Hi, sorry if this is a dumb question, but I have been using darktable on my Mac for more than a year and, just recently, when I decided to start working along with other software (Photoshop) I noticed that darktable and Photoshop have different “ideas” on what 100% magnification is. The image darktable displays at 100% is what I would get when looking at it at 200% on Photoshop. I have decided to compare it with Capture One Express, and I noticed the same difference: to get the same magnification darktable gives me at 100%, I need to look at it at 200% on C1 Express. Does anyone know the reason for this difference, and in which software I should probably trust for giving me the “real” magnification?
Thanks!
I suspect this has something to do with the resolution of your Mac screen. You know you probably get the real 100% on that screen if you view the photos at fit-to-screen or maybe 50%. Everything else is actually cheating. What’s the size of your photos and what’s the resolution of the screen?
Conclusion: don’t trust any software.
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The resolution of the screen is 2560x1600 and 227ppi.
My images are 6000x4000
This difference between softwares is not an actual problem, anyway, but it made me curious.
It’s surprising that it’s that way around but I assume there is probably some scaling of the apps to make the gui a readable size. Perhaps it scales the view along with the icons and menus. I would have expected native apps to be more sophisticated than ported gtk apps but perhaps not.
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On Macs you have to consider how the OS is managing the “retina display”. I’m thinking of how icons have to be managed for website, either 1x or 2x depending of the screen. So on macs, 1 physical screen pixel is not always 1 image pixel. I guess the OS is telling the software of this and the app decides the multiplication factor (or not).
I noticed the opposite when using Flyingmeat’s Acorn. A 100% zoomed image looks twice as small as it would in Preview.
I don’t think there is a right or wrong from Darktable or Photoshop or Acorn, I would suggest to open an image in Preview (because it is made by Apple, it has “higher chance” to display the “best” size), and compare in Photoshop and Darktable which one is closer. Acorn is definitely far 
Good idea. I have compared what I get in Preview and it just matches what I get in darktable.
Thats pixels-per-dot (PPD) and indeed a software may use it or not 
dt respects that so the image “seems” to be enlarged twofold. It’s the way to handle high resolution displays showing things large enough without using a magnifying glass.
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Sorry to jump in, but I am pretty sure that Lightroom is correct when zooming 100% and Darktable is actually zooming to 200%. I have just checked using the native screen resolution on a MacBook Pro (2560 x 1600 at 227 PPI), and a picture zoomed in at 100% in Lightroom yields the correct length measured with a ruler. Can it be that Darktable is not reading correctly the native screen resolution?
This has just been fioxed in dt master 