iMac screen flashes black in Photoshop CC

Hi,

I’m posting this both in Adobe CC and Apple forums as I’m not sure where the problem lies, but I’d really appreciate help solving this issue:

I’m using Adobe CC apps on a brand new iMac (still in time to get full refund). When using Photoshop CC (2015.5) the whole screen (not just the Photoshop window) goes black for about half a second whenever any tool icon above a certain pixel size goes from tool icon to pointer icon or vice-versa.

This happens for example when the icon comes out of the image area onto the menus or the edge or the window, or when it comes in and out of the right-click change brush size menu. Any situation when it turns from tool back to pointer or pointer to tool. It does not always happens, but it happens most of the time, perhaps the type of movement of the pointer has something to do with it, although it happens both with fast and slow transitions.

The problem only happens when the brush is above certain size – never when it is below that critical size. The critical size may vary depending on whether Photoshop has been opened for a while or just launched (I’m not too sure about this). There is also an interaction with the hardness of the tool.

So for example:

On the Blur tool at 0% hardness the screen flashes black when the size goes above 80 pixels – never below that. At 100% Hardness, it flashes from 64 pixels onwards. Same for the Brush tool, Eraser, etc. I think it happens with any sizeable tool (haven’t tried them all).

I’m using a Wacom Intuos PS and the Apple Magic Mouse. The problem occurs with both, whether they are both connected together or separately.

The problem occurs even when Photoshop is the only app in use.

Please help, as it is pretty much unusable now.

Computer Specs:

iMac, Retina 4k, 21.5 – inch display

Processor: 3.1 GHz Intel Core i5

Memory: 8 GB 1867 MHz DDR3

Graphics: Intel Iris Pro Graphics 6200 1536 MB

Photoshop’s memory usage is set at defaults:

4500MB (70% of available memory)

4 Cache levels

Cache tile size 1024K