Preview Resolution
by Richard Benfield
on
Sep 14, 2009 at 10:38:34 pm
I have tried to find information on this. However, I have not been able to find any. I am hopeful that among the experienced users here, this may be a quick and easy answer for someone.
I have a user who is concerned that the preview panel in Adobe Premiere Pro CS4 does not accurately represent the material. I believe that this is a normal (and imho acceptable) behavior. It seems to me that the preview panel is intended to provide only preview quality and not final render quality. None the less, I had to research this and ensure I am providing the user and management with facts, not my opinion. And I would like to make sure that if there is a way to remedy this, I am able to provide that to the affected user.
I have confirmed that if I open a pre-rendered video that is to be used in a sequence, it looks as it should. I then import that same video into Premiere Pro and making no changes what so ever, attempt to preview it, there are some distortions and artifacts (albeit very subtle). These are primarily aliasing along high contrast diagonals. Once run through Adobe Media Encoder the resultant video looks as it should.
As I looked into the images and compared the original with that from the preview panel, I noticed what I believe is the cause. Despite having "Quality" set to "Highest Quality" and "Magnification" set to "100%", it appears to actually be the wrong resolution and therefore aspect ratio. The source and resultant videos are 720x480. However, the preview panel is actually displaying at 655x480. So instead of the native 1.5:1 ratio, it is being displayed in a 1.36:1 ratio.
So my questions are:
Does that information sound accurate?
Is there any way to make the preview panel display at the correct resolution and aspect ratio?
Are there any other ways within the Adobe suite to more accurately preview the output without fully rendering it?
Thanks in advance for any guidance you may be able to provide.
Re: Preview Resolution by mike velte on Sep 15, 2009 at 10:26:50 am
I have seen video cards that do not support the aspect ratio of the monitor and everything looks stretched. I have added a title with a perfectly round circle over a DV sequence. Set the zoom level to 100%, hit the tilde key to fill the monitor and measured the circle with a ruler...it is round.
Try it...is yours round?`
Re: Preview Resolution by Richard Benfield on Sep 15, 2009 at 4:28:57 pm
Hi Mike,
Thanks for the response. My displays are fine. I have two Dell 1908FPs with a native resolution of 1280x1024. They are both driven by a NVIDIA Quadro FX 1700 and are running in their native resolution. Also the problem is noticable on the same display when looking at the source vs. the preview vs. the render.
Thanks for that suggestion, it was actually a very interesting test with some unexpected results. Before I write my little book explaining what I did, I would ask (if you have an opportunity) for you to export your title to a Bitmap and measure it again. I wanted to upload my results, but they are too large and I can't access my website right now. I will try to access it later and upload the images and link them from this thread. As an aside, the way I was using it, I had my Preview Panel undocked and on my second display, set to 100% and sized larger than the preview. However, for the sake of consistency with your suggestion, I did not use it that way for the tests below. Instead I did everything on the primary monitor as you described. That said, here is what I did and what I found.
I created a new project using the DV - NTSC, Standard 48kHz preset.
I created a new Default Still, Title.
Within the Safe Margin, I created a perfectly round white circle (shift drag) and centered it.
Within the white circle, I created a perfectly square black rectangle (shift drag) and centered it.
I added the title to the sequence and expanded it to 15 seconds.
I selected the preview panel and pressed the tilde key.
I measured it and then I took a screenshot and cropped it to only the black back ground portion (the actual preview).
I pressed tilde again to revert to the normal view and selected File, Export, Media.
I selected Windows Bitmap for the Format and NTSC Bitmap for the preset and saved it.
Results at the bottom
Then using an image editor, I created new blank image with a 720x480 canvas.
I created a perfectly round black circle against a white background.
I created a perfectly square white rectangle in the black circle.
I saved it as a 24 bit Windows bitmap for use in a sequence.
I created a new project using the DV - NTSC, Standard 48kHz preset.
I selected File, Import and opened the test pattern bitmap.
I added the imported bitmap to the sequence and expanded it to 15 seconds.
I selected the preview panel and pressed the tilde key.
I measured it and then I took a screenshot and cropped it to only the black back ground portion (the actual preview).
I pressed tilde again to revert to the normal view and selected File, Export, Media.
I selected Windows Bitmap for the Format and NTSC Bitmap for the preset and saved it.
Results at the bottom
Measurements were confirmed by checking the canvas size and number of pixels high and wide in the resultant bitmaps.
Adobe Title Results
Previewed Measurements
Circle - Width and Height were Equal 378x378 pixels
Square - Width and Height were Equal 275x275 pixels
Canvas - Width and Height were 655x480 pixels
(Note: The circle and square were the correct aspect ratio, but the canvas was NOT)
Rendered Measurements
Circle - Width and Height were NOT Equal 415x378 pixels
Square - Width and Height were NOT Equal 303x275 pixels
Canvas - Width and Height were Correct 720x480 pixels
(Note: The circle and square were NOT the correct aspect ratio, but the canvas WAS)
Imported Test Pattern Results
Source Measurements
Circle - Width and Height were Equal 477x477 pixels
Square - Width and Height were Equal 330x330 pixels
Canvas - Width and Height were 720x480 pixels
(Note: The circle, square, and canvas were ALL the correct aspect ratio)
Previewed Measurements
Circle - Width and Height were NOT Equal 434x477 pixels
Square - Width and Height were NOT Equal 301x330 pixels
Canvas - Width and Height were 655x480 pixels
(Note: The circle, square, and canvas were ALL the WRONG aspect ratio)
Rendered Measurements
Circle - Width and Height were Equal 477x477 pixels
Square - Width and Height were Equal 330x330 pixels
Canvas - Width and Height were 720x480 pixels
(Note: The circle, square, and canvas were ALL the correct aspect ratio)
Can anyone else confirm this behavior? If this is correct, then it means that not only are things not rendered in the preview accurately (not that big of a problem), it also means that Titles and possibly other content added by Premiere Pro, is not rendered correctly in the exported media (more of a problem).
Re: Preview Resolution by mike velte on Sep 16, 2009 at 10:43:43 am
Interacting between Premiere in a non square pixel sequence and an image editing app will cause round to be elipse. The excpetion is in a Photoshop NTSC preset. one can create a round circle, It will appear round in Premiere, export round to an NTSC monitor, but playback elipse on a PC monitor.
Exporting a Bitmap from Premiere, open a new NTSC preset in Photoshop and Place the bitmap into it...elipse!
Previewing NTSC should be done on an NTSC monitor or Premiere's program window..
Re: Preview Resolution by Richard Benfield on Sep 17, 2009 at 5:31:48 am
mike,
Thanks for the reply. Though I haven't had a chance to try creating an NTSC bitmap in PhotoShop yet, I did find the answer and another solution. I will explain what I have learned below. Don't feel compelled to read it. I dont presume to think I will be explaining anything new to you or Vince. I am really just posting it for anyone who may search and find this thread. But if you do get bored and what to read it... enjoy... :)
Thanks,
Richard
Ok, hopefully someone finds this helpful one day...
The answer was in reading about Pixel Aspect Ratios. I had to read and read and read... and then read a little more. The problem seems to be the complete lack of consistency as to the terminology and the math behind it. Where AR = Aspect Ratio, I have found information on... Sample AR, Image AR, Picture AR, Pixel AR, Frame AR, Display AR, some of them are used incorrectly in different places. Most of them are explained inadequetly (at least everywhere I looked). And the math never worked. Ok, well sometimes it worked, but when it did, it said that the PP preview was incorrect. At 655x480, it just always came out wrong when I tried to calculate it. So let me sum up what I believe I learned and maybe help someone else out that may search and find this thread later. Some of this I had known for a long time, some of it was a new found application of the old knowledge. Anyway, here is my summary of it.
Aspect Ratio is the quotient of somethings width and height.
SAR or Sample AR, Image AR, Picture AR, & Frame AR all appear to be the same, that being the aspect ratio of the picture or videos resolution. So a video with a resolution of 720 x 480 will have an SAR of 1.5.
DAR or Display AR is the aspect ratio that an image is displayed at. If the image is displayed full screen then it is also the aspect ratio of the display device. If the display device uses square pixels then it is also the aspect ratio of the images displayed resolution. So an image displayed at a resolution of 640 x 480 will have an DAR of 1.333 (repeating).
PAR or Pixel AR is much more difficult. I have seen it defined as the aspect ratio of the actual pixel. I have also seen it defined as the quotient of the SAR and the DAR. While I kept on inferring that these were only related to the playback pixels, they are also applicable to the capture pixels. So the capture device or resultant image also has a PAR. And if the capture/image PAR and the playback/display PAR dont match, the image will not look right.
Among the things it explains is that DV NTSC is .91 (which is closer to accurate, but still not quite right) and that PP will show the PAR it believes an file is based on. When I create a sequence it asks what preset to use. When I look at the DV NTSC preset, it shows the PAR is actually .9091. When I import a Type 2 DV video, it shows that its PAR is .9091. When I import a bitmap, it shows that its PAR is .9091... (Did you catch that?) As indicated by mike, bitmaps created in normal image editors are square (well the pixels are). The PAR is actually 1 not .9091. Thankfully, that same web page explains that you can manually correct the PAR by using the Interpret Footage dialog box. Immediately upon chaging the bitmaps PAR it was re-rendered in the program monitor correctly.
Well that is all fine and well, but what about this 655 x 480 business in the program monitor? It just didnt make sense... until I calculated the PAR for a 720 x 480 SAR and a 655 x 480 DAR. The result? A PAR of .909722... Finally, it makes sense. A little more math showed me that 655 x 480 using square pixels is as close as you can possibly get to a PAR of .9091... So there it is... mystery solved. So in fact, it would appear that PP program monitor is the only player on my computer that will accurately display a 720 x 480 video with a PAR of .9091 such as Type 2 DV... the other players I kept using as a reference were displaying it with an incorrect PAR of 1. The only thing that PP did wrong. was assume that my bitmap had a PAR of .9091 instead of 1. But since it has an easy method to manually change the clips PAR. its point Adobe...
Re: Preview Resolution by Richard Benfield on Sep 17, 2009 at 5:18:21 am
Hi Vince,
Thanks for the response. The problem was in fact related to the pixel aspect ratio. I will post my little 'book' explaining my findings, in a response to mike at the end of the thread. Just in case your bored and want to read it... :)
Re: Preview Resolution by Richard Benfield on Sep 17, 2009 at 5:14:02 am
arc,
Thanks for the reply but I was using High Quality. However, it still showed 655 x 480 playback resolution. I will explain why at the end of this thread.
