I think there are two issues at stake here. There may be some confusion/crossover between what I see as two completely different topics.
Some people may be having issues with how Affinity Photo DISPLAYS images on a high res screen. After switching from an old 2014 Macbook Pro to an iMac (with 5K Retina display) it seems that older images I created with photoshop (viewed at 100% zoom) now appear half size when opened in AF (viewed at 100% zoom).
Initially I found this incredibly frustrating but now I simply increase the zoom to 200% view on AF and all is well. We’re back to where we were back in 2014 Photoshop land!
The only workflow problem here is that it is hard to see what things will look like on a normal (or lower res) screen. You’ve upgraded your gear, and now you can’t go back to the old ways! Your option here is to attach an external monitor with lower res, or - if you are checking images created and uploaded to websites - use a non-attached device to see how things render. The silver lining is that things WILL look ok like they always did - no problem. In fact, they will look BETTER than a hi-res display, as they will suffer from none of the pixelation that occurs when smaller images are projected on a retina-type display.
I feel that this issue is become less of a problem as now most web designers incorporate scripts that will prioritise larger images for retina displays and smaller images for normal displays as the web site loads. Possibly the same thing happens with web-browers? Only poor web designers (like myself!) will be shocked by how once-perfect looking images now look blurry on a Retina display. #mustredsignmywebsiteasap
I know that in recent times PS has incorporated a 200% zoom BUTTON on the main window in order to toggle on/off. This just shows how the recent onset of higher res displays have affected app design.
So, for those of you who have switched to a higher res display then - for now, in AF just zoom in 200% and things will be just as sharp as they were on your older display. By zooming in double, you simply mimic a normal res screen.
This very same issue has been chewed to death on the Adobe Forum. Check it out.
One last important detail for those on Mac OS: Don’t use Preview or Quick Look (space-bar) as a way to judge pixel-accurate size of images. Both Preview and Quick Look scale UP images in order to, again, mimic the look of a older res screen. So, for instance, a 100x100px image will be scaled up to mimic a 200x200px image. The is actually quite helpful as it will tell you EXACTLY how an image will look on a website for instance, if you upload that file. That is unless the website coding prioritises using the image at ‘true’ size. This is the bane of using a Retina display my friends. You have to deal with it. Just don’t use Preview or Quick Look to judge 'true' quality.
This is a bigger issue and one that I think needs addressing on the very next update. There does seem to be a bug when exporting images. AF appears to resample an image whether the image is resized OR NOT on output. I must stress the words: OR NOT. You would always expect some resampling algorithm to be used when resizing on exporting. However, if you choose to export WITHOUT resizing the image, then what resampling needs to occur? In my opinion, there should be a Resample checkbox on the Export dialog so that you can switch off the Resample option should you not change the image dimensions. Or, better still - the Resample algorithm dropdown menu should only be activated when the dimensions are altered. So, I guess that your wondering whether resampling affects image quality when the dimensions on the AF document remain untouched? I bet you’d love to know, right? Well, hell YES, it does affect the quality. And, to this end, I have attached 5 files for you to check out. This is a for a yoga website I am designing. Feel free to download these and load them into AF and flick between them. I have included the working .afphoto document also, so you can check the export quality of the other four .png files for pixel accuracy. You will see that there IS a difference. Files included:
YogaAffinityDoc.afphoto - Original working document (might need to be downloaded to view)
YogaPNGBilnear.png - Exported image using Bilinear Resampling
YogaPNGBicubic.png - Exported image using Bicubic Resampling
YogaPNGLancSep.png - Exported image using Laczos 3 Separable Resampling
YogaPNGLancNonSep.png - Exported image using Laczos 3 Non-Separable Resampling