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I use Photoshop to create a panorama from 3-7 photos. Then I export it back into Lightroom. My RAW files are either DNGs or JPEGS when I import into Photoshop. When exported back to Lightroom, when I darken the skies through the gradient filter, the sky will show pixels. Why? How can I avoid this besides making the changes to each photo in Lightroom before exporting to create a panorama.

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    \$\begingroup\$ What is the bitdepth of the photos when you use the gradient filter? Because low bit-depth images will quickly show noise or banding during post-processing, especially during darkening. \$\endgroup\$
    – TFuto
    Oct 7, 2014 at 15:44
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    \$\begingroup\$ Could you post an example image? Increasing contrast and reducing brightness will also make dust spots more noticeable. \$\endgroup\$
    – Michael C
    Oct 7, 2014 at 22:27
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    \$\begingroup\$ Can you provide any photos as examples? That would make identification of the problem a lot easier. \$\endgroup\$
    – Hugo
    Oct 9, 2014 at 6:00
  • \$\begingroup\$ Can you clarify on what you mean by "my RAW files are either DNGs or JPEGS when I import into Photoshop"? RAW files are neither. :) Do you mean you bring JPEGs into Photoshop to stitch a JPEG that you import into Lr? JPEGs inherently have less latitude for post-process manipulating because of JPEG compression discarding color data. Keeping everything as DNG or TIFFs until final export from Lr is probably the best way to go to avoid color halos. \$\endgroup\$
    – inkista
    Nov 8, 2014 at 20:10
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    \$\begingroup\$ What do you mean by shows pixels? Hot pixels? Noise? Jaggies? The entire digital image is made of pixels! \$\endgroup\$
    – Itai
    Nov 8, 2014 at 21:32

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Typically the reason is that by darkening the sky you're basically mapping a certain range (say, 10 levels) in a more extended range (let's say twice as much, 20). Therefore you're actually enhancing the tone difference between adjacent pixels.

An extreme example of this is when you stretch the range so much that you start to see the quantization error: it means that two pixels that were just across the border between two tones (therefore impossible to distinguish) become visibly different.

You can partly correct for this by smoothing the image, even better if with selective smoothing to preserve detail. But the best way is of course not to have to stretch the exposure range. You can use exposure blending or HDR to capture higher dynamic range, and of course prefer RAW over JPEG as it has a wider dynamic range and no compression artifacts.

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