Bricks in Motion
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Hi. Thanks to all those who helped me with my right mic. topic.
I need help. I want to make a greenscreen of moving clouds in the background of one of my films but I don't know how. Could someone help?
Thanks.
D.J.M.
Do you know how to do green screen and just need cloud footage, or do you want help with the green screen as well ?
I have had reeeaaaaalllllly bad experiences with green screening for my current project, which is why I have to refilm a heap of scenes and mask as an alternative because of spill (even though the subject was ove a meter and a half from the screen. If there are any alternatives to green screening, consider them.
If there are any alternatives to green screening, consider them.
Definitely. In a film I'm working on, I actually have some shots where I manually mask out the character to add a background so that I get a good key.
- Leo
I have had reeeaaaaalllllly bad experiences with green screening for my current project, which is why I have to refilm a heap of scenes and mask as an alternative because of spill (even though the subject was ove a meter and a half from the screen. If there are any alternatives to green screening, consider them.
Greenscreening is cerainly not as simple as it sounds! It starts with proper lighting of the subjects and the screen. It would be best if the screen was in a different country not just a meter away. But even with some spill, you can still get resonable results. But you do need a dedicated chromakey plugin for something like AfterEffects or Combustion. A good chroma keyer will allow you to subtract the spill from the subject matter.
Even with a good chromakey plugin, you still need to know how to use it. Often poor results are had when the operator tries to key the whole screen in one pass. It often must be removed in several if not a dozen passes. Each pass is also not just a simple key but includes several stages of masks and duplicate layers. You want to isolate just the few pixels that transitions between the screen and the image. These you key; the rest of the screen you mask out.
If you need a composite image, you should make every attempt to not have the two areas overlap. If they do, expect to spend hours at the job.
Riley wrote:I have had reeeaaaaalllllly bad experiences with green screening for my current project, which is why I have to refilm a heap of scenes and mask as an alternative because of spill (even though the subject was ove a meter and a half from the screen. If there are any alternatives to green screening, consider them.
Greenscreening is cerainly not as simple as it sounds! It starts with proper lighting of the subjects and the screen. It would be best if the screen was in a different country not just a meter away. But even with some spill, you can still get resonable results. But you do need a dedicated chromakey plugin for something like AfterEffects or Combustion. A good chroma keyer will allow you to subtract the spill from the subject matter.
I've been using After Effects CS3 with Keylight, and still I never get decent results. LEGO is too reflective.
Greenscreening is cerainly not as simple as it sounds! It starts with proper lighting of the subjects and the screen. It would be best if the screen was in a different country not just a meter away. But even with some spill, you can still get resonable results. But you do need a dedicated chromakey plugin for something like AfterEffects or Combustion. A good chroma keyer will allow you to subtract the spill from the subject matter.
Even with a good chromakey plugin, you still need to know how to use it. Often poor results are had when the operator tries to key the whole screen in one pass. It often must be removed in several if not a dozen passes. Each pass is also not just a simple key but includes several stages of masks and duplicate layers. You want to isolate just the few pixels that transitions between the screen and the image. These you key; the rest of the screen you mask out.
If you need a composite image, you should make every attempt to not have the two areas overlap. If they do, expect to spend hours at the job.
Wow, i dont think im ever going to try greenscreening, is bluescreening any different?
I think that blue-screening would come out slightly better, as blue doesn't contain any yellow (LEGO man colour), whereas green does.
ok, would like a blue peice of cloth work?
At one level it makes little difference what the color is. The real technical word is ChromaKey. Chroma being a fancy word for color. Weather/newscasters use various colors to key. For video work the color is normaly green. For photo work, blue is often used. But you could just as easily use orange, purple, or violet.
At another level, the key color is crutial. You want the key to be a fully saturated color that is as different from the actors and props as possible. If not, parts of objects start to disappear with a simple one pass key.
But the pros never use a one pass key. They key one area with one set of parameters, and another area with a different set. They may use 10 or more areas for "simple" shots and 50+ for more complex shots.
Riley, If you have Keylight, you have a great tool. You should be able to get a good key with multiple passes. Swing over to CreativeCow.com and monitor the AE threads. Several weeks of Google searching will also turn up lots of tricks the experts use. Puling a good key id not an afternoon's work! What you are trying to do is isolate via a mask one section of the scene and key that. That composite then becomes the source for a second mask that isolates a second area to apply a key with different parameters. As the action moves, you have to rotoscope the masks to stay with the action.
Riley wrote:If there are any alternatives to green screening, consider them.
Definitely. In a film I'm working on, I actually have some shots where I manually mask out the character to add a background so that I get a good key.
- Leo
How to you do this?
Do you know how to do green screen and just need cloud footage, or do you want help with the green screen as well ?
Both really.
DJM,
To mask or chromakey you need a special effects program like AfterEffects. In the case of masking you can also try the simple BSOD program written for brickfilmers.
In the case of chromakey, you provide the program two images. The foreground and the background. You then tell the solftware that whereever you see a paticular range of colors, you replace that pixel with the pixel from the background.
Masking on the other hand has the same two images plus a mask. You can think of a mask as a third image that is just black or white (or you can think of it as an Alpha Channel). If the pixel in the mask is black, you use the pixel in the foreground. If it is white you use the image from the background. With a mask you must hand paint a mask for each frame in the sequence. Some programs allow the mask to be various shades of grapy allowing you to feather in the foreground and background images. (Sometimes the black/white select deselt is backwards from the above. It all depends of the software and how you set things up).
That is Chromakeying and Masking in a nut shell. You still need the right software to do the job. Masking is the simplest and if you are really patient, you can do in a good photo editor like Photoshop or Gimp one frame at a time.
:)Thanks.
Just two things.
Your discription has given me an idea on what I have to do but I don't understand...
1. How to masking with gimp.
2. How I can mask a moving background.
I know I'm probably being a right pain in the *** but please help me.
Thanks.
D.J.M.
Maggosh, Opps! BSOL.
DJM.
Most graphic programs allow you to place multiple images over each other as layers. Put your foregorund image on top of the background. Select the foreground image and lower its transparency down so you can just see the background image. Select an appropriately sized erase brush. Carefully start to erase the foreground image to allow the backgrund image to poke out. (Control-Z is your best friend). When done collapse the layers and save your frame. Now you only have 99 more to go.
I do not know about Gimp, but Photoshop allows you to save a selection to an alpha-channel. After you do the first frame, you can start the second frame with the alpha channel restored from the previous frame. You now can restore and delete just the pixels that have changed.
This is a painful procedure if you have alot of action or a long scene to do.
High end programs like Combustion or AfterEffects will allow you to rotoscope the mask from frame to frame. This makes the job much simpler.
(And back to the chromakey concept, using a rotoscoped mask is what you need to do to isolate one small area to key.)
High end programs like Combustion or AfterEffects will allow you to rotoscope the mask from frame to frame. This makes the job much simpler.
Does this mean that your mask is a static image and then you tell AE the starting mask image position and ending mask image position (and any needed intermediate positions) and then AE will automatically move your mask according to your position parameters over the course of your video clip?
Correct. Rotoscope is a word that came about years ago when artists would hand draw masks on transparent material for each frame in an animation. This was done on a light table/projector device called a Rotoscope.
Nowdays, we rotoscope using keyframes in a computer. If you have a smooth motion, you simply need to draw a polygon shape for the first and the last frame and the program will calculate the "tweens" (frames between the key frames). If the motion is jerky, keyframes may need to be closer together or in the worst case every frame.
Both After Effects and Combustion (and any other special effects program worth its salt) will allow you to rotoscope a mask. Keyframing is not limited to masks. Most of these programs will allow you to vary just about any parameter from keyframe to keyframe. Things like the color of a drawn in circle, the color for a chromakey, even the framerate that the video will play back at.
Keyframes can also be calculated linearly or by a polinomial or a spline/Bezier curve. Curved interpolation gives much nicer results without jerky transitions. Human motion is much closer to a Bezier than linear motion.
Keyframe values can also be entered as equations of your own design. Making a composited ball bounce like in real life, a artist can use the h = 1/2Gt^2 + v0t + d0 equation and have time (t) be the frame index. I even have seen an entire book of math for the animator.
Keyframe/rotoscope is one of the major foundations of animation.
Last edited by FLL-Freak (January 16, 2009 (05:01am))
Maggosh, Opps! BSOL.
DJM.
Most graphic programs allow you to place multiple images over each other as layers. Put your foregorund image on top of the background. Select the foreground image and lower its transparency down so you can just see the background image. Select an appropriately sized erase brush. Carefully start to erase the foreground image to allow the backgrund image to poke out. (Control-Z is your best friend). When done collapse the layers and save your frame. Now you only have 99 more to go.
I do not know about Gimp, but Photoshop allows you to save a selection to an alpha-channel. After you do the first frame, you can start the second frame with the alpha channel restored from the previous frame. You now can restore and delete just the pixels that have changed.
This is a painful procedure if you have alot of action or a long scene to do.
High end programs like Combustion or AfterEffects will allow you to rotoscope the mask from frame to frame. This makes the job much simpler.
(And back to the chromakey concept, using a rotoscoped mask is what you need to do to isolate one small area to key.)
Thanks, I thinkI might know what to do now.
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