 |
powerusers.info
Power Tools for Power Users!
|
| View previous topic :: View next topic |
| Author |
Message |
Merlin
Site Admin
Joined: 29 Jan 2004
Posts: 722
|
 Posted: Wed Mar 24, 2004 9:15 pm Post subject: |
 |
|
| Do you notice the blurriness I was referring to when you do it (what I mentioned above)? |
|
| Back to top |
|
 |
RIP
Advanced Systems Administrator
Joined: 17 Mar 2004
Posts: 113
Location: Resting In Peace
|
| Posted: Wed Mar 24, 2004 9:51 pm Post subject: |
|
|
| ped wrote: | | But the same effect happens in games. It's an issue of the pixels on an LCD panel not being able to switch colors quickly enough. |
If it is a color issue how come it does it on some things that are black and white and not on others?
not being an ass, I just don't understand... |
|
| Back to top |
|
|
Merlin
Site Admin
Joined: 29 Jan 2004
Posts: 722
|
| Posted: Thu Mar 25, 2004 7:22 am Post subject: |
|
|
I'm not sure I've ever seen it NOT do it. Sure the effect may be more pronounced in one situation than another, but that's likely due to what colors are being changed from and to. Take for instance a common panel today. Most have a pixel response rate of 25ms (equivalent to a refresh rate on a CRT). If you take the total number of milliseconds in a second (1000) and divide that by 25 you get:
40
Which means that even under the very best of circumstances you can't paint more than 40 frames per second on this LCD screen.
That's why your games and other fast-moving items have blurriness; your videocard can probably render at 60-120 frames per second but your LCD holds it way back. |
|
| Back to top |
|
|
Xmaniac
Power User!
Joined: 05 Feb 2004
Posts: 637
Location: MI
|
| Posted: Thu Mar 25, 2004 12:26 pm Post subject: |
|
|
| ped wrote: | | Do you notice the blurriness I was referring to when you do it (what I mentioned above)? |
well I havnt played Games on a LCD yet, but just moving the mouse on one I can tell. |
|
| Back to top |
|
|
RIP
Advanced Systems Administrator
Joined: 17 Mar 2004
Posts: 113
Location: Resting In Peace
|
| Posted: Fri Mar 26, 2004 12:10 am Post subject: |
|
|
| Quote: | | With today's LCDs, a total response time of close to 30 milliseconds (ms) can be achieved, virtually eliminating ghosting and image trailing from video applications. Sometimes this specification is shown in halves to show the twist, then the untwist time. The full range should be considered, however, to fully determine the display's ability to accurately show full-motion video. |
Taken from the tail end of this report...
http://www.necmitsubishi.com/support/css/monitortechguide/index04.htm
Could be an ad for LCD's? |
|
| Back to top |
|
|
RIP
Advanced Systems Administrator
Joined: 17 Mar 2004
Posts: 113
Location: Resting In Peace
|
| Posted: Fri Mar 26, 2004 12:18 am Post subject: |
|
|
I found a test rate on mine, it says that they too had a hard time finding it posted by the manufacturer, but ran tests and got these results, with an average response time of 24ms...
I have no clue what these mean.. :)
Pixel Rise Time
Pixel Fall time
 |
|
| Back to top |
|
|
Merlin
Site Admin
Joined: 29 Jan 2004
Posts: 722
|
| Posted: Fri Mar 26, 2004 7:22 am Post subject: |
|
|
| RIP wrote: | | Quote: | | With today's LCDs, a total response time of close to 30 milliseconds (ms) can be achieved, virtually eliminating ghosting and image trailing from video applications. Sometimes this specification is shown in halves to show the twist, then the untwist time. The full range should be considered, however, to fully determine the display's ability to accurately show full-motion video. |
Taken from the tail end of this report...
http://www.necmitsubishi.com/support/css/monitortechguide/index04.htm
Could be an ad for LCD's? |
Maybe so - note the "virtually". As I showed above a pixel response rate of 25ms only translates into 40 fps. That's not fast enough, in my book. I jack my games to 120Hz or above at 1024x768 on my CRTs, so I have 3 times the refresh rate of one of those LCDs at 25ms. |
|
| Back to top |
|
|
Merlin
Site Admin
Joined: 29 Jan 2004
Posts: 722
|
| Posted: Fri Mar 26, 2004 7:24 am Post subject: |
|
|
| RIP wrote: | I found a test rate on mine, it says that they too had a hard time finding it posted by the manufacturer, but ran tests and got these results, with an average response time of 24ms...
I have no clue what these mean.. :)
Pixel Rise Time
Pixel Fall time
|
Hehe I think "rise" means to turn on an individual pixel with a certain color, and "fall" is to turn off an individual pixel. And they're showing along the bottom the amount of time it takes. So it appears that the panel they were testing took about 18ms to turn on a pixel and about 23 to turn it back off if I'm reading that right. |
|
| Back to top |
|
|
RIP
Advanced Systems Administrator
Joined: 17 Mar 2004
Posts: 113
Location: Resting In Peace
|
| Posted: Fri Mar 26, 2004 8:35 am Post subject: |
|
|
and lower is better, correct?
This was their test on the Samsung 192N, the one I am using...
They tested most of them at www.xbitlabs.com, the only thing they said bad about mine that I saw was that it was over priced... THis was the one my Fiance really wanted so we went with it...
She also picked out and really wanted our WideScreen HTDV big screen TV and our 6.1 surround sound... How cool is that??? :D |
|
| Back to top |
|
|
Lefty
Power User!
Joined: 30 Jan 2004
Posts: 233
Location: MD
|
| Posted: Fri Mar 26, 2004 9:45 am Post subject: |
|
|
cool! imagine what you'll get when your married  |
|
| Back to top |
|
|
Merlin
Site Admin
Joined: 29 Jan 2004
Posts: 722
|
| Posted: Fri Mar 26, 2004 4:32 pm Post subject: |
|
|
| RIP wrote: | and lower is better, correct?
This was their test on the Samsung 192N, the one I am using...
|
Lower is better. But, as noted, LCDs aren't very fast and that one isn't, either. It's not going to do better than 55 fps or so it seems. Best case is 18ms to turn on a pixel:
1000/18 = 55 fps. |
|
| Back to top |
|
|
cowdog
Newbie
Joined: 18 Mar 2004
Posts: 12
|
| Posted: Tue Mar 30, 2004 2:15 pm Post subject: hmmm |
|
|
interesting looking over this...
When I had MOHAA on my Mac, my fps was always over 120... i never noticed any blur in movement, but it never seemed quite as sharp on the edges of models as a CRT would have been... but I felt the LCD was an improvement overall.
To me, the LCD seemed easier to look at than a CRT, but after talking to pros using Maya, I changed my mind. Every one claimed an LCD hurt their eyes due to lower refresh rate.
Those looking intently and CLOSELY at screens for long periods of time (Maya application) all claimed they preferred a CRT.
just my 2 cents
_________________
~£Å~Çowdog |
|
| Back to top |
|
|
Merlin
Site Admin
Joined: 29 Jan 2004
Posts: 722
|
| Posted: Tue Mar 30, 2004 5:51 pm Post subject: |
|
|
| When you're seeing 120 fps on an LCD that simply means you've got vsync disabled. And when you have vsync disabled you're not really getting 120 fps (or whatever your game tells you you're getting). If you care about why this is reply and I'll go into detail. |
|
| Back to top |
|
|
RIP
Advanced Systems Administrator
Joined: 17 Mar 2004
Posts: 113
Location: Resting In Peace
|
| Posted: Tue Mar 30, 2004 6:45 pm Post subject: |
|
|
I do... :)
My frame rates vary but I have seen higher than that as well...
and where the heck do I go to enable it, I went through every freaking tab I could find... |
|
| Back to top |
|
|
Merlin
Site Admin
Joined: 29 Jan 2004
Posts: 722
|
| Posted: Tue Mar 30, 2004 8:48 pm Post subject: |
|
|
OK well you're all familiar with the concept of video memory, right? This is just RAM like your CPU uses but onboard the videocard. There is a special area of that memory that directly corresponds to what you're seeing on the screen at all times. This is sometimes referred to as a 'framebuffer'. Every pixel on the screen has a corresponding piece of this memory. And the amount of the memory needed for each pixel is a function of 'pixel depth' (also called 'color depth'). An example helps to clarify this:
Say you're running a 1024x768 screen at 24 bit color. A 'bit' is a simple 0 or a 1. A 'byte' is 8 bits strung together. So 24 bits is the same thing as 3 bytes. So if we want to see how much memory this screen at 1024x768x24 (bits per pixel) takes up, we can simply multiply:
That's the number of pixels on the screen at this resolution. Now we multiple that number of pixels by the amount of memory per pixel (24 bits, or 3 bytes - we'll use bytes since we'll be wanting the result in KB or MB):
| Code: | | 786432 x 3 = 2,359,296 bytes |
So our screen is using a little over 2 MB of memory at this color depth and resolution (exactly 2 MB is 2,097,152 bytes).
Now, knowing how much memory is used, anytime the videocard driver writes to this mapped area of memory "instantly" (the quotes will be understood later) the image on the screen changes to reflect that new changed value. IOW, changes to this memory area are all that is required to immediately change what is seen on the screen.
Now in addition to this main framebuffer that directly corresponds to what's on the screen, the videocard has more memory. This is for holding textures and things for sure, but is also used to build subsequent frames out of view. So in our above example we used about 2 MB of video memory for our current display. In games and other media applications for best performance our video drivers will build frames after the one being currently displayed in another identically-sized area of memory (another framebuffer). You've probably heard of "double" or "triple buffering"? This is what they're referring to - the building of new frames to be displayed while the current one is still being displayed. When they're done and the videocard is ready, the next frame thus drawn is copied intact from its current memory location to the one that correponds to what's being seen by the user. This is usually called page-flipping, and simply means that the frame has been updated from one picture to another. Think of this drawing of frames offscreen, and the subsequent moving them to be viewed as analogous to an old Disney cel animator - they would draw subsequent frames of animation on super-thin onion-skin paper. And if you flipped through the pages you'd see the animation play back (in rough form). This is the same way your computer creates motion - playing back still images in rapid succession.
Now that we know all of that about videocards and memory we now need to understand how monitors display an image. We'll only be dealing with the traditional monitor form, a CRT (tube monitor with electron guns). In this type of monitor there is a glass tube with either of two main technologies for displaying an image. The first is known as "shadow mask" and is composed of a plastic or metal flat inner surface puntuated by holes at various intervals. The holes are arranged in what are called 'triads', which are groupings of red, green, and blue elements. Together one triad makes up a single pixel. The electrons from the electron gun pass through the holes in the plastic face (the "mask") and excite the inner phospor coating on the inside of the tube, which then glows a corresponding brightness of red green and blue to create the various colors we see onscreen. The second type seen is the "aperture grill" ("Trinitron") type of CRT. This kind doesn't use holes in a plastic or metal sheet; it instead uses a series of suspended metal wires that are suspended at the front of the display, from top to bottom. These tiny wires are held in place by one or two horizontal wires which will be faintly seen in the bottom and top 1/3rd of the screen. The same concept applies here in that an electron gun fires through this mesh of wires and excites the phospors and triads on the screen.
Knowing the two types of monitors is useful but not absolutely necessary for this discussion. The part that we do need to know is how the monitor paints the image onto the screen. The electron gun referred to above paints the image from top to bottom, left to right, a line at a time. So it starts at (your) top-left of the screen... paints the very top line of pixels... then turns off and moves to the beginning of the second line... then turns on and paints that line, etc until it gets to the last line on the screen. The time it takes for it to do this is called "refresh rate" and is the indicator that tells how many times per second this process can occur. Refresh rate is a function of both your monitor and your videocard. You typically should choose the fastest refresh rate supported by your videocard that is also displayable by your monitor, as it's much easier on your eyes. now when the electron gun hits the last line of the display and paints that very last line, the gun turns off again, and must now retarget itself from the bottom-right of the screen all the way back up to the top-left, where it will start the next frame. This time interval while it's off and travelling that distance is known as the 'vertical blanking interval'. It is this item that is key to understanding why those 120+ frame rates (or more -I hear people talk of 200-500 fps frame rates often, especially in BZ) you're seeing are bogus rates.
IMPORTANT - If you have vsync ENABLED on your card's properties you are stating that you do not want the videocard to swap framebuffers (between what's being seen now and the next frame being rendered) anytime except during the vertical blanking interval (when the full frame has just been painted, and the electron gun is off, and heading back for the top of the screen).
If you have vsync DISABLED you are telling the videocard driver that it can update the primary display framebuffer (the one you're seeing) anytime it likes (IOW as fast as it can).
Can you see the problem already? The problem is that with vsync disabled your videocard and monitor are, at best, out of sync with each other. The monitor plugs along at whatever refresh rate it's set to (let's say 85 Hz - that's 85 times per second), and the videocard is rendering frames as fast as it can, which in some parts of the game could be as fast as 120-150 frames a second and, when the action is hot and heavy, may be as slow as 15-30 frames a second. Why is this bad? A better question is why is this good? IOW why would you WANT your monitor and videocard out of sync with each other? The only real benefit here is that you'll never keep the videocard waiting for anything; it can render as fast as it wants to without regard to what's on the screen. This is a nebulous benefit because *no matter how fast your videocard is, you can't see more frames per second than your monitor can draw*. What's that you say? If my videocard is rendering 255 frames a second isn't that what I'm seeing? No it isn't. Let's say we're stilll at an 85Hz refresh rate with vsync disabled, and we're indeed seeing a frame counter in our game that's showing 255 frames per second (fps). Let's examine what's happening here to see why this is bogus:
For the purposes of this little thought experiment I'm going to assume that both the monitor and the videocard are at the beginning of a frame - that is, the monitor has the electron gun positioned at the top-left about to turn on to draw the first line of the screen (at a refresh rate of 85Hz), and the videocard is about to swap in a new frame to the primary buffer (at a steady rate of 255 fps). Now the videocard swaps the next frame into the primary display buffer and the monitor begins painting lines on the screen. By the time the monitor has painted the first 1/3 of the lines on the screen, the videocard is ready to swap in the next frame of the game action (at 255 fps it's rendering exactly 3 times faster than the monitor is refreshing 255/85 = 3) and does so. So at the 1/3 point on the screen (from the electron gun's perspective in the monitor) the videocard swaps the next frame into the primary memory buffer. Now the monitor carries on (still drawing the same first frame from its perspective since it's always drawing whatever is in the primary buffer) and continues painting lines. The monitor is still drawing what's in the primary buffer, only now *the primary buffer's contents have changed* and the positions of objects (depending on the game action, movement, changes in lighting, gunfire, etc) are different than they were during the first 1/3rd of the screen. Let's continue. By the time the monitor has painted the second third of the display the videocard is ready to swap in yet another frame to the primary buffer and does so. Now the monitor continues painting the bottom third of the screen's lines, doing so now with the corresponding contents of yet a *third* frame of animation. What this all means in the end is that we have one picture painted to the monitor screen surface, but it's composed of *3 completely different images, being sectioned into 1/3 of the screen each*. So we got the top 1/3rd of the screen from frame 1, the second third from frame 2, and the last third from frame 3. Imagine if there was a lot of action going on in the game how this can mess up the image you're seeing on the screen. The more out of sync the monitor and videocard get in terms of update speed the worse this effect becomes. You can easily see the effect on vertical lines if you move your view in a 3D game from side to side rapidly. What you'll see is jagged lines running down what should be smooth vertical lines that make up the edges of buildings or poles, etc. This is because of what we just described above - each frame in the game is simply a snapshot in time of what was happening when the frame was rendered. Because you're moving rapidly from side to side the position of the vertical lines that make up the objects in the game were in new positions when that frame was rendered, and since we're updating the primary buffer (the one seen onscreen all the time) without regard to where the monitor is in its drawing sequence, we end up seeing multiple positions for the same objects on the screen. The ultimate example of this that demonstrates the problem is to imagine a monitor having a 1 Hz refresh rate (that is the monitor is set to scan only ONE frame per second. So it takes a full second for it to draw all the lines from top to bottom and reset the electron gun back to the top line. Now further imagine that we have a videocard that can render 100 fps steady at the current settings and is doing so, with vsync disabled. What will you be seeing onscreen? You'll see *one hundred horizontal slices of 100 different frames, representing 100 different timeslices of a full second of gameplay*. IOW a mess.
With vsync ENABLED the videocard can work on background frames (double or triple buffers) but cannot update the primary buffer until the next vertical blanking interval. When the next vertical blanking interval occurs the primary buffer gets swapped out for a new frame and the monitor is set to draw the next perfect frame with no frame updates until that frame is done being drawn. This gives you a perfect frame every time. What this means, however, is that your fps can NEVER exceed the refresh rate of your display.
What are the downsides to keeping vsync enabled? There are a couple:
1) If your monitor doesn't support very high refresh rates at the resolutions you game at, you'll be limiting your highest frame rates to that of your refresh rate. But I say better to get a solid 75 fps of perfectly-drawn frames, than get 200 fps, drawn in pieces at 75 frames a second refresh (chopped up frames per above).
2) You could in theory be losing a tiny bit of performance since you are forcing the videocard to hold off on updates until the vertical blanking interval. In theory if you videocard is fast enough, or the action on the game screen is low, the videocard could have secondary and tertiary frames ready to go and be sitting with nothing to do, waiting for the monitor to finish drawing the current frame so it can begin work on the next frame. But in reality this is not a problem since you can't see (at least the full version) frames any faster than your monitor can display anyway.
So the next time some Quake 3 player brags to you about his 300 fps you can tell him that he's not actually getting that frame rate. And then watch as he tries to tell you yes he really is... 
As for where the settings are I use an ATI card now and it's got the vsync setting here:
The NVidia driver, I believe, defaults to vsync enabled for Direct3D applications and has a manual setting for it in OpenGL, but the latest drivers may have changed that.
Last edited by Merlin on Tue Nov 30, 2004 9:32 pm; edited 3 times in total |
|
| Back to top |
|
|
|
|
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
|
Powered by phpBB © 2001, 2005 phpBB Group
|
FAQ
Search
Memberlist
Usergroups
Register
Profile
Log in to check your private messages
Log in
