P: Library Preview Zoom Interpolation Changed

[Todd Shaner]

Lightroom Classic  9.3 Library Preview Zoom interpolation type has been changed to nearest neighbor. Nearest neighbor interpolation uses a simpler and faster algorithm that can create "jaggies" and other artifacts in the image. Presumably this was done to reduce preview building time, but don't know. I checked LR Classic 8.4 and Camera Raw 12.3 (most current) and they
both appear to use bicubic or bilinear interpolation, which does not exhibit the artifacts seen with nearest neighbor interpolation.

What this means is that the ALL of the Library Zoom view settings less than 1:1 may exhibit artifacts with certain image files that appear as edge "jaggies' or moire' patterns. This makes them less useful for evaluating the image detail at Zoom settings of resized export and print output. Here are examples using Lightroom Classic 9.3 showing PS Image Size panel with 33.33% (1:3 Zoom) image resizing using Nearest Neighbor (top screenshot) and Bicubic Sharper (bottom screenshot) Resample algorithms.

Observe the moire' pattern artifacts in the black fence at the center of the below picture when using nearest neighbor resizing. The bicubic sharper resizing in the 2nd screenshot does not exhibit these artifacts. I also checked PS Image Size Bilinear Resample and it does not exhibit the artifacts. LR Classic 9.3 Develop module doesn't exhibit these artifacts indicating it may  have been changed to bilinear Zoom resizing.
 
Summary
Adobe should at the very least use bilinear Zoom resizing in the Library module or return to the original bicubic resample interpolation, which provides the most accurate rendering.

(right-click on images to see full-size)

[johnrellis]

If you build 1:1 previews, do you still see the jaggies/moire effects at less than 1:1 zoom?

[Todd Shaner]

Yes, I still see the artifacts whether zooming to 1:1 or discarding and rebuilding 1:1 previews and then viewing at a lower Zoom setting (1:2, 1:3, 1:4, etc.). In my example screenshots I used 1:3 Zoom in LR and compared it to PS Image Size panel using 33.33% and Nearest Neighbor Resample. The artifacts look identical in both so it's clear Adobe changed the Library preview  interpolation from bicubic or bilinear to nearest neighbor since LR Classic 8.4 doesn't exhibit the artifacts.

[Todd Shaner]

UPDATE: The issue is not observed when 'Use Graphics Processor' set to Off and LR is closed and restarted.

I updated my Nvidia Quadro P2000 graphics drivers to the latest July 16, 2020 version 451.77, restarted my system and checked again. The issue remains using the latest driver so Adobe has made changes that are not compatible with the Nvidia drivers. Somewhere in the display pipeline the 1:3 Zoom and smaller Library Preview is being scaled using nearest neighbor interpolation. As I mentioned the Develop module preview does not exhibit this issue so it's being applied at the app level and not the display pipeline.

You can download the Canon 5D MKII CR2 I used in the above screenshots to see if your system is affected. Zoom to 1:1 view, wait for the preview to build, and then set the Zoom view to 1:3. Look at the black fence in the center of the picture. If it looks like the top image in the below screenshot your system is affected as well.

https://www.dropbox.com/s/5moo207u90gvjbz/IMG_0154.CR2?dl=0

Lightroom Classic 9.3 Library Module 1:3 Zoom View

(Top GPU Enabled, Bottom GPU Disabled and LR Restarted)

[johnrellis]

On my LR 9.3 / Mac OS 10.15.5 / Macbook Pro 2019 / Radeon Pro Vega 20 4 GB, with the GPU enabled, when I zoom from 1:1 to 1:3, I see the moiré patterns fleetingly. Then as I pan the photo at 1:3, the moiré appears only when I'm holding down the mouse. See this screen recording:
https://www.dropbox.com/s/4ntc7pdx0s00gd5/nearest-neighbor.2020.07.28.mov?dl=0

So maybe in normal operation, whenever LR changes the zoom or pans, it uses nearest neighbor to display an initial image quickly. Then after the initial display of a zoom, or after the pan stops, it redisplays with the slower bicubic.  And perhaps that redisplay is getting stuck or not working on your system with the GPU enabled.

[Todd Shaner]

Then as I pan the photo at 1:3, the moiré appears only when I'm holding down the mouse.

I noticed the same behavior when I set 'Use Graphics Processor' to Off. It makes sense to use the faster and less accurate nearest neighbor interpolation since the screen needs to be update real-time as you move the image in the window. I'm on Windows 10 so perhaps it's not happening with Mac OS X systems. If something is causing it to get "stuck" in the nearest neighbor panning mode it should be easy for Adobe to fix it.

[johnrellis]

Unfortunately, my Windows configuration is a virtual machine running on Mac, which doesn't support use of the GPU, so I can't test this on Windows.

[Todd Shaner]

One other thing I noticed is that when setting 'Use Graphics Processor' to Off I also had to open and close LR. However, you can see the impact to editing performance without restarting LR. Unchecking just 'Use GPU for image processing' does not stop the artifacting even with a LR restart. So it's the 'Use GPU for Display' setting that's loading something on LR startup that's causing the issue.

[Just Shoot Me]

Did you mean 3:1 Zoom and not 1:3?

I don't see what you are showing. But I'm using a 9 year old computer with a 9+ year old NVidia video card. No more updates for it.

[Just Shoot Me]

OK with GPU on and 1:3 zoom I see the effect on the fence.
With the GPU off I don't.
Driver version 388.13. OLD!!!!

[Todd Shaner]

Thank you *Just Shot Me. What OS LR Classic version are you using? *John R. Ellis does not see the issue on his Mac Pro with OS 10.15.5.

Driver version 388.13. OLD!!!!

I'm using an Nvidia Quadro P2000 GPU with the latest July 16, 2020 driver version 451.77. So it appears to be unrelated to the GPU Model or driver version.

[Just Shoot Me]

Win 10 1909 9.3 LrC.
Vid card is a GeForce GTS 450

[thedigitaldog]

It doesn't matter what interpolation algorithm is used for PREVIEWING in Library. It's not accurate and never was. It's built for speed, not precision of viewing the data.

Previews for color, tone and sharpness must be viewed in Develop. The preview architecture, the data used, the color space for previewing is totally different and one must zoom to 1:1 for a proper preview of that data (like sharpening). 

For output (rendering of data) using Export or Open in Photoshop etc, LR uses a unique Adaptive Bicubic algorithm. It's not like anything in Photoshop, it's actually visually better! 

Adobe Photoshop Lightroom resampling is a hybrid Bicubic algorithm that interpolates between Bicubic and Bicubic Smoother for upsampling and Bicubic and Bicubic Sharper for downsampling. Lightroom and ACR uses a adaptive bicubic algorithm: the algorithm parameters are chosen automatically based on the relationship between the original image size and the final image size. These parameters were determined empirically by doing lots of experiments with photos being resampled to common output sizes, such as web-sized images (800 to 1000pixels on the longer dimension), small prints, and big prints. I can see slight improvement over the same resizing using various Photoshop algorithms. 

[Todd Shaner]

It doesn't matter what interpolation algorithm is used for PREVIEWING in Library. It's not accurate and never was. It's built for speed, not precision of viewing the data.

Andrew the topic of this report is that something has "changed" in the way LR Classic builds it's previews.  Whether or not it's accurate is not the issue. I'm just requesting to have it work the same as previous with the GPU enabled as in the bottom screenshot below.

In LR 5.7.1 and earlier versions the previews did NOT exhibit jaggies and moire' artifacts at 1:3 Zoom and smaller in the Library module. It's only present in LR 6 and later versions on Windows 10 systems when the GPU Is enabled as below. So clearly there's a problem and that's what I'm reporting. Something in the GPU display path rendering is not working properly.

If you have access to a Windows 10 system try it for yourself and report back here with your results. Thank you.

Lightroom 9.3 on Windows 10
Top GPU Enabled: Moire' visible in the black fence
Bottom GPU Set to Off and LR Restarted: No artifacts visible.

[thedigitaldog]

Andrew the topic of this report is that something has "changed" in the way LR Classic builds it's previews.  Whether or not it's accurate is not the issue. 

Sure it does. If something is new that greatly speeds up Library, while the new and old are both inaccurate in previewing the actual data, it doesn't matter (at least to me) there was a change. 

There are differing ways to build previews in LR; they may not appear identically as such outside Develop. Nothing new here. 

No, I have no access to a Windows machine. 

[thedigitaldog]

In LR 5.7.1 and earlier versions the previews did NOT exhibit jaggies and moire' artifacts at 1:3 Zoom and smaller in the Library module. It's only present in LR 6 and later versions on Windows 10 systems when the GPU Is enabled as below. 

Well lots of functionality is being moved TO the GPU for speed and that's going to continue. Meaning that:

1. Such a change should not be assumed to be a change in interpolation algorithms for previews. Might be but that you don't see this with GPU off indicates point 2. 
2. GPU is problematic for many users (sorry to say and according to Adobe, mostly on Windows), there's a reason why you have the ability to turn OFF GPU. 

[Todd Shaner]

It's my understanding that the Lightroom .lrprev preview files contain an image pyramid with all of the Zoom Views from 1:1 through 1:16 and a thumbnail image. These are all prebuilt during Preview Building and only need to be interpolated when using Fit or Fill Zoom View setting, which uses a second interpolation to resize the image onscreen.

Interestingly the Fit and Fill screen previews don't exhibit the artifacts with GPU On or Off, even though they do need to be re-interpolated. When viewing image files using 1:16 through 1:1 Zoom View settings no further interpolation is required, but they exhibit nearest neighbor interpolation artifacts. Clearly something is wrong and it shouldn't be difficult to fix.
BTW- I'm a system design engineer with 50 years of experience in mainframe computer, minicomputer, and embedded Intel systems experience. I helped design the computer systems used in the Space Shuttle simulator in Houston, TX and in the Bloomberg Trading facility in New York City. I've also been using Photoshop since 1994.
Stepping down off of soapbox....

[thedigitaldog]

Unless something has changed recently.....

1:1 previews are not used in Develop but in Library for quick zooming. 
Standard size previews are also used in Library but not Develop (very briefly then not; that's where the cache comes in).
The size of Standard size previews varies based on preferences. It is indeed a pyramid like preview structure of JPEGs in Adobe RGB (1998). But 1:1 are full sized JPEGs in the same color space. Then there are the newer Smart Previews which are partially processed raw data, always at a fixed size regardless of the original raw.

The preview quality setting defines amount of compression applied to the JPEG files making up the preview pyramid for each image. Typically, you will
have 5 to 7 individual previews of different pixel dimensions making up this
pyramid. When you create a Virtual Copy another pyramid is created, and so
on. 

[Todd Shaner]

1:1 previews are not used in Develop but in Library for quick zooming.

Correct, and the Develop module needs to build its previews real-time to display the effect of editing changes. Because of this it uses the faster and less accurate bilinear interpolation to prevent control lag.

The primary purpose of the Library Preview database is to provide more accurate preview rendering of the currently applied Develop settings. If this were not the case Adobe could have simply used bilinear interpolation for Zoom View and only build a thumbnail database like Bridge for the Grid view.

I tested this on two Windows 10 systems with LR Classic 9.3 and they both exhibit the issue. Also two other users have confirmed they see it on their Windows 10 systems. Having the ability to view and compare image files at less than 1:1 Zoom View is very useful with higher megapixel (50+) images to determine what they will look like when resized for screen viewing or print. It's also useful with high ISO image files to evaluate the effect of Sharpening and Noise Reduction at reduced image sizes that are close to the pyramid Zoom View settings. Currently the Zoom settings 1:16 through 1:3 are very inaccurate.

Here's the same raw file I used in the above screenshots shot at ISO 100 with no visible noise in the image. I set Sharpening Amount to 100 in the below screenshots showing the Develop and Library module previews at 1:3 Zoom View. Scary looking and useless for any purpose!
(click on image to see full-size)

[Todd Shaner]

Another user with the the same issue here:

https://feedback.photoshop.com/photoshop_family/topics/lrc-9-3-library-mode-does-not-reflect-all-dev...

[thedigitaldog]

The same misunderstanding of the differences in previews in the modules.

[thedigitaldog]

Lightroom Classic  9.3 Library Preview Zoom interpolation type has been changed to nearest neighbor.

Since this forum post has been referenced in a newer one started today, I think it's important to point out, that may not at all be true.

Something is going on here, for some users, perhaps only on Windows, perhaps not, but the statement above hasn't been vetted! When enough actual hard data is provided directly from Adobe, it is possible this can be put to bed. But at this point, it's not a known-known-trust by verify. 

https://feedback.photoshop.com/conversations/lightroom-classic/horrible-noise-in-library-module/5f91...

[Rikk Flohr: Photography]

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