Sunday, 21 December 2014

Better display quality, printing and the quest for 10 bit colour support

Since I got a nice display (dell U2713H) and got it properly set up I have a good reliable photography workflow on Windows, and with a little work I have the monitor working nicely on Ubuntu as well (This particular monitor requires a pixelclock fix to enable Ubuntu to drive native resolution through the nVidia drivers - see below the break).

My hardware setup is:
  • Asus P8Z77-V LE motherboard
  • Intel i7-3770
  • nVidia GTX 660 Ti graphics card -> display port / hdmi
  • -or- 
  • sometimes Intel 4000 graphics -> display port
  • Dell U2713H monitor
I use D S Colour labs for all my colour printing and can get pretty well perfect match between print preview in Lightroom and the resulting print viewed in a viewing box. However even with Lightroom / Photoshop I still sometimes see banding while working on photos  and it is easy to show that this is often due to the 8 bits / colour / pixel that is normal for today's computers.

(To see this just make a new image in an image editor and fill it with a gradient with a fairly restricted range of grays, such as from 55 - 65. I was surprised when I first tried this just how obvious the effect is.)

So I started looking around to see if I could get at the 10 bits / channel that my monitor is capable of.

At first it appears that the only way to do this is to by a professional workstation graphics card, but these are dramatically more expensive than their consumer equivalents. Then I found that the nVidia Linux drivers are fully 10 bit capable (usually referred to as 30 bit color) on all relatively recent cards!

After a couple of false starts I set up an xorg.conf file: (this includes the fix to enable 2560 x 1440 -> Option "ModeValidation" "NoMaxPClkCheck")
Section "Screen"
        Identifier "Screen0"
        Device     "Card0"
        Monitor    "Monitor0
        Option "ModeValidation" "NoMaxPClkCheck"
        DefaultDepth 30
        SubSection "Display"
                Viewport   0 0
                Depth     30
And now nvidia-settings reports:
X screen 0
Depth: 30

here is the line from Xorg.0.log:
[     4.600] (**) NVIDIA(0): Depth 30, (--) framebuffer bpp 32
However there are now some wierd artifacts on the screen, so it looks like somone is still outputting 8 bit RGBA.

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