Exported and previewed pictures appear to have different PPI

[martin_krizka]

Hello all,

I am having some pixelation issues of exported jpegs (from DNGs) so I wanted to narrow down the problem to eliminate problems with resolution change during export.

MacBook Pro 2017 (13inch) with Lightroom 6.14, Camera Raw 10.1. (have experience with PS on Win computer)

Thus I:

1 - imported a DNG fine into Lightroom
2 - exported the file into jpeg with settings in the attached screenshot
3 - opened the jpeg file in Apple Preview (Actual size option)
4 - compared it with the source DNG file in the Develop module of Lightroom

5 - and I can not understand why they are different

I am using the Scaled / More space built in screen setting but it looks same on the default setting.

Any thoughts please?
Martin

[dj_paige]

They can't possibly have different PPI because digital images are not measured in inches.

Could you please show us both images at 1:1 zoom?

Could you please clearly state what the differences are that you see? I am not seeing any pixelization.

[JP Hess]

It seems to me that the Lightroom 1:1 view is taking up less screen real estate than the other view. I think it's just a difference in scaling between the two applications. It isn't a difference in PPI because digital images don't really have a PPI setting. They have pixel dimensions, and those pixel dimensions are not affected by any PPI setting.

[Per Berntsen]

You have to view both images at 1:1 to compare them.

You are definitely viewing at less than 1:1 in Lightroom.

The image in Preview is pixelated, so I wonder if you have a Retina display, and that Preview is scaling the image to 200%.

Just a guess, I don't use Mac.

[martin_krizka]

Thank you all.

PPI wasn't the right expression, my bad.

dj_paige​ Per Berntsen​
Both pictures are 1:1. The zoom slider is a bit confusing UI problem of Lightroom in my opinion - the ratio is changing as you move it and stops at 11:1. It would be more appropriate to have the 1:1 located just above the teardrop slider pointer.

JimHess​ Your "scaling" comment is rather close.

I tried to open the exported jpeg picture in Safari, Chrome and it looks same as the one opened in Preview - all are 1:1.

I just did the same comparison on my external office screen and the problem completely disappeared - images look identical in Lightroom and Preview, no pixelation problems event after export with resize.

In such case, the problem seems to go down to the MacBook screen. But still, no idea why 😕

[Per Berntsen]

Yes, you're right, you are viewing at 1:1 in Lightroom.

I did a search for your computer, and it does have a Retina display. As far as I can tell, you have a 13" display with a screen resolution of 2560 x 1600. So the display has a ppi of 227 (227 pixels per display inch), which means that the pixels have to be very small. Or in other words, the pixel density is high.

Smaller pixels mean smaller images, and Preview (and web browsers) will scale images to 200% when they detect a Retina display, to make them larger on screen. Lightroom cannot do this scaling, because it has to display images correctly - i.e. using one screen pixel to display one image pixel.

I just did the same comparison on my external office screen and the problem completely disappeared - images look identical in Lightroom and Preview, no pixelation problems event after export with resize.

This is because the external screen is non-Retina, it has a much lower pixel density, so Preview doesn't scale the image to 200%.

[martin_krizka]

Per Berntsen​ This makes perfect sense.

Is there any reason why the images are scaled to 200%? (and not a different percentage)

[JohanElzenga]

martin_krizka  wrote

https://forums.adobe.com/people/Per+Berntsen  This makes perfect sense.

Is there any reason why the images are scaled to 200%? (and not a different percentage)

With a retina screen or a 4K or 5K screen, your hardware screen resolution is normally higher than the display resolution set in your system preferences. That makes sense, because otherwise your menus and other interface items would become too small. If the interface items were drawn in this lower display settings resolution however, they would effectively be upscaled when shown on the screen. That would look bad, so the following trick is used. The applications draw their interface items at twice the display settings, and then these get downscaled to the hardware resolution. That looks much better and allows different display settings on the same hardware. That’s why Lightroom also displays at 200% when you set the view to 1:1 on a retina display. Adobe could have used the real hardware resolution in that case (and maybe they should have), but then people would complain that zooming in to 1:1 results in a smaller image than on their old low resolution screen.

[Per Berntsen]

I think 200% was chosen because a typical Retina display has a pixel density roughly twice as high as a typical non-Retina display.

(2560 is twice the size of 1280 and 3840 is twice the size of 1920).

JohanEl54 wrote

That’s why Lightroom also displays at 200% when you set the view to 1:1 on a retina display

I don't have a Retina display myself, but I'm pretty sure it doesn't.

Lightroom is a professional image editor, and has to display images correctly - one screen pixel for one image pixel at 1:1.

It's also evident from Martin's screenshot from Lightroom that the image has not been scaled - it's crisp and clear.

[JohanElzenga]

Yes, I’m sorry about that. It seems the opposite. Preview shows the image at 200%, Lightroom shows it at the real native resolution. That is why the image in Preview is bigger.

I believe the 200% factor was chosen because interface items can be upscaled (using nearest neighbor) much nicer to 200% than to an intermediate resolution. Not every application is ‘retina ready’ and not every UI item is vector based.

[JohanElzenga]

When you change the display resolution, Lightroom changes the size of the standard previews. You can check that in the catalog settings. So what I said about Lightroom is correct as far as thumbnails and loupe view are concerned, but not when you zoom in to 1:1.

[D Fosse]

martin_krizka  wrote

Is there any reason why the images are scaled to 200%? (and not a different percentage)

Because 200% is a clean upscale - one image pixel represented by exactly four screen pixels. No sub-pixel resampling, no reduction in image quality. Just a clean pixel doubling.