Question about fields rendering.

Hi !

I have done an animation (still on my museum project) and the film is nice on a computer, but I want to burn a good quality DVD to be played on a stand alone DVD player. So I render a new film using the field option.

I was expecting this sequence :

Even field for frame 1 - Odd field for frame 2 - Even field for frame 3 - Odd field for frame 4 - …

Bad surprise: the computing time is multiplied by 2. Blender seems to calculate full images for each frame instead of calculating only the needed fields and interlacing them !

Am I wrong ?

Is there a way to use the field option without increasing by 2 the rendering time ?

Thanks in advance.


this is what i found in the documentation (including answer to your speed-question):

Thanks Solmax, but I have got the Blender guide, and this doesn’t answer to my question. :frowning:

As the frequency of fields is 50 Hz, and the number of full image is 25 per second, the odd field is shifted in time with a 1/50 s delay. So, there is no need to calculate the full frame every 1/50 s, but only a field.

The rendering with fields option toggled should take the same time as the rendering without fields, but Blender seems to calculate a full image every 1/50 s and after displaying this image, then keep only the needed field and make a picture adding an even field and an odd field.

Half of the computing time is lost !

For a 1 min 50 animation with raytracing, that should take 10 days, it takes 20 days !

[>] My question is: is there a way to avoid computing unusefull fields ?


not sure about this, but it may work better in post-production. do you have combustion or afterFX? i’m quite sure they can output interlaced video from non-interlaced footage. even virtualDub might do it.

i tried rendering with fields in blender, and now i know what you mean. blender does calculate only half of the height, but for some reason all together takes longer then non-interlaced. i compared the rendering times, and it seems that rendering with fields takes around 1/3 more time than w/o fields.

My guess is that because it has to advance 0.5 frames between even and odd frames, it has to do twice the animation calculation (like animating Fiber grass, calculating armature deformation, etc) but the same amount of render calculation?

IIRC DVD content can be encoded “progressive”. In that case the DVD-Player does the interlacing for TV output. That way you wouldn’t have to care about fields.

I noticed this in a recent commit:
ton fixes field rendering bug
dunno if its related, just thought you might be interested.

Thank for all your replies.

Progressive incoding doesn’t give the same quality, because the inter frames are not existing, and the animation is not smoother.

On the screen, Blender seems really to calculate complete frames, even if it displays Field A or Field B in the menu bar.

I can see it building a complete picture with no “comb effect” or black lines for the field A and for Field B. After that, it displays for some seconds the interlaced frame (comb effect) made with Field A+Field B.

Half of the lines calculated seems to be lost !

If only Fields were calculated, I think I should see a picture with black lines during Field A calculation and an other with the same appearance, shifted down by one line during Field B calculation.

Am I wrong ?


When I try with Blender 2.34, the rendered fields are only half the height of the full image. So there are no wasted lines here. The rendering time with fields is longer because the geometry setup has to be done twice (frame 1 and frame 1.5 instead of frame 1 only).

ROUBAL, I think you seem to be missing how fields are used.

Pal is 25 frames per second, 50 fields per second. There are two fields for each frame, that contain half the number of horizontal lines of a frame each.

Now to get extra smooth motion, each field is sampled at a different point in time, so while the full frame is only updated at 25 Hz, new imagery appears on screen at 50 Hz. It’s not the same as 50 progressive frames per second, or the same as 25 progressive frames per second.

That is why still images from video display the comb effect, because the single frame is made up of two samples in time.

So when Blender renders a frame with fields on, it renders half the horizontal lines, then advances forward in time by 0.5 frames, renders the other half of the horizontal lines, and that’s the frame. When this is displayed on a TV screen, half the fields are displayed, then 0.5 frames later the other half of the fields are displayed.

Hi Broken.

I am electronician, and I perfectly know how fields works, but on my computer, fields don’t appear with half height size like usagi says!

I have asked the question to a french friend who is also a Blender user (I’m french) and he told me the same thing that Usagi says : the calculated fields are displayed half size vertically. In this way, it is easy to see that only one field is calculated at a time.

He is far from me, so I haven’t seen it myself on his monitor, but I can tell you one thing: on my computer, this do not happen ! I see a full size image for each field A and B !

The rendered AVI raw file is perfectly encoded with 1/50s shift between fields, and the animation is very smooth and clean on a TV set, but the rendering is very long!

[!] At the moment, I wonder if it couldn’t be a bug with BlenderIntel, because I always use it for huge renderings, and I have never used the field option before, and maybe it works normally with the official Blender 2.34!


Well… I have checked all the versions of Blender that I use : 2.33a and 2.34 official and BlenderIntel…

Same result with all of them !

The answer is not here !


You’re shooting to an interlaced monitor? Isn’t HDTV non-interlaced?

I also use blenderintel without problems. Can you post a simple .blend that we can test on our computers?

No matter the Blend file… I have checked various files, with the same result…


Just for your info, this is the standards for the U.S. (digital):

720 lines (progressive); 1280 Horiz pixels; 16:9 aspect; 24, 30 or 60 Hz
1080 lines (interlaced); 1920 Horiz pixels; 16:9 aspect; 60 Hz
1080 lines (progressive); 1920 Horiz pixels; 16:9 aspect; 24 or 30 Hz

U.S. Analog:

Total Lines: 1050
Active Lines: 960
Vertical: 675
Horiz: 600
Aspect: 16:9
Freq: 8 MHz

Europe Analog:

Total Lines: 1250
Active Lines: 1000
Vertical: 700
Horiz: 700
Aspect: 16:9
Freq: 9 MHz

Just for your info :smiley:

What I meant was: Post an arbitrary file that doesn’t work on your machine and I try it here, check the settings and such … Maybe I get some insights, because at the moment I have no clue what could be the problem.

Simple answer to your question.
I am guessing that you are rendering with the Dispvie button on.
Try rendering with Dispwin on instead.

What you are seeing is a stretched version of the odd field, then a stretched version of the even field, then the combined image just before it is saved. It is not really rendering a full frame for each field, it just appears that way when the render is displayed withing the 3D view.

Here is another way to visually illustrate the point.
Set render size to 25% and render one frame with fields turned on then with fields turnd off. You should be able to see duing the render that one field has only half as many lines as the full frame.

As far as render time goes it takes longer because the geometry must be calculated twice for very frame even though the same number of lines are being rendered as without fields

Now I know how you are called Superdan ! You are Super !

Yes, that is the explanation. I used only the Disp view option, and it shows a stretched picture. The picture displayed in the Disp Window mode shows the half height picture !

Thanks for cleaning my brain !