I upgraded to Lightroom 2.5 yesterday (9/20/09), which includes an upgrade to Adobe Camera Raw 5.5. I started to see a purple artifact appear in highlights after making edits. (I haven't yet investigated enough to identify which editing tool triggers the artifact, or perhaps all of them.) Even when I revert History to the original Import step the purple artifact remains visible on screen.
I'm working with ORF files from the Olympus E-510. ORF is Olympus' RAW format.
When I use the 'Edit in' command in LR to open the same file in Photoshop CS4 11.0.1, with or without LR edits, the highlights artifact remains. LR instructed me to upgrade ACR to 5.5 in Photoshop, for compatibility with LR 2.5, which I did before opening the first file. When I later opened the same ORF file straight from PS, it contained the highlights artifact.
When I saved a JPG from LR, the artifact remained in the JPG file. Opening the JPG in Apple's Preview shows that the artifact is at the pixel level - it is there without using an Adobe product to view the image. Therefore the bug is not restricted to viewing images, but also to processing and saving images.
To test whether the ORF (RAW) file had been altered by LR, I opened it in LightZone 3.8. The highlights artifact is NOT present in the image processed by LightZone. Therefore the Adobe products did not alter the ORF (RAW) file. Because the artifact is present in two Adobe products that depend on ACR 5.5, the bug is probably in ACR 5.5. Perhaps in the calibration for the E-510?
I suspect the bug in ACR 5.5 is caused by improper normalization of the R, G and B channels at the bright end of the histogram, so that color balance is not retained when one channel is blown.
Crops of the LR/ACR 5.5 JPG image and the LightZone JPG can be seen at:
The same problem, but with different camera model (Sony) has been reported on Lightroom forum Eric Chan (Camera Raw engineer) is looking into it. You can read more at:
Thank you, Ian, the Lightroom problem is indentical to the one I saw in both Lightroom and Photoshop CS4. Following advice in the Lightroom thread I downgraded to ACR 5.4 and Lightroom 2.4, and the problem went away. I'm happy with the older versions so I'll wait patiently for the fix.