Custom Resolution settings for Mac -> Sharp 37" LCD  

Hello,

I've been struggling with this for a while, and now that I've finally achieved success, I wanted to report my results for anyone else to benefit from.

My mission was to get my PowerBook to drive my Sharp LC-37GD4U at its native resolution. There were three points to this objective: 1) Use the entire screen, 2) Have an unscaled (i.e. "perfect") image, and 3) have the entire image fit on the screen (i.e. no overscan).

The trouble comes from the fact that the native resolution of the panel is 1366x768, but that resolution is not presented as an option by OS X. An interesting side note is that you can connect your DVI output to the DVI input and also with the right cable, the HDMi input. The HDMI input allows a resolution of 1344x756 - very close to native, but no way to fine tune it. The HDMI image will be overscanned - too big for the screen by about an inch all the way around - and it will be scaled, so lots of images will look worse on it than they do on a computer display. The Sharp offers excellent fine tuning capabilities on the DVI input, but absolutely none on the HDMI input.

The DVI input offers 1280x768 - also very close to native, but far enough that it gets scaled. However, along the way I realized that if I set the view mode to "dot by dot" (instead of sidebar, zoom or stretch) - that it does not get scaled, and that with some fine tuning, you can align the signal with the panel for a perfect image. More on that below. But the point is I could have stopped here, having achieved a perfect image and use of 100% of the panel's vertical resolution, and 94% of it's horizontal resolution.

So keep in mind, if you continue here, all you are going to get, beyond going with 1280x768, dot by dot, and fine-tuning, is 86 more pixels. It is worth noting that with the same utility that I used, you could theoretically customize 1344x756 over the HDMI to fit in the screen (not be overscanned), but I didn't put much time into this.

Anyway, the way I got the full resolution was with a utility called SwitchRes X. This allows you to define custom resolution settings beyond those that OS X by default is willing to display, which many moderm Mac video cards will allow. Custom resolutions are quite complicated, with many parameters who's names or implications make little sense to me. Windows users have a utility called PowerStrip which serves the same purpose. It took a while to figure out how to come up with settings that had any chance of being valid. I've written a little SRX Helper-FAQ that explains what little I do know about making valid settings.

As for drving my Sharp LCD at it's native resolution, Here is what works. I would expect this to work equally for the LC-37GD6U, LC-37G4U, and possibly all Sharp LCD's who's native resolution is 1366x768. In particular, these values are probably specific to the Radeon 9200 that is build into my PowerBook, or possibly several of the Radeon series video cars. Note: Don't bother installing ATI's custom drivers. I did, and they didn't provide or enable any different capability.

Pixel Clock*: 74.25 MHz
Value Horizontal Vertical
Active 1360 768
Front Porch 130 0
Sync Width 114 0
Back Porch 40 0
Scan Rate* 45 kHz 58.593 Hz

* Pixel Clock and Scan Rate are intrinsically tied together and are a function of each other and the other values. My FAQ linked above explains as much as I understand about this. Simply put, you do not enter the Scan Rate values (even though the fields are editable). Rather, You enter Pixel Clock first, then all the other values - and both scan rates will be calculated for you.

Note that I'm sacrificing 6 pixels in horizontal resolution - this is the best I could get the OS and video card driver to accept (in other words, it's the closest value set I tried in SRX that actually showed up as selectable). For 6 pixels I was willing to declare victory.

Before you fine tune your TV, do the following on:
Select the DVI input (if you haven't already)
Menu->Setup->Input: Set it to 1366x768
View Mode: Select "dot by dot".

As I mentioned above, once you have the proper resolution, you have to calibrate your display to optimize its appearance. Initially it will probably be scaled slightly and flickering a little. The scaling will make certain types of imagery appear to have bands of varying color, where there should be a consistent color or pattern. If you tell your Sharp to Auto-Sync (Menu->Setup), and you've done the above settings first, it will probably get the resolution alignd correctly, but leave you with some flickering. I wrote up a detailed fine tuning post on the procedure I used to manually align the resolution, and remove the flickering. The test image I used for this procedure is attached.

I tried to attach the test pattern above, but it was rejected because it is 1280x768.

You really want the pattern to cover the entire screen so you can clearly see if there is any artifacting anywhere. So I've uu-encoded the file and loaded it as a text file. Stuffit (or WinZip) should be able to decode it fine, although you may have to strip the ".txt" off of the end.

Moderators - this file is only 4k as in 4000 bytes. Please don't reject it due to it's image size - the image size is necessary to fill a screen, because it is a test pattern.

 

test-pattern.uu.txt 4.3681640625k . file

It didn't show up in the menu, I couldn't select it. It's possible that if I had tweaked some of the minor settings (porch, scan width, etc) that I might have gotten it to work, I don't know.

After so many reboots, it's not hard to suddenly be happy with being 6 pixels shy of perfect.

Yes, the mini is where I'm heading with this as well.

Thom,

VRAM is not an issue. The mini has more than enough VRAM to display 32 bit color simultaneously to a full 1920x1080. It has 32 MB, and that res/color depth takes barely 8 MB. I'm pretty sure extra video memory is only used for 2d/3d acceleration capabilities, and those are only used by software that explicity leverages the appropriate API. I'm pretty sure MPEG decoding doesn't touch it.

The limiting factor in playing HD is sheer processing power. My PB15 w/ 1.5 GHz G4 and PC2700 RAM is just about 5% too slow to decode 1080i mpeg2. Specifically, I used the Sharps' firewire output to record the series premeir of Point Pleasent in HD, over the air (using Apple's sample Virtual Digital VHS app ). It can record & replay the HD stream without skipping a beat (14% cpu). But to actually *decode* the stream and render it, it's pretty jumpy. My PB drives the Sharp magnificently. I'm going to get a mini too, to play back ripped DVD's, and to receive and play TiVo transfers once my TiVo's get upgraded with TiVo2Go capability.

No, I don't have any elgato products.

The only thing you can possibly play back through the firewire cable is an HD mpeg2 stream that has been recorded, not necessarily by the D-VHS app, but I doubt you have anything else that will get such a stream to your disk.

So, you need to solve the device not showing up problem first. The order you connect things is significant, I think D-VHS has to be running before you connect the firewire cable, then you go to iLink on the TV. But I may have that backwards, it may be that firewire has to be connected before you launch D-VHS.

Anyway, yeah, there's a whole thread about this, I linked to it above.

A simpler way to think about it is this: If it is a High Definition source, then yes, the TV can output it over the firewire. It doesn't matter if it's cable high def or over-the-air high def, the answer is yes.

Technically I should have said "if it is a DTV source" b/c 480p counts too. I just didn't want to confuse people who don't understand that "digital cable" is not the same as "DTV."

The difference to keep in mind is this: If the TV's decoder is processing the digital signal, then it can also send a copy of that signal out the firewire port. If you have to set the TV to the actual channel you want to watch, and that channel has a decimal point in it, then it's digital. If you have to set the TV to analog chanel 3 or 4 so the cable box can decode, then the TV has no mpeg stream to copy to the firewire. Likewise if you're using composite, s-video or component, those are analog signals, so no dice. Finally if you're using HDMI or DVI input to the TV, they may be digital, but they are not MPEG2. There is no standard for sending a DVI signal over firewire, it wouldn't fit.

so yes, you can output the OTA HD source, but I think we've already covered that.

As for your cable company, it is possible that you don't need their box at all. I never ordered HD, I just put a splitter on the coax before plugging it into the analog antenna jack, and then plugged it also into the digital antenna jack as well. Then told the TV to go do it's channel discovery. There are a few different formats they can use, I tried them all, and the last one worked. I got 3 of the 5 HD channels they carry, all ones they pick up OTA themselves. The other two, Discovery and ESPN, I did not get. I don't know what's special about them or why my TV couldn't find them. I didn't spend much time looking into it.

Hey Thom,

I'm sorry you're having so much trouble - believe me, it was just as frustrating for me.

Yes, the difference in the display cards would explain why one would work but not another.

As for the changing values, it could be that SRX is forcing your values to be divisible by 4. SRX does that with the resolution itself, but I didn't think it did it with all of the other timings. I'm actually running a one-off version of the SRX control that doesn't do that, to test it for the author. I think he plans on including it in a future update. However, I wouldn't expect a difference of 2 pixels to be a deal breaker.

One thing you have to keep reminding yourself of is that you can get 1280x768 without all of this custom resolution frustration, and it is only 80 pixels narrower than if you do get all this to work. I told myself over & over again to let it go & stop wasting my time, but somehow I couldn't let it go.

As for modifying the menu, the author of SRX told me that in some cases just logging out & logging back in is good enough. The trouble is that there are only certain times when OS X reads the file, and the author hasn't found a way to force it to do so. Yes, it's frustrating.

That main display thing happened with me too, I never did figure it out. You're doing this with a power book though, right? You can switch all of this stuff with the context-menu; control-click on the desktop on either display, and you get sub-menus that can change resolutions on either one, and switch the menu bar. As long as you have one working display, you shouldn't need to remote in.

I also did have a case of a resolution working, and then failing to work later; 1344x756 which is what the HDMI input negotiates. I tried it on the DVI and it worked. But at some point it stopped working, and I never did get it back. But that is partly b/c when I got 1360x768 working, I stopped trying for the others.

Hello Everyone,

Now that I have my mini hooked up, I've been able to determine custom resolution settings for SwitchRes X that enable it to drive my Sharp 37" LCD panel at 1360x768.

Here they are:

pixel clock: 81 MHz
parameter horiz vert
pixels 1360 768
front porch 48 1
sync width 248 30
back porch 112 3

scan rate 45.814 57.125

As before, scan rates are computed for you, you don't set them. See the rest of the thread regarding my procedure for how to fine-tune your display for optimum picture synchronization (pixel alignment, scaling avoidance, and flicker reduction).

deleting this post, erroneous

SandMan,

It's not knowledge of SRX that you need, it is knowledge of working values for your existing setup. You need to find out what settings the built-in resolutions are using, and then tweak from there, by adjusting front & back porch, etc, to tune out the overscan issue.

However, there is no simple answer for how to find out what the existing settings are. I believe the author of SRX has developed the ability to show you the values of existing resolutions, but AFAIK, he hasn't included it in a public version of his product yet. I highly recommend you email him and ask when he plans to do that, and if he'd be willing to let you try a development version with that functionality.

In theory, you could develop custom settings from scratch, but you would need to know a LOT more about display technology than I do, and you would probably also need detailed internal specifications of both your TV and your video card, neither of which are likely to be publicly available.