Musings on Photography

Persistence of Vision

Posted in equipment, hardware, macintosh by Paul Butzi on May 24, 2008

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Some time ago I wrote about profiling of LCD monitors, and about whether such monitors drift over time the way CRT monitors do. I have more news on this front.

Recently, as part of my effort to keep all the monitors in our house accurately profiled, I generated a new profile for my Macbook Pro. When I did that, I noticed that the response in the blue channel had changed – over time, it took less signal to get a given amount of blue. And my recollection was that this wasn’t the case. It appeared that over time, my laptop screen was slowly getting more and more blue. “That’s weird,” I thought, “I wonder whats up with that?”

And then, in an entirely unrelated event, I installed new map software on a Garmin Nuvi we’ve just bought. The fact that we have a Nuvi is unimportant – what matters is that to load the new software into the Nuvi, I had to run a program that put a colorful window on the screen and then didn’t do much but move the scroll bar for about an hour. Afterwards, to my annoyance, you could see a fairly prominent ‘ghost’ of that window on the screen, no matter what was displayed in that spot. The display of our iMac had, as it were, persistence of vision.

A little research netted me some info on image persistence on LCD monitors. Although everyone will tell you that LCD displays don’t ‘burn in’ the way CRTs do, that’s not quite true. But a panel which is showing image persistence can be restored (in many cases) by displaying either a screen of just white, or a screen of moving patterns to ‘scrub’ the pattern off the screen. The problem is (simplifying greatly) that the transistors in the panel tend to take a ‘set’ when displaying a color for long time, and afterwards tend toward that color. Scrubbing the panel with patterns erases this ‘set’.

The most lucid writing I’ve found on this is here, where Daniel Sandler describes his experience with image persistence on his monitor, and how he solved the problem, and the screen saver he’s written that scrubs the display to eliminate it.

Ok, so I’ve got Dan’s screensaver running on the iMac, and it’s slowly erasing the problem. But that bit I’d read somewhere else about pixels taking a ‘color set’ kept nagging at me, until I put 1 and 1 together to make two, and started to wonder about whether the observed increase in the ‘blueness’ on my laptop might have anything to do with LCD image persistence. Because guess what – on my laptop, I use the default Mac desktop image, because I’m lazy and it’s a decent desktop image. But it’s BLUE.

So now I’m wondering if running the scrubber on my laptop will eliminate the blue drift that I’ve observed. Once I’ve eliminated the problem on the iMac, I think I’ll take a crack at the screen on the laptop, and see. And I’ll check the other LCD displays around here, as well, and look at the profiles.

More, as the TV news says, as the story develops.

5 Responses

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  1. Ed Richards said, on May 24, 2008 at 4:41 pm

    Why not set up the screen saver to blank the screen?

  2. Paul Butzi said, on May 24, 2008 at 4:47 pm

    Setting the screen saver to display a bright white image and then turning down the screen brightness (to save on backlight life) is the Apple recommended solution. We did that last night, and things did improve.

    Just blanking the screen/turning the screen off can apparently help but scrubbing apepars to solve the problem faster.

    In any case, on a machine where you work for long periods of time, some of the display will show whatever desktop image you use, and over time those areas will presumably show some image persistence unless you take steps to erase it.

  3. Dave Kosiur said, on May 24, 2008 at 9:45 pm

    I must have missed something, but where exactly did Daniel Sandler describe his experience?

    Thanks

  4. Paul Butzi said, on May 24, 2008 at 9:51 pm

    Whoops, I forgot the link. I added it. Just in case, the stuff is at

    http://toastycode.com/blog/2008/02/05/lcd-scrub/

  5. […] 20, 2008 Some time back, I wrote about color drift of LCD displays, and about LCD scrubbing to get rid of LCD image […]


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