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Mac Forum / General / Hardware / October 2007iMac display
My new 20-inch iMac arrived on Tuesday, and there is a definite problem with the display. I had wondered if it was an issue with all machines, but I checked one in a store, and wasn't able to reproduce the problem. Obivously I can (and will) contact AppleCare. I hope I won't have to send the machine back or even take it into an AppleStore (which isn't easy living in London). Generally I reckon the combined expertise of people on the newsgroups makes them a better resource than AppleCare if no actual care is needed. The problem is a very noticable change of colour depending on the angle I look at the creen. I know colours depend on angle of view to some extent, but as I said I was not able to reproduce this when looking at a different machine. Currently I am sitting at the computer, typing this message into a white window. I have a Finder window open which is perhaps (not sure) a slightly different shade of white and also a mostly white Safari window. When I stand up and look down at the screen from above I see that the window I am typing into remains white, but the Finder window and the white areas of the Safari window take on a shade of purple. When I look at the screen from my seated height but from far left, the typing window takes on a gold colour as do the Finder window bars. When I look from far right I get similar but slightly different effects. So is this something that will go away after the machine has been used for a while, something that just needs a simple tweak, something that has to be lived with (which I could do at a pinch but don't want to do) or is a repair needed?  Signaturehttp://www.decohen.com Send e-mail to the Reply-To address; mail to the From address is never read This seems to be a fault in the new iMacs, and if you check any of the Mac forums you will find lots and lots of complaints about the dark to light shading as you go down the screen. My iMac does it, and it is annoying - for anyone working with colours though it is a ReAL problem. At present it seems Apple are denying it is a endemic fault, but by the number of people returning their iMacs because of this fault I (and many others) are hoping for a recall and fix But since i use my iMac for email, word processing , surfing etc and have no need for accurate colour rendition I will keep my iMac whether or not they do a fix Apart from this and the crappy new mouse I luv my Mac David > My new 20-inch iMac arrived on Tuesday, and there is a definite problem > with the display. I had wondered if it was an issue with all machines, [quoted text clipped - 26 lines] > has to be lived with (which I could do at a pinch but don't want to do) > or is a repair needed? > This seems to be a fault in the new iMacs, and if you check any of the > Mac forums you will find lots and lots of complaints about the dark to [quoted text clipped - 18 lines] > > with the display. I had wondered if it was an issue with all machines, > > but I checked one in a store, and wasn't able to reproduce the problem. Yes, I had heard of a "gradient" problem. And what I get 'could' be this in its form when the main colour is white. But it definitely depends not on where the item looked at is located on the screen, but where it is in relation to the user. Now that I look directly at the screen I can *also* see that the top is darker than the bottom. Signaturehttp://www.decohen.com Send e-mail to the Reply-To address; mail to the From address is never read >> This seems to be a fault in the new iMacs, and if you check any of the >> Mac forums you will find lots and lots of complaints about the dark to [quoted text clipped - 27 lines] > Now that I look directly at the screen I can *also* see that the top is > darker than the bottom. The top of the screen appears darker because of your viewing position. Pull the top of the display towards you or move your body until your eyes are at the same level as the top of the screen. I see the same artifacts as David described. I don't believe my display is defective. The display can be swiveled up or down to minimize the idiosyncrasy. When viewing the screen from above, the whites change to blue and gray becomes dim white. When viewing from narrow side angles the grays appear bronze. There is no difference between left and right narrow angle viewing. > The top of the screen appears darker because of your viewing position. > Pull the top of the display towards you or move your body until your [quoted text clipped - 8 lines] > appear bronze. There is no difference between left and right narrow > angle viewing. If the display isn't defective I guess I can live with it, as it's the most convenient Mac in terms of specs and price. I get precisely what you describe (better desscription than mine) but after all, for more than 90% of the time I am directly in front of the machine with no-one else viewing. I might not even have noticed the situation if I had never had the machine on while sitting down. But I want to check further, as my one test of another iMac did not seem to have the problem. Signaturehttp://www.decohen.com Send e-mail to the Reply-To address; mail to the From address is never read >> This seems to be a fault in the new iMacs, and if you check any of the >> Mac forums you will find lots and lots of complaints about the dark to [quoted text clipped - 27 lines] > Now that I look directly at the screen I can *also* see that the top is > darker than the bottom. Does this mean that the new iMac uses cheaper TN panels for its display? TN panels are characterized by poor viewing angles and less color support but have faster response times. Could explain what you are seeing... Chris > Does this mean that the new iMac uses cheaper TN panels for its display? TN > panels are characterized by poor viewing angles and less color support but > have faster response times. Could explain what you are seeing... > > Chris The 20 inch iMacs have sucky TN displays. The 24 inch iMacs have something better, whether its PVA, TVA, or S-IPS is unknown to me. If you have the money buy the 24 inch instead and don't even think about it. You get a better display with viewing angles good enough to use as a tv and its big enough for 1080 HD content. I didn't have enough money and bought a 20 incher. If I set it up as a tv at most 2 of the 3 sitting positions on the couch can view it the image. The sound quality isn't as good as my 20 y/o KEFC30s, but its pretty good considering its a computer and the speakers are firing downward. The internal amp is speced at 25 watts and the speakers are loud enough, which makes me believe that they are using a Class D amp. > The 20 inch iMacs have sucky TN displays. The 24 inch iMacs have > something better, whether its PVA, TVA, or S-IPS is unknown to me. If > you have the money buy the 24 inch instead and don't even think about > it. You get a better display with viewing angles good enough to use as a > tv and its big enough for 1080 HD content. I didn't have enough money > and bought a 20 incher. Not the money, but I don't want the extra size, and would not want to use it as a TV. I already find that the 20-inch is in some ways not as conveient as my previous 19-inch (external for a PowerBook). Because the 20-inch is significantly wider and not as deep. If my machine isn't individaully faulty I guess I'll live with it. It's a hassle to take it in to be checked (in London cars are more trouble than they are worth, and I don't have one). On the other han, if enough of us complain to Apple, they might acknowledge that some machines have a display that is worse than normal and needs fixing/replacing. Signaturehttp://www.decohen.com Send e-mail to the Reply-To address; mail to the From address is never read >> The 20 inch iMacs have sucky TN displays. The 24 inch iMacs have >> something better, whether its PVA, TVA, or S-IPS is unknown to me. If [quoted text clipped - 16 lines] > acknowledge that some machines have a display that is worse than normal > and needs fixing/replacing. This may be an interesting read: http://blogs.chron.com/techblog/archives/2007/09/an_imac_display_dilemma_20inch_ value_or_24inc.html from that it looks like the 24" is a PVA while the 20" is indeed a TN. A lot of people that bought 20" models obviously did not know (the info is hard to find and not mentioned by Apple at all in the product description), did not expect it and now are complaining about it. Not a nice way to treat your loyal customers, I think. I know this thing about TN displays by chance because recently I have not been able to buy ANY laptop that has not that awful TN display. The previous Macbook Pro also had it. And when I asked about it in the Apple shops, they told me not to worry and showed me the setting where it says "millions of colors". An 18-bit TN display is only capable of 262.144 colors while a 24-bit PVA panel is capable of 16.777.216 colors. Chris >>> The 20 inch iMacs have sucky TN displays. The 24 inch iMacs have >>> something better, whether its PVA, TVA, or S-IPS is unknown to me. If [quoted text clipped - 18 lines] > This may be an interesting read: > http://blogs.chron.com/techblog/archives/2007/09/an_imac_display_dilemma_20inch_ value_or_24inc.html from > that it looks like the 24" is a PVA while the 20" is indeed a TN. A lot > of people that bought 20" models obviously did not know (the info is hard [quoted text clipped - 11 lines] > > Chris The specs do show more brightness and a wider viewing angle for the 24" model <http://www.apple.com/ca/imac/specs.html> but they definitely don't emphasize it. Hi Chris It seems as if you are saying the TN displays cannot be set to millions of colours - if so then I think you may be mistaken as my 20 inch iMac, with the lousy screen, is set at millions of colours. David >... > [quoted text clipped - 6 lines] > > Chris > Hi Chris > > It seems as if you are saying the TN displays cannot be set to millions > of colours - if so then I think you may be mistaken as my 20 inch iMac, > with the lousy screen, is set at millions of colours. AIUI, this is done by dithering, whereas the better screens actually display that number of colours. I am told you can tell the difference by seeing if it says "millions of colours" or the more specific "26 million colours" - the 26 may well not be accurate, the point is naming a specific number. Signaturehttp://www.decohen.com Send e-mail to the Reply-To address; mail to the From address is never read > > I know this thing about TN displays by chance because recently I have not > > been able to buy ANY laptop that has not that awful TN display. The [quoted text clipped - 6 lines] > of colours - if so then I think you may be mistaken as my 20 inch iMac, > with the lousy screen, is set at millions of colours. The computer can be set to millions of colours (24-bit colour), and its video hardware will actually generate that many distinct colours, but the screen can't display that many and will only be able to directly display colour with 18-bit resolution. In effect, the TN display is throwing away 6 bits of colour information (2 lowest order bits each for red, green and blue). The screen compensates somewhat by using a dithering technique: in an area where a constant colour has been used, and that colour cannot be represented directly (i.e. the low order 2 bits are not zero for any primary colour), it will alterate pixels between the two nearest colours, so on averge a large area of pixels will be the correct colour. You will be able to see patterning effects if you look closely enough. The technique doesn't work as well for regions of variable colour. SignatureDavid Empson dempson@actrix.gen.nz Right, I understand now thanks. But out of curiosity how do you find out this sort of stuff? Books? Uni? David > > It seems as if you are saying the TN displays cannot be set to millions > > of colours - if so then I think you may be mistaken as my 20 inch iMac, [quoted text clipped - 16 lines] > You will be able to see patterning effects if you look closely enough. > The technique doesn't work as well for regions of variable colour. > Right, I understand now thanks. But out of curiosity how do you find > out this sort of stuff? Books? Uni? > > David wikipedia can already give you that much information: http://en.wikipedia.org/wiki/Thin_film_transistor_liquid_crystal_display but you need a reason to search for it in the first place, right? Apple does make sure that there is little suspicion from the buyers of their products. I think that they should include this information in their product description (which they don't) so that we don't have to become some kind of expert in computer display panels before we can buy a computer with piece of mind. Chris .... > wikipedia can already give you that much information: > [quoted text clipped - 8 lines] > > Chris Right Chris Like perhaps many others I didn't actually see one of the new iMacs before mine arrived - I did see one of the white ones at a local dealer however, and as a long time Mac user (since MacPlus days) never dreamed Apple would EVER sell a Mac with a display that was not better than everything else on the market (within reason of course). So just ordered the aluminium iMac (20") and was astonished and dismayed when I saw the poor display. David >as a long time Mac user (since MacPlus days) never dreamed >Apple would EVER sell a Mac with a display that was not better than >everything else on the market (within reason of course). The variable here has always been "within reason". > > [Description of 24-bit vs 18-bit colour and dithering] > > Right, I understand now thanks. But out of curiosity how do you find > out this sort of stuff? Books? Uni? I picked up this particular knowledge through understanding how computer graphics operates (from the programming point of view and as a user), which was learned over many years through experimentation, reading and being taught. I haven't done much work with graphics recently, but back in high school (1980s) I wrote some graphics editing software on the Apple II, and that was almost entirely self taught. I did a graphics course at university but I already knew most of the parts to do with 2D graphics editing. At the same time I was using the Apple IIgs, which uses dithering in some of its graphics modes to display 16 colours with only 2 bits per pixel, so I was familiar with the concept. SignatureDavid Empson dempson@actrix.gen.nz Thanks - a great way to learn cheers David > > > [Description of 24-bit vs 18-bit colour and dithering] > > [quoted text clipped - 14 lines] > some of its graphics modes to display 16 colours with only 2 bits per > pixel, so I was familiar with the concept. |
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