iMac 24" owners. LISTEN UP!

[Leon Kowalski]

My iMac -- 24" / 2.4 GHz -- display at minimum brightness. Sorry 'bout the lack of sharpness; hand-held at low shutter speed (to avoid screen-refresh-rate artifacts) and moderate telephoto (to avoid pincushion). Woulda been much worse without image stabilization (Canon A710 IS).

1) Solid Aqua Blue, max:min luminance ratio = 2.5:1 (+/- 0.2)

2) Solid Gray Medium, max:min luminance ratio = 2.5:1 (+/- 0.2)

Want to really fry your left eyeball? Grab the large version of either photo,
then zoom-in 'til it just fills your 24" iMac's screen. ...gradient SQUARED!


..."The quality goes in before the name falls off."

LK

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[imacan]

Thanks for the pics Leon, the gradient is obvious on your pics, I am pretty sure there is a slight gradient on mine but certainly not as strong as yours. I will try to post pics with the exact same backgrounds as yours later. Can other members post theirs too for comparison?

 

[Leon Kowalski]

I am pretty sure there is a slight gradient on mine but certainly not as strong as yours.

Then consider yourself "lucky," bro. Three of the four showroom models at the local Apple Store were nearly identical to mine (actually, slightly worse) -- the fourth was nearly twice as bad at 3.7:1 !!!

...everyone, more photos, please!

LK

 

[imacan]

With the same backgrounds as yours (Aqua blue, Medium gray):

 

[whowhat78]

well the third one still has the a slight (very very slight) yellowing tint in the lower right hand corner.

other than that everything is perfect. i am going to keep my eye on it over the weekend but it is really a non issue.

finally one that looks good. 98% satisfied with it for the time being.

again, i will continue to post over the weekend with my findings after spending more time with it.

 

[Leon Kowalski]

With the same backgrounds as yours (Aqua blue, Medium gray):

Thanks, imacan. That's the first one I've seen with the hotspot near the center -- and essentially symmetrical. But, according to my calibrated eyeball, the light:dark ratio doesn't appear to be any better than mine. Can you get a measurement of the max:min brightness ratio?

If your camera permits: select aperture-priority mode @ f8, set 'film speed' to about ISO 100, and meter-mode to 'spot' (if available, it's not critical). Then, with the lens nearly touching the screen, see what shutter speeds the camera selects in the brightest and darkest areas of the display. The ratio of shutter speeds is a direct measure of the relative brightness. For example, if the camera picks 1/20 sec for the hotspot, and 1/8 sec for the darkest area, the "luminance ratio" is just 20/8 = 2.5:1.

LK

 

[suneohair]

For comparison my LG display sticks right at 1/15 all the way around. The slowest I saw was 1/13. So my ratio is about 1.15:1

 

[Leon Kowalski]

For comparison my LG display sticks right at 1/15 all the way around. The slowest I saw was 1/13. So my ratio is about 1.15:1

Yep, that seems very typical of today's garden-variety LCD monitors -- and product-reviewers tend to be ...uh, "unimpressed" by brightness uniformity scores as "disappointing" as 1.2:1.

BTW, the $300 I paid to switch from 20" to 24" was PURELY a display upgrade -- because the 20"/2.4 GHz and 24"/2.4 GHz iMacs are absolutely identical in all other respects. So, if one accepts the (dubious) proposition that the 20" display is worth something, then the 24" display should be worth $300 more. Kinda pokes (yet another) hole in the iFanboy argument that the 24" display delivers "reasonable" performance for its price.

LK

 

[psonice]

Just goes to show what a powerful effect "fervent wishing" can have on subjective judgement. There's no substitute for a heartless light meter.

...

...denial IS NOT a river in Egypt,

LK

I meant it was funny as in laughing material - I previously checked the screen brightness for variation across the screen and there was almost none. And there is no detectable colour variation with the naked eye (at least with mine). The photo looks NOTHING LIKE the actual screen!

Perhaps the screen really does have a fault that the camera is picking up, but if it is, it's not actually visible normally and the camera must be emphasizing it massively.

 

[Leon Kowalski]

I meant it was funny as in laughing material ...

No argument there! ...ROTFLMAO.

...it's not actually visible ... the camera must be emphasizing it massively.

Uh, when I take meter readings from the screen, and meter readings from a photograph of the screen (being careful to drag each area-under-test on the photo to the same position on my display), the observed luminance ratios agree almost perfectly, thank you.

...make of that what you will,

LK


"In the land of the blind, the one-eyed man is king."
-- Desiderius Erasmus

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[jajo]

Sure, here's one. Well, that was funny - I used a mid-grey background, it looked fine, opened the pic in aperture, and it looks terrible. It seems to drift towards blue on the left, darken on the right, and it does look almost yellowish in the middle.

I've checked the colour though, and it's actually slightly blue in the centre, not yellow. I think the fact that it looks more blue on the left tricks the eye into thinking it's yellow. Also look at the thin strip of metal at the top of the screen, you can see it's reflecting the background - and it's darker on the right, just like the screen. I think the darker right hand side is just the camera picking up more reflected light on the left. The red dot is just a reflection of my mouse.

Any idea what could cause the blueness on the left though? I'm assuming it's a camera effect of some sort as it looks grey on the actual screen.

That is exactly how my screen looked and I did see this effect even while just browsing. Just compare solid colors on MacRumours background from left to right...

/ Jacob

 

[Leon Kowalski]

... and I did see this effect even while just browsing.

The gradient doesn't bother me very much on full-screen photos/video, but it becomes intolerable when I'm "just browsing" or reading news/blogs. It's at its worst (for me) when viewing dark text on a light background.

...like right now,

LK

 

[imacan]

Well Leon you have quite an eye for saying that my hot spot was in the middle. I did what you said with my camera and here are the shutter speed values (first row being up left - up mid - up right, second row mid left - mid mid - mid right and so on):

At max brightness

With Aqua blue:

1/50 - 1/60 - 1/50
1/60 - 1/80 - 1/60
1/60 - 1/80 - 1/60

Medium gray:

1/50 - 1/60 - 1/60
1/60 - 1/80 - 1/60
1/60 - 1/80 - 1/60


At lowest brightness

Aqua blue

1/40 - 1/40 - 1/30
1/40 - 1/50 - 1/30
1/40 - 1/40 - 1/30

Luminance ratio max/min of around 1.66 (lowest brightness) to 1.6 (maximum brightness).

Are shutter speed differences really proportional to luminance?

 

[Leon Kowalski]

With Aqua blue:

1/50 - 1/60 - 1/50
1/60 - 1/80 - 1/60
1/60 - 1/80 - 1/60

Medium gray:

1/50 - 1/60 - 1/60
1/60 - 1/80 - 1/60
1/60 - 1/80 - 1/60

Does it mean a luminance ratio of around 1.33 to 1.6 ?

I'd call that a solid 80/50 = 1.6:1 for either screen at high brightness. Just use the max and min values, regardless of whether they fall on the same horizontal line.

For the (newly posted) low-brightness data, it looks to me like: 50/30 = 1.7:1

Subjectively, I would have guesstimated a bigger spread than that -- but I'd be the last guy on earth to argue with a light meter. If you measured lots of points, with the lens up-close to the screen (so that each reading covers only a small area), that's good enough for me.

LK

 

[imacan]

Corrected it before your post.

 

[Leon Kowalski]

Are shutter speed differences really proportional to luminance?

In excruciating detail: http://johnlind.tripod.com/science/scienceexposure.html

Executive summary: Yes.

LK

 

[imacan]

Yes, camera exposure equation says it all,

where
A is the relative aperture (f-number)
T is the exposure time ("shutter speed")
B is the average scene luminance ("brightness")
Sx is the ASA arithmetic film speed
K is the reflected-light meter calibration constant

 

[whowhat78]

my 3rd replacement is a keeper. there seems to be a small (very, very small) brightness drop off on the right hand side which is only visible with a white background. photos look perfect.

after over a month and three different machines, i want to start using this machine. no yellowing which was unacceptable as far as my eyes are concerned.

still have 10 days to change my mind!

 

[tttexxan]

I find this thread ironic.....I have been through 3 imacs to date over the last week all having issues....For clarification this is the first time I have read anything on the yellowing tint of the Imac 24 since buying...However with the first one I noticed this right away...I place a B/W photo on the screen that had obvious yellowing tinting....Im most likely going to return this one as well. My pics on final print are looking horrible so far when using the imac

 

[isuandrew]

Where's that huge thread? I couldn't fint it.

http://discussions.apple.com/thread.jspa?threadID=1093045&tstart=0

my monitor has this problem too, I could see why people might not notice it at first, but being a person who works with photos and color correcting I noticed it the first time I turned my computer on (yesterday)

I need to do color sensitive work with this computer which was the whole reason I got the 24 inch instead of the 20 inch (it 'should' be a better monitor)

I understand that these monitors are not the best for color work, but this is horrible, I can find older imacs with much better displays as well as cheaper LCD screens without any major problem like this. You should get what you pay for, and as a first time mac buyer, they have fell very short when it comes to this monitor.

Has anyone heard anything from apple acknowledging this problem or planing to someday correct it? With all of the graphics/photo/movie people and who ever else uses mac for these specific uses I would think apple wouldn't ignore this issue.

 

[SaSaSushi]

Has anyone heard anything from apple acknowledging this problem or planing to someday correct it? With all of the graphics/photo/movie people and who ever else uses mac for these specific uses I would think apple wouldn't ignore this issue.

You'd think, right?? Now consider the fact that if it was a confirmed problem Apple wouldn't have the luxury of not acknowledging it.

I thought this thread was mercifully dead.

 

[rmwebs]

Today I found that there was a line going all the way from top to bottom of my screen on the left (if you were to divide the screen into 4 segments, it would be on the right side of the left segment). It is only visible on grey/dark backgrounds.

When I came here to see if anyone else had the problem I noticed this thread, and did the background test. Sure enough, I also have the magenta/yellow tinge. 2 problems in one!

I'll be phoning apple care in the morning. Does anyone have any idea what the procedure is? Do they swap out the screen? If so, how long does it take to get the mac back?

Thanks


A great ending to 2007


EDIT: I've just noticed the line is where the edge of my browser goes. Looks like its burnt the line and shadow into the display. Can this be fixed without having to be replaced?

 

[DiamondMac]

Havent had this issue

 

[Digital Skunk]

Interesting enough. My father's HP computer had an HP monitor with the same problems that other are supposedly having with their iMacs. The backlighting was off on the edges and very dim in the center. It wasn't bad when there was anything other than a solid color on the screen, like everyone with broken iMacs are showing us.

I don't think this issue is isolated if it is occurring, and I don't think it's a wide spread phenomena since i have seen good looking HP displays and I have an immaculate 24" iMac sitting in the other room.

 

[tobloyd]

Solution

I think I realised a solution to the problem.

The problem, as I see it:

a great number of the screens have brightness and/or colour distortion. It is more severe on some machines than others and some people are more sensitive to it than others.

A solution:

A simple background compensation utility. It would let the user manually calibrate the screen in red, green, and blue channels. the user would choose a channel and define horizontal and vertical partial-gradients over hot areas of the screen. That way we could calibrate our screens to the darkest spots in each colour channel. The screen would end up dimmer but at least it would be even -- and we could compensate for much of the dimness by increasing the brightness slider (few 'graphics people' would run their screens at full brightness anyhow).

Since OS X has total control over every pixel displayed, this should be a simple, small application to write. It's just too bad that I'm not nearly smart enough to know where to begin!

Now, if some of you smart people reading this know how, please, please get to it cause I also don't want to return my Mac.

Cheers