Monday, August 18, 2008

Resize artefacts

I was reminded of this by a recent comment from Dorin. I have commented on this before. The resize algorithm used in Lightroom and ACR has a major problem on high contrast edges. Often you will see ringing artefacts. Here is an example of this problem using the truck image from before. I blew the images up 400% in Photoshop using nearest neighbor scaling to show you the ringing more clearly. The photoshop image has some jpeg compression artefacts that are not real. I forgot to scale to 400% before saving it. Just hover your mouse over the image to see the problem (first time it might be slow to show up).

As you can see, the LR scaling algorithm causes ringing artefacts on hard contrast edges. In this case it caused the appearence of a whole extra white band that is obvious even in the not scaled up image. This is WITHOUT any output sharpening applied. Applying sharpening makes this even worse as you can see in the truck image below. You clearly notice this in the full-size image when you're sensitized to them. Look for example at the roof and at the branches. I can often recognize images exported from Lightroom because of this defect. It's especially clear in silhouette type images, such as people against sunsets, or actual sunsets. Look in the black area here for example. I hope the Lightroom engineers will at some point tackle this problem as it has been known since the first LR release that this is an issue. Note also that this also happens when all you do is crop your image and do not scale upon output!

1 comment:

  1. Dorin Nicolaescu-MusteaţăAugust 21, 2008 at 8:26 AM

    After the color problem was solved, this and high ISO rendering are my biggest priorities for future updates.

    Please, no Soft proofing, no books, no flexible print layout until these are solved. (OK, at least resizing - it should be easy).

    For me, Lightroom as it is now, is 99.9% solution for my workflow. It's got everything I really need. Just, please, correct the problems before adding new features.