I bought a new 24" iMac yesterday and.....

[czachorski]

"As for the maximum deviation, the range is more lenient: if it doesn’t
exceed 15% - good, 20% - acceptable, over 20% - poor."

http://www.xbitlabs.com/articles/other/display/lcd-testmethods_4.html#sect0

LK

I think you are implementing their spec slightly incorrectly. From the web site you linked:

After that the deviation in % for each spot is calculated for both data arrays: the white color deviates below the maximum value, while the black – above the minimal.

They are calling out a deviation as a percentage below the maximum, not the ratio of the brightest to dimmest. Using their method, my measurement with the camera would be 20% below the maximum, whereas the ratio of the maximum to minimum is 1.25. A slight difference, but one that puts it in the "acceptable" range using their criteria, rather than poor.

Leon, I feel bad for you on your deal, and do not dispute that you got a bum deal and poor, unacceptable treatment by Apple. But you had a very bad screen with 250% variation, and yet you play it off as if all iMacs, even ones with 20% variation, are defective. I would just once like to see you acknowledge that there are "acceptable" alum iMacs out there, just like I have acknowledged that you got a bad deal, and jumped through every single measurement hoop you have thrown at me, and openly posted the results here, with a very open and honest disposition.

I have learned a lot from these discussions too, about LCDs, cameras, colors, and measuring brightness. I has been a fun discussions when it stays logical and scientific. I thank you for that.

 

[0sync0]

I don't do any luminance adjusting. I do work with a lot of photos and video and can't tell any difference in luminance across them, nor have the 25-30 people who have looked at photos or videos with me on this iMac.

With the Apple Cinema Display testing at 25% as well, I'm guessing that this range is pretty normal amongst LCDs. Perhaps you should broaden you statement to include LCD screens, not just iMacs.

I was thinking about this some more and realized that 25% is only 1/4 of a stop. That isn't as bad as I first thought.

 

[czachorski]

I was thinking about this some more and realized that 25% is only 1/4 of a stop. That isn't as bad as I first thought.

That makes more sense to me too. The screen is very nice, although obviously not perfect when placed under a light meter. I can't imagine someone sitting down in front of this screen as saying "eeeewww - that's unacceptable". Everyone usually sees it and says "wow, what a beautiful computer".

Using the method from the site Leon linked to, this Alum iMac at its dimmest is actually only 20% below maximum brightness. Leon's white iMac is 15% below max. My Apple Cinema Display is also 20%. That 3 LCDs from Apple all in the "acceptable" range from Leon's web site, which doesn't seem surprising to me. I am sure there are "great" LCDs out there, but they are probably higher-end then the panels Apple is using.

 

[vansouza]

....and how do you know that? Have you seen them all?


Mine's not bad. If your is, return it. Don't put up with a visible gradient during normal use. You shouldn't have to tolerate a defect, and there are many many good ones out there. There are threads here that have gotten to 5-10 pages or longer of people with good ones, and the "bad ones" threads seem to have gotten more and more rare.

Thank you... mine is fine, perfect.

 

[czachorski]

Thank you... mine is fine, perfect.

 

[Leon Kowalski]

They are calling out a deviation as a percentage below the maximum,
not the ratio of the brightest to dimmest. Using their method, my
measurement with the camera would be 20% below the maximum,
whereas the ratio of the maximum to minimum is 1.25. A slight
difference, but one that puts it in the "acceptable" range using their
criteria, rather than poor.

Quite right. Xbit's method for stating deviation is the inverse of the industry
standard MAX/MIN luminance ratio. For deviations of a few tens of percents
or less it doesn't change the numerical result much -- but in your case, it was
enough to bump the "Xbit rating" to acceptable. BTW, I didn't intend to hold
Xbit's grading system up as the "Gold Standard" of monitor evaluation; it's
just a ball-park indication of what an LCD buyer might reasonably expect.

I would just once like to see you acknowledge that there are "acceptable"
alum iMacs out there

OK, although I've never seen one first-hand, I'll trust your measurements and
accept that (not that my opinion counts for anything -- your measurements
speak for themselves). But yes, you've convinced me; there are some 24" ALU
"keepers" out there -- hopefully more than a few.

... just like I have acknowledged that you got a bad deal, and jumped through
every single measurement hoop you have thrown at me, and openly posted
the results here, with a very open and honest disposition.

I sincerely appreciate your open and honest posting of measurements, and
believe they're a valuable resource for prospective iMac buyers. Thanks for
your patience and persistence.

best regards,

LK

 

[SaSaSushi]

I have learned a lot from these discussions too, about LCDs, cameras, colors, and measuring brightness. I has been a fun discussions when it stays logical and scientific. I thank you for that.

I sincerely appreciate your open and honest posting of measurements, and
believe they're a valuable resource for prospective iMac buyers. Thanks for
your patience and persistence.

best regards,

LK

Wow, not only did I find this exchange heartwarming but such a convergence of once bitter combatants almost makes me believe there might be a chance for peace between Israel and Palestine someday.

I did some luminance test photos of my own new panel last night at last and it turns out it is better than my old one was.

Great is the power of suggestion. I almost didn't trust my photos.

 

[czachorski]

Cool, thanks Leon. It sounds like we can agree on some very general statements regarding the occurrence of Alum iMacs with defective screens and those with acceptable screens.