Thank you for the pointer to this info. This is VERY helpful for understanding what is going on in the background. A couple things to note here: 1. Screen size is NOT the same thing as optimal preview size. For instance, if you are using a 27 iMac, your resolution is: 2560-x-1440. So what size preview is "the best?". You would think that since the long edge of the screen resolution is 2560, that a preview with 2560 resolution (if there were such a thing) would be the best. This might lead a user to think that they only have the option of using 1:1 previews to get the optimal experience on a 27 iMac. This isn't the case though. The limiting side in this case is 1440, your image will never be "taller" than 1440, no matter if it a portrait or a landscape. My camera (7d) has a 2:3 resolution...so the widest image from my 7d that I can possibly see on the screen is 2160. 1440 / 2 * 3 = 2160. When you take into account that the Lightroom application takes up some of the pixels on the top and bottom of the screen, you can then see that the 2048 standard preview size is sufficient. You shouldn't have to do 1:1 previews for LR to be optimal. 2. But there is more to the story here. It might be that 2048 preview size is less than optimal, because it is actually too big. It takes some time to load the preview from the disk, and if you are working with a big preview, it's going to take longer to grab from the disk. Modern computers are pretty good at up-sampling images. On the other hand, it is going to a little time for the processor to resize the images, because the LR interface isn't "fixed" in size, and the user can change things around. So it is really random what size the preview is actually going to be in the end. I did some tests looking at various size/compression previews, and I couldn't visually tell a difference (on the 27in iMac) between 2048 and 1680. It seemed to me that the 2048 was SLOWER rendering though, which is contrary to what you would think, since that would be the "right" size for the monitor. So in the end I just wasn't sure which was best, because I couldn't tell which previews (on the disk) I was actually looking at. One solution to some of these problems would be to have a SQUARE shaped reviewing interface that is fixed according to the monitor size. This would only be for the Filmstrip view (or some new mode), not the develop where you absolutely need to see the whole screen, and you are rendering 1:1 anyway. So the "portal" that images show up in would have the same length and width, and this would be the exact size of the standard size preview. So the image would not have to be resized after it is grabbed from the disk. This has the added perceptual benefit of not being "jumpy" as the user moves though images with different aspect ratios. Finally, ideally the compression ratio would be automatically sensibly set based on user testing, so there isn't a situation where the previews are "heavier" than they should be. This would make things super-fast. r ps the preview pyramid concept is pretty cool. It would be neat to see that info in the UI somehow.
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