P: 100% or 1:1 Zoom

Pixel peeping is the act of viewing photos at 100% (or greater) to assess sharpness, noise, and defects. It's often used in a derogatory way due to the tendency to be obsessive about it. However, as a New Yorker its been my experience that we use it here in a non-derogatory / casual way. Then again, we do that for many words that others would consider "bad" elsewhere, lol.

Ultimately, I mean no ill will by it, but what you described is pixel peeping.

As monitor resolutions increase 1:1 zoom is not just for pixel peepers, but seems a very reasonable criteria for assessing sharpness and noise. It also has advantage of displaying the image at the monitor's native resolution removing whatever rendering tricks are necessary for a responsive full-screen fit view with risk for associated artifacts. Often I think rendered images in Lightroom Classic on my desktop (24" monitors) are soft in screen-fit view, but turn out to be perfectly sharp when viewed at true 1:1, so having the ability to review images at a true 100% magnification is the "only" way to make a proper assessment of the image (or re-phrasing that, at-least only way to make a standardized assessment). Let's not forget when we want to crop images which in my case is very often.

According to your calculations the headline should be:

"In the world of Adobe, 1:1 view is not really defined and moreover is dependent on image file resolution and for example in the case of a 24MP 6000x4000 image will be 68.3% zoom on an 11" iPad Pro and iPhone7, whereas it will be 88.97% on a MacBook Pro 13" and 128% on Apple TV 4k, and maybe something else around 70-75% on a 13" iPad Pro. Occasionally it may even be 200%, but you might need an Apple Pencil if you want to tap into that feature more regularly"! Just kidding around, but that seems to be the present deal with Apple OS based products.

Looking forward to your calcs for the 200% "bug"

Yeah, it'll be interesting to see if the 200% matter is a relative calculation based on the previous zoom (or just a programmatic slip / double-triggering), or actually calculating the 200% correctly. Also interesting to see if I can get the bug to trigger across devices, I only tested the iPad on that. Will check it tomorrow. Also I have an Apple Pencil 2, so I'll check to see if it's easier for me to trigger the bug using it also.

@ "feature request" ... I think the 200% bug is the issue, but can also see how the non-1:1 would be an issue for those whose style / livelihood relies on tack sharp focus. The fact that Photoshop's 100% zoom is incorrect on macOS, this might be an issue that goes back pretty far. I can see the headlines now, "in the world of Adobe you've only been seeing 98% of what you should've" or "1:0.92's the new 1:1"

Kidding of course; everything's probably fine on Windows & Android.

Yeah, I've no interest in where we stand from a "legal" perspective ;-). Would just really like to get to the bottom of this and for the software to behave in an expected and predictable manner.

Also, just wanted to add that this has been a very fruitful discussion so far, and have now been able to highlight that Lightroom CC / Lightroom Mobile CC on Apple OS based HW platforms does not yield anything resembling a true 100% zoom functionality (per our 1:1 pixel relationship definition that is). Moreover the %-age zoom applied is inconsistent from device to device. Then to top it off we have the 200% "bug". Whilst we are clearly experiencing varying mileage in terms of repeatability of this specific behavior (for me it is very easy to induce with Apple Pencil) the 200% issue is a very interesting case because it is the one scenario that is actually providing a whole number relationship giving impression that whatever calculations are being applied have a built-in knowledge of device display resolution? This 200% statement being subject to the more careful measurement methodology you are applying, if you have the time and energy?

Maybe time for moderators of this forum the re-instate my original "feature request" wording in my thread title?

Yes, I believe so @ some devices. I think they simply didn’t test enough iOS devices, or didn’t check it at pixel-level / assumed it was true, or figured it was good enough. In any case it’s not legally problematic, as a relative 1:1 can be mathematically excused.

In regard to Android, the situation is similar to Windows, PPI factored 1:1 calculation is probably standardized.

Very interesting points. I did earlier in this thread speculate if the lack of precise 1:1 zoom with Lightroom Mobile is due to some limitation imposed on the developers due to iOS and or HW complexities. It would make sense if that was case. That said, why then claim it’s a supported feature? On some devices maybe? Wonder if 1:1 zoom works on Android devices for example?

Unfortunately, even if the Adobe Lightroom team knows what 100% zoom should be on Windows, it doesn't inherently mean they know what it should be on Apple OSes. It's a well-discussed issue that Apple uses non-standard measurements of PPI on its various devices. There's no universal way to translate PPI in the Apple world. With Windows it's a literal standard.

When 4k monitors were first released, if a person viewed Windows in the monitor's native resolution the desktop icons were uncomfortably small. That was because Windows at the time did not truly factor PPI into its concept of "resolution". To Windows, it was pretty straight-forward, a pixel was a pixel and nothing more. If an icon was 256px then on a 4k monitor it was 1/4 the size it would have been on a 1080p monitor. -- Now that images / icons adapt to the resolution of the screen, icons can show at the same size regardless of the display's PPI. In turn, the calculations for resolution are now pretty complex. However, in the Windows world it's still straight-forward since there's no hardware that the foundation must be specifically coded to, because Microsoft doesn't typically make the hardware. So instead they need to created a foundation manufacturers adhere to; they create computer standards.

Apple ecosystem is a closed-system. Apple can make its own foundation rules for every single device they release, because they maintain a very tight relationship between hardware and software. This enables them to take full advantage of the hardware, because they can fully adapt the software to the hardware its running on. Developers and hardware manufacturers must then play with the new rules Apple basically creates every time, cause Apple doesn't care so much if they break things for them. Microsoft doesn't have that luxury. -- Consequently, the PPI of "Retina" isn't universal. They push the technology each generation increasing pixel density. So 100% not being true on Apple devices, isn't just an issue on iOS devices. I think the only situation where Apple actually needs to care about the display PPI of outside devices is, for the Apple TV. As that's the only arena where they don't spec / make their own displays / TVs, and instead are playing in an arena where TV standards exist.

In that case the Adobe Lightroom team could have done a 1:1 zoom very easily. However, they didn't even bother, they instead did an exact 50% zoom without error (3000px of the 6000px image showed precisely). Reflecting that they did that specific zoom on purpose. No other Apple devices that I tested came close to being that precise, and that time I measured down to the exact pixel to remove all subjectivity / guessing and estimates. With Apple TV, I'm almost certain they are using pure resolution in their calculations. And I imagine they're using PPI in their calculations of other Apple devices, an approach that would work fine on Windows.

With Windows it's a common base for all devices, with macOS / iOS it's a custom base that changes the rules for each device. I'm sure they could do a true 1:1 zoom on Apple devices, if they abandon PPI, or maintain a device database and test every device.

Just wanted to add that I suppose majority of Lightroom mobile users may never notice or really care about this zoom issue and probably why relatively few have reported it. Point is though adding mobility to a workflow has major benefits even to serious photography enthusiasts and professionals. Lightroom mobile is in my opinion a wonderful addition to my workflow and as it stands is almost where it needs to be, but with a few shortcomings that need to be addressed, amongst these the ability to review images at accurate , defined zoom levels is at the top of the list.

“What does 100% even mean to the Adobe Lightroom team?”

I have asked that exact question myself, however I have checked 1:1 zoom on both D500 and D850 files on my Windows desktop in Lightroom Classic CC and zoom factor does indeed appear to be a correct 100% image file pixel to desktop display pixel relationship. My process for assessing this is approximate by making a rough estimation of how many times I need to fully pan the image along the long axis. E.g., my desktop monitors are 1980 pixels horizontally, full res D850 image is 8288 pixels. At 1:1 zoom I would need to pan across a D850 image 4.19x to cover entire long dimension of image, and this appears to be exactly the case in Lightroom Classic CC. So, I think Adobe team know exactly what 100% zoom is and should be, it’s apparently just not implemented in Lightroom Mobile although it is supposed to be.

Curiously, I decided to precisely measure the 24mp file on the various devices that I have Lightroom CC. -- Opened the original image in Photoshop, displayed the ruler in pixels and placed guidelines at the precise pixel each device zoomed into, then did the math. I saw that aside all of them not being a 1:1 zoom (100%) by screen resolution, there also wasn't any consistency.

1. iPad Pro 11" (2388 x 1668): 58.28%; should be 39.8%
2. iPhone 7 (1334 x 750): 32.58%; should be 22.23%
3. MacBook Pro 13" Touch Bar (2560 x 1600): 47.96%;  should be 42.67%
4. Apple TV 4K (3840 x 2160): 50%; should be 64%

 
I measured the desktop results fullscreen, multiple times (at least 15 times), since it was difficult to get to the precise edge of the photo. The results were always that between 47.5% and 48.5% of the image was shown on the screen when viewing at 100% zoom, it never got near the 42% it should've been. Interestingly, I also tested Photoshop's 100% zoom fullscreen and it's the same as Lightroom on the desktop. So at least those are consistent, but using screen resolution and basic math they both are not 100% zooms. Perhaps they are factoring 2D percentage, or print resolution. Which causes me to wonder, "what does 100% even mean to the Adobe Lightroom team?"

Perhaps it's print resolution, not screen. Maybe our definition of 100% is wrong, not their math. If so, then viewing 100% based on screen resolution, would be a feature request. While the 200% zoom issue is still a bug.