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Interpolated Resolution
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Sep 10, 2007, 09:19 AM

I know this probably steps on resolution independence, which is something we can obviously expect with the soon coming Leopard.

However, I was just wondering if there was a way to force a higher than standard interpolated resolution in Tiger?

I've noticed that it's given as a standard option when connecting an external display (such as a television) via the DVI output, since I can get HD resolutions on my CRT television (which it certainly doesn't support natively). So, why not on the internal display, too?

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Sep 10, 2007, 09:45 AM
It's currently physically impossible to force a higher resolution than what is native on an LCD.

LCDs work by using millions of tiny transistors. Each transistor is one pixel, and is composed of red, green, and blue subpixels. The transistors are used to display colors correctly - all three on would make white, etc. This is why high-resolution laptop displays cost more - upgrading a WXGA display (1280x800) to WSXGA+ (1680x1050) adds extra $$ to the cost of a machine, because it involves fitting more transistors into the same physical area.

I actually had a Linux distro choke on me, and try to display 1600x1200 on my 1280x1024 17" LCD. The display looked "sparkly" and was moving constantly, because each transistor was trying to display more than one pixel simultaneously, which is impossible - so each was switching between pixels in an effort to compensate. It wasn't nice looking at all.

CRTs display images differently, which is likely why there is some kind of "interpolated" setting in your display control panel when you're connected to a TV. My guess is, though, that you still can't force an image that's higher resolution than what your TV's maximum resolution is...
onlyone-jc  (op)
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Sep 10, 2007, 10:36 AM
Thanks, shifuimam.

So, would I be right in thinking that LCD displays have a fixed pixel density, but CRT displays don't? So, although the resolution being sent to the TV isn't changing, the pix density is being changed, thus emulating a higher resolution?

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Sep 10, 2007, 11:44 AM
CRTs do have a fixed maximum number of pixels. On monochrome CRTs, it's a bandwidth limit, forcing a maximum number of pixels per screen. On color CRTs, there is a maximum for both horizontal and vertical.

CRTs are more forgiving of overdriving, they usually display the image. But you don't get any more detail than the maximum it can display. Set the resolution too high, and the picture gets fuzzy when you look close.
onlyone-jc  (op)
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Sep 10, 2007, 12:20 PM
Thanks, reader50.

My TV has a maximum native resolution of 1024x768, yet I can achieve higher resolutions than this through the interpolation options OS X gives me when I have it connected.

Forcing a non-interpolated resolution any higher than its native point of 1024x768 will make the TV look scrambled and scan-lines will show that the CRT is struggling to achieve what it's being given.

However, with the interpolated resolutions, it's absolutely fine. My understanding of this, is that the interpolated resolutions are emulated via software, but sent out at a lower resolution that is native and supported by the connected display. So, surely if this is possible with a TV, shouldn't it be possible with an LCD, since it's not having to physically change anything due to all the interpolation being generated by the GPU/OS X?

Maybe I'm just understanding it all wrong...

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Sep 10, 2007, 01:29 PM
Hi onlyone-jc -

As I understand it, the method you're describing just down-scales the higher resolution to one that your TV can support (1024x768 in your case). So whilst the Mac may render the screen at a higher resolution (say 1680x1050), it'll be reduced to 1024x76 before being sent to the TV[1].

This doesn't really give you a higher res - detail is discarded before being sent to your screen. It's really no different from scaling an image in Photoshop - pixels are lost as the image is reduced in size.

Generally, sending a signal in the 'native' resolution of your screen is the best option.

[1] LCDs operate slightly differently, I believe: many have up/downscalers that will transform any signal (PVR or games console, for example) into the 'native' resolution of the scren.
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Oct 29, 2007, 12:52 PM

I have a somehow similar issue here, although it looks like it's exactly the opposite. I have an WSXGA+ ViewSonic TFT (1680x1050 native) and I am trying to connect it to my Intel MacMini through a VGA cable. It seems impossible to access the monitor's native resolution, there is no such combination under Display's Preferences list.

I have also tried cscreen (a command line utility able to switch to various resolutions), to no avail. Is there a way to come back to seeing things as they are supposed to? I am looking at everything somehow stretched right now...
When connected through DVI, everything works just fine at 1680x1050.

Thank you in advance.
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