Re: Calibration software for an iMAC

David Kilpatrick wrote:
Me wrote:


The 24" Imac screen isn't "one of the best for color accuracy". It's no better - and probably worse - than other currently available IPS panel screens of that size.
The panel is made by LG China (formerly LG Philips) presumably made to Apple's specs - including price. The panel itself is probably fine.

I'm aware of that. Alamy chose 24 inch LG panels for their QC process partly because of the Mac experience, though they are PC-based. I still have some 20 inch Mac monitors around, but it was seeing the 24 inch LG in use which persuaded me the iMac was a good deal.

I understand that the Imac 24" backlight is an array of 3 x CCFL tubes. That's noteworthy because while (cheap) TN panel displays of that size might have 3 CCFL tubes, IPS panels displays usually have 6.
Here's an article which gives a very plausible explanation for the excessive brightness:
"Apple tries to compensate for this with ridiculously high level of brightness"
http://www.silvermac.com/2008/24-inch-imac-display-brightness-problem-and-what-you-can-do-about-it/

Note the comment: "Even the lowest setting is still way way too bright for most of us". I understand that lowest setting gives around 180cd/m2.

This I simply don't understand at all. I am in Scotland, it's not the world's brightest country. I live and work in an 200-year property, not a glass office palace, and my office is lit by a single 100W equivalent energy saver. My iMac on minimum brightness is perfectly matched - 'paper white' - right now with a bit of daylight from an overcast morning coming in through 1/3rd of my window. The exposure for the whole area of my desk is 1/30th at f/2.8 at ISO 100. That includes the screen, which at that exposure is not burned out and looks just right.

If I open the shutters to have a normal window - and an illumination level more in line with office regulations - I need to revert to medium brightness on the screen.

That's "personal preference" (and nothing wrong with that). Many professional grade monitors come with detachable hoods. I think if you look at the specs for some professional Eizo monitors, using them set at a white level greater than 100cd/m2 even invalidates the backlight warranty.

>
I don't have a luxmeter anywhere to hand, but my screen is homogenous in brightness to within 1/3rd of a stop left to right - the hot zone indicated on the website you point to is 1/3rd stop brighter, with the backlight at full power, than the right hand end of the screen. Actual brightness level from a white area - 1/50 f/6.3 (left) f/5.6 (right) at max brightness, camera with lens set to infinity place against screen.

All CCFL backlit screens have significant non-uniformity. Eizo correct for this with their premium range by in factory measurement and adjustment from hardware LUT, and guarantee non-uniformity < Delta E 3.0. (one I saw had factory calibration data showing Delta E well below the 3.0 maximum)
Most screens tested by TFT Central for non-uniformity show deviations of about +/- 15%.
It will be interesting to see (when they test one) if white LED backlit screens improve on this, or if non-uniformity patterns are just different. White LED backlighting is only a stop-gap trend, as RGB LED is a much much better concept for colour accuracy, power use, and backlight longevity. Already LG must be giving Eizo, Lacie, NEC etc some cold chills by announcing this:
http://www.displayblog.com/2009/03/17/lg-w2420r-24-lcd-monitor-with-rgb-led-backlight/


I'm aware of the failings of the iMac 24 - it can lead users into thinking they have worse problems with noise in digital camera files than they do, through quantisation of close blue tones in sky gradations.

Maybe we get a different specification in UK/Europe? On very bright days, if I want to work with my window unshuttered, the screen looks quite grey and I have to close the shutters to do photo editing. I've been in offices in the US which are a blaze of light, or have levels of natural light much higher than I would expect here.

This is the only thing I don't really 'get' - why people think the iMac 24 (at least the beige/acrylic version like mine) is over-bright. It's probably the most comfortable screen I have ever used.

I've used Imac 24s, and I actually do quite like them, and there's no doubt that they're a quantum leap ahead of the computers (with LCD screens) that most people use. They use IPS panels - so the best panel technology. Brightness /is/ a personal preference. But the concept that Mac hardware is for some historical reason "better" for graphics / photo editing is wrong. Even the best Mac branded hardware (ACD) fall well short of professional grade equipment from other makers.
.

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