Is it me or is the Lightroom's zoomed out preview inaccurate in displaying noise and color?

Question

I'm having some trouble with the Lightroom viewer (In develop mode) when zoomed out. Look at this picture:

See how the sky seems to have a lot of chroma noise

Now check the zoomed in version (Of the sky part)

I can't see any (significant) chroma noise here!

Finally, check this side by side comparison: Lightroom (RAW original file) and Windows image viewer (Exported JPG, 100 quality) (Click here for the full size version)

The windows image viewer shows a much better sky, without all the "blotches" of color and strong noise that the LR version shows. Do I have something wrongly configured? Do you suffer the same issue?

Answer

I don't use Lightroom but I regularly use Adobe Camera Raw which is pretty much the same thing but built into Photoshop, and have observed the same effect.

By default ACR applies chroma noise reduction to the raw image. The noise reduction only seems to be applied in the preview when you zoom in (perhaps Adobe figured the noise wouldn't be visible in the zoomed out view due to resampling), so what you're seeing in the zoomed out version is the actual noise level, and what you're seeing zoomed in is what it looks like after Lightroom has smoothed the noise.

You could confirm this by turning off noise reduction in Lightroom and seeing if you get the same result zoomed in as zoomed out.

As soon as you export to JPEG the noise reduction is applied to the whole image, which is why you don't see it in the Windows Photo Viewer.

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