I bought 27” Dell U2713HM monitor to compliment my 13” Retina Macbook Pro. I connected it via Displayport to Mini Displayport adapter and got shocked that resolution was Full HD only.
After some investigation I found that there a so many issues with external displays that I couldn’t believe my eyes. Strangely Apple didn’t resolve most of them. My issue was one of many that is open ever since 10.8 was released.
Please note that HDMI cable will not work. Also if you have a DVI to Displayport adapter, please note that you would need dual DVI adapter, standard adapter only supports Full HD.
How to switch to RGB mode in OS X to fix external monitor resolution and quality
Apparently Display Port uses YCbCr colors instead of RGB by default. YCbCr limits color range and is responsible for display corruption. I stumbled on 3 most common problems with OS X, External monitor and Display port cable.
1. Resolution is FULL HD instead of 2560x 1440
2. Colors are anything but proper colors. Color corruption is very common with lot’s of green.
3. Text is not sharp, instead it’s blurry, barely readable.
You will also notice that Display type is Television under – My mac, System report, Graphic / Displays, look at the last line.
I found a solution in the following forum. Andreas created a Ruby script that changes EDID information so that OS X knows that monitor supports RGB. To fix the problem, visit the forum and scroll down in the comments section. Download patch-edid.rb Ruby script. Open terminal and go to download location. Type ruby patch-edid.rb. New folder will be created with name DisplayVendorID-xxx. Move that folder to /System/Library/Displays/Overrides. After reboot, monitor should show proper resolution / colors / fonts. This could work various with external monitors (22” and 23”) with Full HD resolution that are connected via DVI to DVI to Display port adapter.
If you have issues with playing movies on your Dell U2713H make sure you disable Smart Video Enhance in Monitor menu – Display settings, Smart Video Enhance – Off. Also if you have issues with fonts after resolution is fixed on any other monitor check that Sharpness is set to 50. If problem is still not fixed check that monitor is set to RGB in the menu, you may have to manually set color mode to RGB.
rmbp external monitor not recognised problem was luckily fixed with this solution. It did work for me.
I was curios and tested one of 22” monitors I had I connected on another computer, I was able to fix blurry font problem on 22” monitor with this solution (DVI to Display port adapter). Good luck