gustup wrote:
Sometimes it happens that if I go to Library and I watch the same picture fullscreen it is full of noise and/or pixels. It seems it happens after I work for more than one hour or so, in fact when I start working on Lightroom there are not differences in watching pictures fullscreen in Library or Develop modules.
When you import images LR builds Library previews using your default Develop settings. The images should look very similar in both the Develop and Library modules. Once you start making edits in the Develop module the Library previews are no longer correct and must be updated. If you simply view the edited images in the Library module at less than 1:1 Zoom view they may in fact look different, which is normal. There are two ways you can "update" the Library previews:
Go into the Library module:
1) Click on each image to launch it in 1:1 Zoom view and wait until the 'Loading' icon goes away.
2) Select all of the image files you just edited, go to Library> Previews>, and select 'Build 1:1 Previews> 'Build All.'
Concerning the posted Compare view JPEGs I see only a slight difference in sharpness and no real difference in noise. I agree with Jao vdl's observation and suggestions. You may also want to read my suggestions again concerning using the Library module's Pyramid Zoom View settings 1:8, 1:4, 1:2 and NOT Fit or Fill to get the most accurate preview image inside LR. PS and most other image editors suffer from the same 2nd interpolation issue, so this is not something unique to LR.