complex illustrations.
I will try with the Lanczos3 and compare.

 

[RichardMH]

Its not cheap but Topaz Gigapixel AI might be worth a look if you're not happy with AP. There is a free trial version.

[Albo]

Thanks Richard,

I tried with Lanczos3 and it works very well. I am upscaling but not to an exagerated size.

 

[henryg]

Any guidance on when to use Lanczos3 separable or non-separable? Googling didn't come up with anything much.

[Old Bruce]

3 minutes ago, henryg said:

Any guidance on when to use Lanczos3 separable or non-separable? Googling didn't come up with anything much.

21 hours ago, Alfred said:

The appropriate algorithm doesn’t really depend on the file format (e.g. JPEG, PNG, or TIFF). Generally speaking, bilinear or bicubic resampling is adequate for downscaling but Lanczos3 (separable or non-separable) is better for upscaling.

Upscaling means enlarging.

[carl123]

11 hours ago, henryg said:

Any guidance on when to use Lanczos3 separable or non-separable? Googling didn't come up with anything much.