[Nexus 4 Original Android Development] visceralpsyche:
Color Calibration for the Nexus 4

Thanks for all those of you who provided feedback on my color calibration settings using r72 and Franco's app.

Someone messaged me to ask what the thinking was behind my settings, and I thought it might be worth posting the reasons here too so everyone can understand the why behind them.

Because this thread moves so quickly, here are the settings I'm using again, so you don't have to go searching for them:

R 175

G 175

B 175

Whites 20

Mids 100

Blacks 255

Contrast 0

Brightness 0

Saturation 200

Grays 0

Screen Brightness 50%

These settings provide a VERY close approximation to my calibrated PC monitor when studying my photos in detail (I'm a cinematographer and photographer by profession - see here: http://www.visceralpsyche.com).

A lot of you love the settings, but some of you also say they are too dark, or wonder why you can't put a lower screen brightness and compensate by increasing the RGB values to let more light through.

To understand why I chose my settings, you have to remember that our displays are made up of two parts - the backlight (screen brightness control in Android) and the LCD panel itself (adjusted by Franco's app), which the backlight shines through.

What I found with my testing was that with RGB set to 255, specular highlights (and white edges in general) tended to blow out, causing color fringing artifacts. This is easily seen as pink or yellow edges to what should be pure white images. As I pulled back the RGB values, this fringing began to get smaller, until by my settings of 175 there was no longer any color fringing to my whites. Think of it as a form of highlight recovery. By pulling the clipped channels down equally, I found the point at which the values didn't overflow the hardware limitation of the LCD panel itself.

Once this was done, I went into the gamma interface and began looking for where the whites and blacks ran close to the limit, but not over. I adjusted the screen brightness to where I could distinguish the bottom and top values as individual shades. THis was close enough to 50% that I set it to 50% and tweaked it to be perfect.

Then I played with the Mid and Gray values until middle grey was indeed in the middle, so that the tone curve wasn't biased to one direction.

From there, I adjusted saturation to match my PC monitor's saturation level.

After all that, I arrived at the values I posted above, and now have a screen which faithfully replicates the tonality of my photos without any artifacts or strange tone curves.

If you want to test these values (or your own) I recommend the following images. The calibration chart is one I found online a long time ago, which is useful for seeing the top and bottom end of white and black, to make sure your screen is showing you all the proper values:

The photo is my own, and is useful because I know exactly how I processed it and therefore that it touches both the white end of the spectrum (the highlighted side of her face, with values at precisely full white) and the black end of the spectrum (the fine detail in her hair, which is very black but not crushed in the details):

You can also use her facial tonality to make sure you see a smooth transition through the grays, not steps.

It's also black and white, which means that any color fringing you see is entirely due to artifacts introduced by errors in the color or gamma settings and not the backlight of the screen).

Both images are hosted on my own server, so there are no compression artifacts introduced by the forum.

Again - my aim with these settings is to give you a proper, reference screen that displays accurate colors without any artifacts or errors. Brightness is set to match a proper reference display (120cd/m2) and may be brighter or darker than you prefer.

If you value absolute battery savings over accurate color, then these settings may not be for you. That's perfectly ok of course. But for me, in my line of work, I value accuracy over the little bit of battery savings I might get by lowering my screen brightness, so if that's your goal too, then you'll find these colors are a good basis for having the best possible photo viewing screen on any phone.

Because I can tell you, I have never had a more accurate screen than the Nexus 4 when it comes to looking at my photos, when combined with Franco's fantastic color interface and kernel.

Hope this helps!

Cheers,

Paul Leeming

Writer/Director/Cinematographer

Visceral Psyche Films

http://www.visceralpsyche.com