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Previews Best Practice (or why Auto Preview makes no sense)

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Gray Jay

New Member
Premium Classic Member
Joined
Mar 14, 2024
Messages
4
Location
New Jersey, U.S.A.
Lightroom Experience
Advanced
Lightroom Version
Classic
Lightroom Version Number
13.2
Operating System
  1. macOS 14 Sonoma
Hi, this is my first post, I'm glad to have a place to answer my burning questions in my pursuit of mastering Lightroom. :D After reading everything I could about standard preview sizes in The Missing FAQ,I still have some questions.

I recently switched to a new Mac Studio and simply took my external SSD with my LR library and other external HD with all my photos on it and plugged it into the new computer. I don't know if it is because it carried over the Catalog Settings preferences, but the Standard Preview Size is set to Auto (5120px). My old computer was a 5K monitor, my new one is 4K. I'm wondering why the auto setting isn't 3840px. That isn't even a choice in the dropdown menu. The next highest is 2880px.

From what I've read having my standard previews set to 5120px doesn't make sense since my monitor's resolution is only 3840x2160. I'm also not using the entire width of my monitor to view the images since the left and right panels are open. I don't know how many horizontal pixels the panels take up. So I think it would make sense to drop the standard previews down to 2880px. Although that's lower than my monitor's horizontal resolution, would that seem to be the best practice?

The other thing is, should the standard previews be set to what the monitor is capable of or what the resolution it is set to in the preferences? I have my monitor set to 2560x1440; having it set to the full 3840x2160 resolution makes everything on the screen impossibly small. Even with my old iMac 5K display was set to the same 2560x1440. So was there ever a need to have the standard previews set to 5120px? It seems like to me that computer should have been set to 2880px too. Otherwise I'm just wasting space for resolution I'm not even using.

On top of that, it sounds like if the 1:1 previews are close to the size of the standard preview, it will use the 1:1 previews as the standard previews. So that means it is always holding 1:1 previews even if you say to automatically discard 1:1 previews after one week. For example, if I have 1,000 raw photos at 5184px wide I will have 1,000 1:1 previews at 5184px and those will also be used as the standard previews. Since they are the standard previews, they will never be automatically deleted. In the scenario where I choose 2880px standard previews, I would have 1,000 photos at 2880px plus the 1:1 previews at 5184px. Those 1:1 previews will be automatically deleted after one week but the standard size (2880px) previews will remain. The latter scenario seems like it would save a lot more hard drive space. Is this logic correct or is there something I'm missing?

All of this seems to be pointing to using 2880px standard previews. I really see no advantage of using 5120px standard previews even if you have a 5K monitor. The main reason I'm doubting all this is why would Adobe make 5120px the auto setting. There must be a logical reason. I'd like to know what others think about this.

Thanks for your time,
Jay
 

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My M2 Ultra Apple Studio and 4 K monitor have the Auto setting at 6016 px. I don't know how it is arrived at, but guessing this is roughly 80% of my maximum image long edge and might be based upon the GPU cores available. On import, I only generate minimal Previews and no smart previews at all, letting the LrC app generate 1:1 previews only when it needs them. Because I do not automatically generate standard previews, this 6016px number does not bother me
 
The explanation is as follows. If you use a high resolution monitor like a 4K or 5K monitor, then you will normally set the resolution in MacOS System Settings to a lower one, because the menus and other interface items will be tiny if you don’t. So let’s assume that you set it to 2560 pixels wide. If MacOS would simply use this resolution, then all applications would draw their interface items for a monitor of 2560 pixels wide. The hardware resolution of you monitor obviously did not change however, so MacOS would have to upscale this to 3840 pixels and that means everything on screen would look soft. So what MacOS does is tell the apps that the resolution is 2 times 2560 pixels, so they will render their interface at 5120 pixels wide. Now MacOS can downscale this to 3840 pixels, which keeps it sharp.

Ideally, Lightroom would only obey this MacOS resolution trick for interface items, and ignore it for the image display, but unfortunately it does not ignore it. That is why it renders 5120 pixels wide previews if set to ‘Auto’.
 
The explanation is as follows. If you use a high resolution monitor like a 4K or 5K monitor, then you will normally set the resolution in MacOS System Settings to a lower one, because the menus and other interface items will be tiny if you don’t. So let’s assume that you set it to 2560 pixels wide. If MacOS would simply use this resolution, then all applications would draw their interface items for a monitor of 2560 pixels wide. The hardware resolution of you monitor obviously did not change however, so MacOS would have to upscale this to 3840 pixels and that means everything on screen would look soft. So what MacOS does is tell the apps that the resolution is 2 times 2560 pixels, so they will render their interface at 5120 pixels wide. Now MacOS can downscale this to 3840 pixels, which keeps it sharp.

Ideally, Lightroom would only obey this MacOS resolution trick for interface items, and ignore it for the image display, but unfortunately it does not ignore it. That is why it renders 5120 pixels wide previews if set to ‘Auto’.

That reasoning does not explain my 32” 3840px monitor. My MacOS display is set for 3840 on that monitor. According to your math, “Auto” should read 7680px not the 6016px that my catalog settings displays.

I generate only minimal previews on import. When does LrC generate “Standard” Previews?
 
I generate only minimal previews on import. When does LrC generate “Standard” Previews?
If a Standard Preview doesn't exist, it will be generated automatically whenever the image appears on screen (in the Grid or Filmstrip).
 
OK, I figured out where the 6016px is coming from on my Catalog settings. I have two 4K monitors, One a 32" set for a resolution of 3840X2160 The other is a 27" 4K monitor max resolution of 3840X2160 but set up as 3008X1692. So 3008 X 2=6016.
 
Interesting point re multi monitor scenario.

I have a 32 inch AdobeRGB capable monitor, which is ample for 99.9% of my needs.

However, I was having trouble sometimes where my System would boot, but my monitor remained completely blank/black. I know the PC has booted successfully, because I can log into and operate my PC via remote control software ( from iPhone, iPad, Mac or alternative Win pcs).

To trouble shoot…. I purchased a 15 inch monitor and using a hdmi port to the same graphics card as my main monitor.

The basic idea… if my main monitor does not boot correctly…. I can check if my second monitor is working, thus isolating the root cause to my 32 display.


As I now leave my second monitor active all the time… I need to check if this is changing my std preview settings.

BTW.
With the second screen connected the instance of booting to a black/ blank monitor has disappeared, but I cannot be sure if problem eliminated.

The old problem has been replaced by a new ‘feature’. Very very occasionally both screens go completely blank/ black for a few seconds. While this is unpleasant, it is 1000% better than dealing with a totally dumb machine… which requires shutdown, followed by unplugging power , then reboot to get back working.
 
The explanation is as follows. If you use a high resolution monitor like a 4K or 5K monitor, then you will normally set the resolution in MacOS System Settings to a lower one, because the menus and other interface items will be tiny if you don’t. So let’s assume that you set it to 2560 pixels wide. If MacOS would simply use this resolution, then all applications would draw their interface items for a monitor of 2560 pixels wide. The hardware resolution of you monitor obviously did not change however, so MacOS would have to upscale this to 3840 pixels and that means everything on screen would look soft. So what MacOS does is tell the apps that the resolution is 2 times 2560 pixels, so they will render their interface at 5120 pixels wide. Now MacOS can downscale this to 3840 pixels, which keeps it sharp.

Ideally, Lightroom would only obey this MacOS resolution trick for interface items, and ignore it for the image display, but unfortunately it does not ignore it. That is why it renders 5120 pixels wide previews if set to ‘Auto’.
OK, so that explains what I thought were weird results from an experiment I did. I tried to test how much space a 5120x5120 blank white image I created in Photoshop took up vs. a 2880x2880 image. I imported the image into LR and viewed them at 100% in loupe view. The 2880px image was much smaller than the width of my screen (see attached screenshot). The 5120px image pretty much was the entire width of my monitor. I cropped one to 3840px and it happened (probably by coincidence) to fit the preview window with both side panels open.

So I guess I will stick with the Auto (5120px) setting.
 

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OK, so that explains what I thought were weird results from an experiment I did. I tried to test how much space a 5120x5120 blank white image I created in Photoshop took up vs. a 2880x2880 image. I imported the image into LR and viewed them at 100% in loupe view. The 2880px image was much smaller than the width of my screen (see attached screenshot). The 5120px image pretty much was the entire width of my monitor. I cropped one to 3840px and it happened (probably by coincidence) to fit the preview window with both side panels open.
Yes, this is a nuisance and fundamentally wrong. I have been in a fight with Adobe over this for many years, because it also means that a “100%” view in Photoshop or Lightroom is not really 100% (one screen pixel is one image pixel) unless your monitor setting is either the native setting or 50% of the native setting (so 1920 x 1080 pixels for a 4K monitor). In all other cases you think that you are viewing the image at 100%, but in reality you are still seeing a resampled image. Unfortunately, Adobe is unwilling (or unable) to solve this.
 
it also means that a “100%” view in Photoshop or Lightroom is not really 100% (one screen pixel is one image pixel) unless your monitor setting is either the native setting or 50% of the native setting (so 1920 x 1080 pixels for a 4K monitor). In all other cases you think that you are viewing the image at 100%, but in reality you are still seeing a resampled image.
Yeah, I always had a suspicion that something was up with the 100% view. If I open an image in Lightroom at 100%, it's always smaller than when I open it in Preview and select "Actual Size." Maybe that's why I find it easier to evaluate sharpness at 200% rather than 100%. At least that was the case with my old 5K monitor.
 
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