Lightroom CC for mobile: Double tap for accurate 100% zoom on iPad Pro

  • 6
  • Problem
  • Updated 7 months ago
  • (Edited)
Seems that double tapping to zoom in Lightroom Mobile on iPad Pro is inconsistent and never yields actual 100% image pixel to display pixel view. Initial zoom factor appears to depend on actual image file resolution and is about 75% zoom with image files from my D500, but closer to 50% zoom with files from my D850. Repeatedly double tapping eventually yields something closer to 200% zoom for image files from both cameras. I’ve seen a few posts dating back a year or more on this subject and none have been answered. Are there implementational issues with iOS and/or certain mobile devices with adding this functionality? Needless to say an accurate 100% pixel to pixel view is a very important feature to be able to consistently assess image sharpness/detail and noise.
Photo of Roy McLaren

Roy McLaren

  • 44 Posts
  • 7 Reply Likes

Posted 10 months ago

  • 6
Photo of Victoria Bampton - Lightroom Queen

Victoria Bampton - Lightroom Queen, Champion

  • 5169 Posts
  • 2021 Reply Likes
Zoom resolution will depend on how the photos got to the device. If they were uploaded through Lightroom Classic, the full size originals aren't available. Those are only 2560px long edge, with 100% being 100% of that. If they were uploaded through any Lightroom CC app, then they should be a true 100%.
Photo of Roy McLaren

Roy McLaren

  • 44 Posts
  • 7 Reply Likes

Hi Victoria, thanks for the response. Yes, I am aware of this. My images are full size originals uploaded direct from camera to iPad Pro and then added directly to albums in Lightroom Mobile. File information in Lightroom CC mobile confirms full resolution original files, yet I am unable to achieve a true 100% zoom. All my files are stored in cache on the iPad. I have changed settings to locally store original files, but that makes no difference to this issue. I have seen same subject being discussed in other postings with same answers being offered and that's where discussion seems to end with no resolution. Any ideas?
Photo of Victoria Bampton - Lightroom Queen

Victoria Bampton - Lightroom Queen, Champion

  • 5169 Posts
  • 2021 Reply Likes
Hmmm. Can we get some screenshots of the different stages then? That might offer some clues.
Photo of Roy McLaren

Roy McLaren

  • 44 Posts
  • 7 Reply Likes

Yes, I'll try to do that tonight. In meantime here are some additional details:

All my image files are synced with Lightroom Classic on my desktop, but just to underscore I have originally imported files to iPad and then used Lightroom Mobile to add files to Lightroom Mobile albums. The process is entirely managed on the iPad. Fact that I am then syncing images to Lightroom Classic on my desktop is secondary and should not affect anything.

Also to clarify what I regard as true 100% zoom. If we take my D850 full res images as an example. These images are 8256 pixels long. The 13" iPad Pro screen resolution is 2732 pixels on long axis. This means that at 100% zoom apprx 1/3rd of image should be displayed over the full screen on the long axis. This is never the case. Initially when opening an image and double tapping ~2/3rd's of the image is displayed along the long axis implying around 50% zoom factor. When repeatedly double tapping same image it eventually jumps to higher zoom where apprx 1/6th of image is displayed along long axis. This implies ~200% zoom factor. For true 100% zoom apprx 1/3rd of my D850 image files should be displayed along long axis, right?

Another point is I have same problem with files from my D500, but first zoom ratio is different. With D500 on first opening image and double tapping, again apprx. 2/3rd's of image is displayed on long axis. This time though this implies a 75% zoom factor due to the lower sensor resolution of the D500. When repeatedly double tapping I will again see zoom factor suddenly jump and with D500 files this time with apprx. 1/4 of image displayed along long axis. This corresponds to 200% zoom factor which is same as with D850 files.

So basically 1) when first opening an image and double tapping to zoom, the zoom factor will vary depending on image file resolution, in this case 50% zoom for D850 and 75% zoom for D500 full res. images, and 2) when repeatedly double tapping zoom factor will eventually pop in displaying apprx. 200% zoom factor for both D850 and D500 files.

Regarding process for importing files to iPad and then to Lightroom mobile, here are my steps:

1) Connect XQD card from camera via card reader to iPad Pro
2) iOS Auto import window pops up
3) Select images to be imported and import
4) Open Lightroom CC Mobile on iPad Pro
5) Create new album in Lightroom Mobile
6) Select add photos to album
7) Select images from iOS "last import" and add images to Lightroom album
8) Once images are in Lightroom Mobile album I delete images in the iOS "last import" to prevent uneccessary iCloud storage space use
9) That's it, and then Lightroom Mobile proceeds to upload image files to Adobe Creative Cloud. I am allowing unlimited cache size to maintain local copies on iPad Pro. I have never performed clear cache.

When I then review images in Lightroom mobile I initially see message "Smart Preview" in the file information display and after few seconds changes to "original". Full image resolution information is available and displayed correctly. However zoom function is as described above.
(Edited)
Photo of Roy McLaren

Roy McLaren

  • 44 Posts
  • 7 Reply Likes
Hi again Victoria. I’ve given a detailed verbal description above. What specific information would you like me to capture in screenshots to help along a resolution? Thanks.
Photo of Roy McLaren

Roy McLaren

  • 44 Posts
  • 7 Reply Likes
Hi Victoria, here is a selection of screenshots. I wasn’t really sure what information to show you. I just updated to version 4.1 and zooming behavior is unchanged.

1) Processed RAW (NEF) file shot on my D850 and imported to Lightroom mobile as described above. As you can see it is original file at full resolution.

Photo of Roy McLaren

Roy McLaren

  • 44 Posts
  • 7 Reply Likes
I am trying to upload additional images but getting an internal server error. Presumably files exceed 2MB. Not actually sure what additional info I can provide to prove this zooming behavior? I am following a standard approach to get my image files from the camera to Lightroom mobile on the iPad.
Photo of Rikk Flohr

Rikk Flohr, Official Rep

  • 5980 Posts
  • 1317 Reply Likes
Thanks for the detailed feedback, Roy. I've put your thread in front of the Lightroom CC for iOS team for review.  You don't need to upload the additional screenshots that Victoria requested. (unless she really wants to see them...)
Photo of Victoria Bampton - Lightroom Queen

Victoria Bampton - Lightroom Queen, Champion

  • 5169 Posts
  • 2020 Reply Likes
> (unless she really wants to see them...)

I can live without them! ;-) Getting it in front of the team was my main aim, so thank you!
Photo of Roy McLaren

Roy McLaren

  • 44 Posts
  • 7 Reply Likes
Thanks Rikk. Couple of additional observations. I need to check but seems as if initial zoom factor may have changed a bit with the new v4.1? Slightly higher zoom factor >50% but still definitely not 100%. Repeated double tapping still results in 200% zoom. Thing is number of double taps to get to 200% zoom is inconsistent. It can happen quite quickly with some images, but may require multiple double taps in other cases. Once it starts though double tapping will consistently result in 200% zoom. Only way to stop this is to select a new image and go back to previous image again. Then process repeats. I also use Apple Pencil and I think the jump to 200% zoom occurs more readily with that rather than finger tapping. Although behavior also occurs with finger tapping might be less frequent. Either way the initial zoom factor is never a true 100%
Photo of Prasand J.

Prasand J.

  • 32 Posts
  • 10 Reply Likes
Perhaps this is more of a feature request than a problem, but I agree it would be a great feature for “pixel peeping”. Having Lightroom perform consistently / predictably no matter which camera is being used, is a boon. Programmatically it’s actually more complex to adapt to / vary based on camera, than having a basic 100% zoom.
(Edited)
Photo of Roy McLaren

Roy McLaren

  • 44 Posts
  • 7 Reply Likes

I initially entitled my thread with wording "feature request", but an administrator must have removed that wording. Point is true 100% zoom is supposed to be a supported feature with Lightroom Mobile already, so in that sense it was correct to call this a "problem".
Photo of Roy McLaren

Roy McLaren

  • 44 Posts
  • 7 Reply Likes
So, I have compared zoom behavior of original files directly uploaded to my iPad from camera to Lightroom mobile with smart previews originally uploaded to my desktop and synced via Lightroom Classic, and the zooming behavior is identical. In Lightroom Mobile on iPad (and in this case with D500 NEF files) double tapping on a newly opened image shows about 2/3rd’s of image along the long axis. On 13” iPad Pro this is a zoom factor of approximately 75% give or take. This zoom factor remains the same regardless of whether I am reviewing original images or smart previews. Repeated double tapping will, as discussed above, eventually result in a significantly higher zoom factor of about 200%. Once again I see exactly same behavior with both smart previews and original files. No difference.
Photo of Prasand J.

Prasand J.

  • 32 Posts
  • 10 Reply Likes
Odd, it sounds as if you’re getting more than two zoom levels upon double-tapping repeatedly. However, I only get two, “fit” and then something that I thought was greater than 100% before, but in hindsight realize it was the smart preview. Upon downloading the original I saw it’s probably 100% . Repeated double-tapping just causes it to go back and forth between “fit” and what I assume now is 100%.

I am using the new iPad Pro 11”, on the latest Developer Beta of iOS, and the iPhone 7 also on the latest Developer Beta. Behavior is the same for both devices, only two zoom levels. I do not use Lightroom Classic and never have. So it causes me to wonder if although the files originated from iOS import, something about Lightroom Classic is mucking up the zoom levels.
(Edited)
Photo of Roy McLaren

Roy McLaren

  • 44 Posts
  • 7 Reply Likes
I’ve been on the road a few times and uploaded images directly to my iPad from camera and prior to images being synced with Lightroom Classic have exhibited same zoom behavior I have described above. So don’t think the sync to Classic is responsible for the issue. Yes, the normal behavior should be as you describe, but in my case I am indeed getting two different zoom levels.


I’ll clearly summarize how all different types of image tapping options behave for me:


1) Single tap on image toggles between regular view (with menus) and full screen fit - this works fine


Rest below assumes full screen mode as starting point:


2) First time double tapping on newly opened image (two taps in very quick succession) yields a zoom factor < 100% and depends on image file resolution, e.g., in my case with 13” iPad Pro zoom factor is 75% for D500 and 50% for D850 full resolution NEF files respectively. This is the main issue. According to Lightroom Mobile documentation this should provide a true 100% view, but it does not.


3) Repeat double tapping after zooming in returns image to full screen viewing size


4) If I then repeat double tapping to zoom in and out multiple times the zoom factor will eventually pop to 200%. Behavior is same regardless of image file resolution. I will see 200% zoom factor on both D500 and D850 NEF files. The big variable here is there is no consistency in number of repeated double taps for zoom factor to jump to 200%. Sometimes it happens quite quickly, other time I have to repeat double tap many times to get it to happen. However once zoom factor has jumped to 200% then further double tapping will always toggle between full screen view and 200% zoom, never the lower zoom factor that occurs initially. Also seems that jump to 200% zoom happens more readily with Apple Pencil rather than with finger tapping, but can also be induced with finger tapping.
(Edited)
Photo of Prasand J.

Prasand J.

  • 32 Posts
  • 10 Reply Likes
The resolution of my files are 24mp (6000x4000) Leica DNG, and 12mp (4032x3024) Lightroom DNG (taken with my iPhone). On the 11" iPad with a resolution of 2388x1668, 100% zoom on the 24mp image would be 39.8% of the image displayed. It came to mind that I could use Lightroom's 100% calculation behavior itself to trigger the glitch, by forcing it to calculate while changing the orientation of the device. I was able to successfully get the 200% zoom to trigger, and narrowed the steps down to:

  1. With Lightroom CC on iPad completely exited from the open tasks, I opened Lightroom CC while holding the iPad in landscape orientation. If Lightroom hasn't been completely closed yet, open an image ... and make sure to close any open panels. Exit the image to get back to grid view. Then completely close the app from the task switcher while you're in grid view, and open it again.

  2. With LR open, I opened one of the 24mp landscape images using a single click. The photo opened in "fit" mode.

  3. Double-tapping the photo caused it to zoom in so that the 1/2 of the image could be seen at once (which is actually less than true 100% zoom).

  4. Double-tapping the photo again causes the image to zoom out to "fit". Subsequent double-taps just cause it to go back and forth between zoomed-in and fit.

  5. While the image was zoomed-in I rotated the iPad to portrait orientation.

  6. While the iPad was in portrait orientation I opened the info panel with the image zoomed-in.

  7. With the info panel open, double-tapping the photo resulted in it zooming out to "fit".

  8. Double-tapping it again causes the image to zoom to 1/4 of the photo's width.

  9. Double-tapping it again causes it to zoom out to "fit".

  10. I closed the info panel while the image was in "fit" and the iPad is held in portrait orientation.

  11. Double-tapping the photo again causes the zoom behavior to break. In my case the zoom showed 1/8 of the image or double the previous 1/4 it was giving. Thus becoming a 200% zoom (not a true 200%, just 200% relative to the previous 100%).

  12. Once the zoom behavior breaks it stays that way, whether the iPad is held in portrait orientation or landscape. It consistently goes back and forth between 200% and "fit".

Those steps do not always trigger the break, but it does it consistently enough for me to call it reproducible. If those steps do not work, exit the app completely and try it again. Or just add rotation to the double tapping to increase the probability of triggering the break. The opening of the panel introduces another level of complexity in calculating the position while calculating the zoom level, further increasing the chance of a break.

Point is, it's reproducible despite having never used Lightroom Classic.

My previous assumption that it was doing a 100% zoom is because I was eyeballing the lower resolution images on a smaller screen rather than actually measuring it. But having measured it I see that at no point was the 100% zoom truly 100%.

I imagine the zoom calculation is taking ppi into account, causing the 100% zoom to be incorrect due to the variance of ppi in displays (that or doing something like dpi to ppi math). If the math were based purely on resolution, I doubt there would be room for glitching.
(Edited)
Photo of Roy McLaren

Roy McLaren

  • 44 Posts
  • 7 Reply Likes
Great that you took time to investigate this in detail! So, we can clearly state that based on our findings that a true 100% zoom is not available in Lightroom Mobile on iPad, although it is supposed to be a supported feature. That is when defining true 100% zoom as matching one image file pixel to one iPad display pixel and assuming all else is equal.

I always view my photos with iPad in landscape orientation as I am also using Apple keyboard. I don’t need to change iPad orientation to trigger the jump to 200% zoom and for me doesn’t require a great deal of effort to trigger.

Thanks again. I’ am very interested to hear Adobe’s feedback on this matter.
Photo of Prasand J.

Prasand J.

  • 32 Posts
  • 10 Reply Likes
I wanted to define predictable triggering so it could be troubleshot. A precise triggering method might illuminate where to look, as it could be due to an overlap of events. Hopefully it'll help them get to the bottom of the problem. Or maybe they can just redo the zooming math, since it's inaccurate anyway.

There's a limitation with the iOS SDK in relation to screen size (UIKit's UIScreen nativeBounds property). If the "base SDK" being used for the sake of device compatibility, is too low, it will cause the screen of newer devices to be reported as smaller than reality. It's possible that wasn't compensated for. -- Ultimately, it could be any number of reasons, not necessarily inaccurate math.
(Edited)
Photo of Roy McLaren

Roy McLaren

  • 44 Posts
  • 7 Reply Likes

Great points, and I'll guess we'll see. Thanks for helping to reproduce issue. There are other reports of this issue. Below are some examples:

https://forums.adobe.com/thread/2561677

https://forums.adobe.com/thread/2406683

https://forums.adobe.com/thread/2530270

I guess some reports have been dismissed due to the Smart Preview caveat, but in my case I have now proven that the zoom behavior and inconsistency is the same regardless of whether I am viewing a smart preview or original file. Was looking for an additional link that I can't find where the Smart Preview zoom exception was brought up but the OP stated he was also only working with directly uploaded original files. So, yes there are other reports out there.
(Edited)
Photo of Prasand J.

Prasand J.

  • 32 Posts
  • 10 Reply Likes
I see, interesting. Indeed @ proven. I imagine the 200% issue wasn’t addressed simply because it wasn’t reproducible. I had not seen that error before forcing it to trigger, so it’s possible that was the case for them.

In regard to the inaccurate 100% zoom, I just checked the App Store and Lightroom requires iOS 11 or later. Which means that SDK limitation issue isn’t relevant (it was addressed in iOS 11). Now I’m pretty sure its just simply incorrect math. After realizing that, I checked LR CC desktop (not classic) and it’s also not true 100% (didn't know which aspect you were saying also happens on Classic, but now I see). Wish I could see those portions of the zoom calculations code.

@ first link ... there should be a small semi-transparent overlay in the bottom left corner or something that shows the level when zooming (the overlay could fade out / disappear after a few seconds). That way users could see the level while pinching to zoom, instead of just guessing. Never saw the need until this thread, but as I was eyeballing / guesstimating the zoom level a few times, I realized how annoying that was, lol. That would be like Photoshop not showing the zoom level.

Does Lightroom Classic show the zoom level?
(Edited)
Photo of Prasand J.

Prasand J.

  • 32 Posts
  • 10 Reply Likes
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.
(Edited)
Photo of Roy McLaren

Roy McLaren

  • 44 Posts
  • 7 Reply Likes
“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.
Photo of Roy McLaren

Roy McLaren

  • 44 Posts
  • 7 Reply Likes
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.
Photo of Prasand J.

Prasand J.

  • 32 Posts
  • 10 Reply Likes
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.
(Edited)
Photo of Roy McLaren

Roy McLaren

  • 44 Posts
  • 7 Reply Likes
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?
(Edited)
Photo of Prasand J.

Prasand J.

  • 32 Posts
  • 10 Reply Likes
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.