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Photoshop Scaling Bug

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Tested with Photoshop CC 2014 version 20141014 r.257 using OS X Yosemite 10.10.1.

For this discussion, “actual pixels” means 100% scale meaning one image pixel is drawn to one screen pixel. 50% means two image pixels are drawn in one screen pixel, 200% means one image pixel is drawn on 2 screen pixels, etc.

This is all independent of display scaling; display scaling is designed to affect only text and user interface elements.

These issues are fixed in Photoshop CC 2015.

What follows applies to any brand HiDPI or 4K display (not specific to NEC or other brand).

Photoshop CC does not scale images properly on HiDPI screens. Bug reproduced on these combinations:

But the error also occurs on retina display of the MacBook Pro Retina, showing that it is a general problem not confined to 4K UltraHD displays.

The amount of error varies, but sometimes it is as much as 2:1, e.g., 100% pixels is really 50% pixels, so one has to zoom to 200% to see 100%! The error occurs regardless of the display scaling settings, and can come and go—sometimes right and sometimes wrong. Your author suspects a new bug in OS X Yosemite 10.10, not having observed this issue prior. But it might be Photoshop itself (only).

Up to 1527MB/s sustained performance

Example 1

As shown below, Photoshop is supposed to be displaying at 100% pixels (see very lower left where Photoshop itself shows this scaling) an image of dimensions 5754 X 3200. Yet as the ruler shows, over 5000 pixels are drawn on a screen that is only 3840 wide! Obviously this is not actual pixels! It’s about 75% of actual pixels (~5404 pixels drawn in a 3840 width).

Click for full-res screen image (3840 X 2160).

Photoshop CC 2014: incorrect image scaling

Example 2

The example below makes it painfully clear: the image being displayed is itself 3840 pixels wide (and indeed the ruler matches that), so it should fill the 3840-wide screen at 100% pixels (actual pixels).

Yet Photoshop has drawn it half-size, 1920 pixels wide, which is 50% scale.

Click for full-res screen image (3840 X 2160).

Photoshop CC 2014: incorrect image scaling
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