Introducing LCD Scrub

…or, the story of how I really saved my screen.

Every piece of software available here at toastycode exists first and foremost because it was something I wanted to use and, finding it not to exist, had to go about creating it. Pyrothèque is a perfect example: I had fond memories of Pyro!™—perhaps the granddaddy of all screen savers—and wanted to bring its iconic B&W fireworks back for a revival.

OK, now that that’s out of the way, let’s talk about LCDs.

At my office I have my Mac workstation hooked up to a 19″ flat-panel display from Dell (the 2001FP). I drive it over DVI at native resolution (1600×1200), which is totally sufficient for my multitasking needs.

April 25, 2007

One sunny Wednesday morning, I arrived at my office to find this:

Fig. 1.   Uh oh.

The standard “Computer Name” screen saver was running1, but something was very, very wrong. Bright green lines streaked down the black areas of the screen, while green echoes smeared rightward off displayed images. The entire screen was dusted with stray green pixels, sparkling and popping like TV snow.

Not good.

Fig. 2.   Detail.

It turned out that my officemate had used my iSight/iChat setup the previous evening. He must have swiveled the monitor around when he was finished; it was torqued so far out of position that the DVI cable came loose (with a few bent pins for good measure). Somehow the cross-talked DVI signal resulted in the green noise, which danced on my screen all night long.

The video, it burns

Here’s where it gets interesting. When I replaced the DVI cable, the screen almost went back to normal: my Mac’s screen was now covered in dark shadows where the searing green had been. It was like having CRT burn-in.

I continued using the monitor for the rest of the day, but the lines were distracting, irritating, and deeply concerning: I didn’t want to have to tell my adviser that I’d busted my shiny LCD panel2. I turned it off overnight, hoping to release whatever bad mojo had found its way in there, but when I powered it back on the next morning, the lines were still there.

I turned the display off when I went home, and over the course of normal use over the next few days, the ghosts faded a little, but were still pretty annoying. I came in a couple of days later with a better camera3 and took some close-up images of the burned-in areas:

Fig. 3.   The most persistent ghosting occurred toward the bottom of my screen; it still hadn’t cleared after a few days.

Over the weekend I did some research. I had always assumed that flat panels couldn’t get burn-in4; it turns out I (along with countless LCD salespeople) was mistaken. LCDs can instead get image persistence (aka image “retention” or “ghosting” or “traces”), and manufacturers disagree as to exactly why it occurs; perhaps stray charge, maybe combined with heat and “ionic impurities”, or some other abstruse electrochemical condition.

What is universally acknowledged is that one image, displayed for a long time, will tend to leave an after-image on an LCD screen or TV. High-contrast static images (like my green lines) are the worst. There also seems to be some consensus that Dell displays are particularly prone to this sort of thing. Lucky me.

Prevention and repair

The common recommendation, from manufacturers and message boards, is: don’t leave a static image on your screen. (So keep using those screen savers, folks.) Which is all fine and well, but what to do with a screen that’s already burned?

Finally, some good news: it turns out that image persistence is usually reversible (something that was never possible with CRTs). I quickly found Apple’s recommendation for eliminating image persistence: Create an all-white image in Photoshop and set up the photo-album screen saver to use just that one image. (Other manufacturers and forum posts also recommend displaying a solid white image.)

I tried the solid white image technique for a day, but for whatever reason, the lines were still there. After reading the NEC white paper talking about fixed high-contrast images causing persistence, though, I wondered: Could I use moving high-contrast images to “scrub away” and smooth out the excess electrical charge (or whatever it is that causes the problem)?

Scrubbing solution

I set about building a screen saver module that would let me try different high-contrast patterns to see how they fared. Furthermore, since patterns with thin bright lines caused the problem, I set about using similar line patterns to ameliorate it.

It worked.

After a day of using the high-contrast patterns, the lines were almost invisible; the next day they were gone.

Fig. 4.   My dock and Trash, after a couple of days of pattern-based LCD scrubbing.

So, to recap: Dan’s LCD is hosed; Dan does a bunch of Internet reading, tries a bunch of stuff, creates a solution that works; Dan doesn’t have to get a new monitor. Q.E.D., the end.

An epilogue—and also a preface

I thought I was done with LCD scrubbing forever; with my display fixed, my screen saver properly configured, and my DVI cable securely screwed to the back of my display (!), I was free of the whole issue.

And then I started hearing, from friends and family who had heard the sob story of how my monitor was ruined and how I fixed it, that I should make this tool available to everyone. “Our office’s IT guy just threw a few LCDs away,” said my brother-in-law. “They had burned-in logos and patterns, and we couldn’t use them like that. I told him about your scrub thing, and he said, where can I get that?

“Don’t you sell software?” he added, somewhat irritably, to my blank stare.

So, here we are: A few months later (well, more than a few; it’s been a busy time for my other career), I present LCD Scrub 1.0.

LCD Scrub: busts flat-panel ghosts

It’s a descendant of the same screen saver I wrote for myself last spring; to use it, set your energy saver settings to never turn off the display, and your display settings to your LCD panel’s native resolution. Then select LCD Scrub as your screen saver, pick a pattern, and let it run overnight. If you don’t see any improvement, try another pattern.

You can download a trial version from the LCD Scrub page; it will run for 20 minutes so you can see how it works and decide if you want to purchase it. The full version (without time limits) costs just $18.

If LCD Scrub doesn’t work on your display, shoot me an email (with photos of the problem, please) and we’ll try to figure out how to improve the software. I can’t guarantee that it will work in every case of image persistence (having only a limited set of screens to test it on) but, as it uses Apple’s recommended techniques along with my additional high-contrast patterns, I expect it to be effective on all but the most severe cases of image persistence.

Download LCD Scrub and give it a shot.

1 Don’t worry, Pyrothèque was running on my PowerBook.

2 Which might mean having to buy a whole new display. From Dell’s support document on “burn-in”: Image Retention (or “burn in”) on LCD flat-panel displays is consider [sic] improper use of the display and is not cover by Dell’s limited warranty. Yikes.

3 Well, better than my cameraphone, at any rate.

4 And, consequently, I felt a little foolish using screensavers all the time.


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