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Let's say I have a photo saved by someone else just found on the web that is 500px wide (therefore I have no control over DPI etc)

If I resize that photo to 1000px and sharpen it a few times, then serve it at 500px wide (but it's still 1000px wide) on my website will the quality still be poor or will it improve to any degree making the process worth while?

I guess my question is, is it worth scaling up images to retina size (but don't match in full scale quality) or just serve the non retina ready image.

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    Hello and wellcome to GD.SE. Perhaps, it depends on how good quality your up scaling algorithm is. It might do a better job than the browser. But realistically speaking, if you must ask, then the answer is no. As you'd know when you have a better algorithm at your disposal, but then your mileage may vary and the benefit is most likely marginal.
    – joojaa
    Apr 11, 2015 at 21:04
  • @joojaa I was simply thinking imagemagick or something, scale it up and sharpen, no proper quality processing algorithm. So, you're right no would be the answer. Thanks for the input, I just wanted to know if should wipe the idea from my head!
    – GoldenGonaz
    Apr 12, 2015 at 9:47
  • Imagemagick has better algorithms, for scaling, at its disposal than what photoshop offers you.
    – joojaa
    Apr 12, 2015 at 10:23

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Yes, you could upscale the images manually and get some improvement. But the question would be: Is it worth it?

Even if you managed to get a semi-noticeable result (which I honestly doubt :/) you would have a very heavy image that looks almost exactly the same as the non-retina. When bandwidth is an issue, do you really want to force users to download a larger version that probably won't make that much of a difference?

As Joojaa mentioned in the comments, the benefits are most likely marginal. I would upload new images only if you can re-create them from scratch, or focus on elements that might not be scalable but could potentially be. Icons, for example.

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An image only has the amount of detail the original contains. While there can be some benefits to upscaling, it’s almost always a net loss — information can’t magically be created from nothing (or nearby pixels).

There are some very smart upscaling algorithms, and I’m sure they will continue to improve, but generally speaking, I’d stick with the biggest native size you have.

If you absolutely must upscale an image with the aim of creating the impression of more detail, I’d probably do the something like this:

  • Upscale using Nearest Neighbour to an exact multiple (2×, 3×, 4× the dimensions).
  • Clone the original image and upscale to an exact multiple (2×, 3×, 4× the dimensions) using the best interpolation method you have available. For Photoshop, that probably means using Bicubic (Automatic).
  • Place the Bicubic version as a layer on top of the Nearest Neighbour version.
  • Use a mask for the Bicubic version. Set the mask to hide everything, then airbrush in the edge details where being blurry is preferable to being pixelated.
  • Add a tiny bit of noise to the entire thing. Not much… just enough to add the impression of detail.

Honestly though, in your case I’d either look for a better quality original, or leave it alone.

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