Lightroom artefacts even show up when cropping

I don't know what causes the artefacts I talked about earlier. I do know they show up when you resize images on export. They also show up if all you do is crop your image. I have generated an example of this, again using the car image from before. I once exported the image uncropped from Lightroom to sRGB tiff, and I cropped it and again exported it. I took the two files into Photoshop, scaled them both to 200% using nearest neighbor scaling and aligned them to each other using the image align built in. Here is the result again using the mouseover trick. The default shows the image that was not cropped in Lightroom. I also include a substracted image that shows just the difference between the two calculated using apply image. The images can take a while to load after you hover so be patient. The change will be VERY obvious.


Not cropped in Lightroom
Cropped in Lightroom
Difference image


You see that is pretty bad. You see it is not just an extra halo that gets created, but also a sort of combing effect arises. Again Lightroom did not scale upon output. This was just the result of cropping. You can see these artefacts immediately in the Develop module in Lightroom when you just cropped.

P.S. I am not the first to point out this problem. Many people have done so before me (example link). I hope this will soon get fixed. You need light objects on dark backgrounds to see these effects (or the inverse). You see that even in pretty standard sort of images these problems can show up. If your image is not so sharp to start with this (the crop-induced artefact) will probably not be an issue. This was shot with a very sharp prime lens that outresolves the D300. However the resizing artefacts will show up even for less sharp images.

LR 2.0 review

Dave Girard from ars technica just posted a review of LR 2.0. I have always enjoyed his reviews and this is bound to not be an exception. If you're still on the fence on whether to get LR 2, go read this and you'll get lots of objective info.

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!

On output sharpening

Lightroom 2.0 includes new output sharpening facilities in the export dialog, the print module and the web output module. These are extremely useful. The functionality is to correct for softness induced by the scaling for output and for the softness of the output medium such as a screen or a printing process. Here I'll talk about the use for output images for the web, email, etc. I used the export dialog scaled to 600 points for the long dimension and selected different levels of "screen" sharpening. Here is an example of a waterfall image. See (and buy prints of ;-) )the real image here. You can switch between different output sharpening levels by hovering over the names on top.


unsharpened
low sharpening
standard sharpening
high sharpening


To me, the difference between no sharpening and even just low sharpening is night and day. In the lychen details on the wet rocks for example. You wouldn't notice probably if you just have two images in different contexts, but you would probably thin-slice prefer the slightly sharpened one. The high sharpening is still very good in my opinion and works well for this image.

Here an another example of a cliché truck. This image has lots of sharp detail and you'll see that going to high has a different effect than on the waterfall image.

unsharpened
low sharpening
standard sharpening
high sharpening


Notice the extraordinary amount of extra detail that is pulled out in the hood area by the sharpening. This time, I think high is over the top and the best is probably low or standard. This is quite generally true for images that have man-made structures that have very sharp transitions. In general I have found that using standard gives very good results for most images, but of course this all depends on your taste.

Sunset in Mayflower

Continuation of an older post.

Columbine and waves crashing:

Billowing clouds

Set of images on flickr.