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Is this possible with Green screen?

Jackson Wong's picture
Last seen: 9 hours 25 min ago
Joined: 01/07/2011 - 5:16pm
Administrator Plus Member

I am currently putting together a video segment of an afternoon's walk of several kilometres (or 'miles', if that's what you 'do' in your neck-of-the-woods). Each portion of the overall sequence of about twelve minutes duration, is introduced by a widish-angle 'panoramic' shot taken from a tripod, which shows the track to be traversed, clearly. The intention, (and it's well on the way to fulfilment, since everything 'works'), is to animate an ever-extending white-line from end to end of the walked-over landscape-shot in full-screen, indicating progress and at any one time, and, optionally, to run the corresponding video shots in a reduced-size window. The technology is perfected, and the line travels, ever-extending as the corresponding, directly-obtained shots keep pace in the smaller 'window'. Being able to run the smaller window allows me to intermix 1920 x 1080 and 720 x 576 shots without the latter appearing to be at a disadvantage. The whole effect is created by laying-out on a photograph, the same size as the finished images, the line to be traversed in 'chroma'-compatible green, which has been lightened slightly in tone, so as to be 'visible' against the true 'chroma' green of the typical green-screen process. Both greens have been selected so as to 'disappear' when the 'chroma' function is invoked. That is then selected, and 'lifted' by means of 'copy', and plonked onto a blank 'green-screen' of 1920 x 1080 pixels. It's merely then, a matter of tracing the final 'white-line', frame by frame onto the green blank, using the 'pilot' slightly-lighter line as a guide and extending the line in even steps. It works brilliantly, but for one thing. My beautiful crisp tidy 'lines' once saved as 'frames' (one to each 'step') and brought back to the screen again, at rendering-time, have pixellated badly at the edges and no-longer stand-out against the background as they were first drawn. On projection, the lovely crisp and accurate line has gone muddy, due to the numbers of pixel which are now, neither green, nor white, but somewhere in-between, and with a line only four pixels wide, that means, effectively, the entire line.

My question, then, is this: Is it possible to save this material as a series of 'unmerged' images so that the outlines remain crisp, clear and well-defined? Has anyone 'out-there' had to overcome this problem and is able to point me in the right direction? All suggestions welcome.

Ian Smith

Dunedin - New Zealand


artsmith's picture
Last seen: 6 days 3 hours ago
Joined: 03/02/2011 - 9:06pm

Just a footnote. I have doubled the green-screen image size to 3840 x 2160 and reduced the image-size again, from there, when it has become necessary, It had made some improvement (and I have used that method, often, when creating'chroma-based' screen-objects which were static, andonly called for a single frame of information), but the files-sizes are, of course, horrendous.


artsmith's picture
Last seen: 6 days 3 hours ago
Joined: 03/02/2011 - 9:06pm

I forgot, when posting last, to mention my 'fall-back' graphic, if I am unable to secure the results I want with the methods I have already described. I frequently carry a Garmin 'Oregon 450' GPS with me, especially following an unfortunate event where I failed to return home by nightfall after day spent in thick 'bush', accidentally following an illegally-marked trail, and had my old GPS quit on me due toimpenetrable bush-cover overhead. My night-out in the open bush, waiting for sunshine the following day, (which enabled me to navigate my way out using my wrist-watch and the sun's position), had out, searching for me, 50 Search-and-Rescue personnel, the police, a helicopter and two boats out-at-sea; something of which, to this day, I do not care to be reminded, particularly. The problem had been that of getting a message 'out', as, in the area, cellphone coverage was zilch, and I don't carry one anyway. It's no big dea; I have had nights out in the bush before, but, of course, that was before I was married and had a family at home to report that I was overdue. I was in no danger, (we have no snakes, nor bears, only possums, deer and pigs), and the only respectwhich gaveany cause for concern, was that during the day, which had been stinking-hot,I had gulped down two-thirds of my single bottle of water.

However, I have created a handy little 'mask' consisting of a graphic of my GPS, physical,which I have also reproduced, rotated 90 deg to the left, and also to the right for those instances where I am moving, effectively across the screen, rather than up-and-down, (when I use the normal, unrotated view).

Now, the screen of the GPS, in the graphic, has beenreplaced by an area of 'green-screen'. I also have the map in my computer appropriate to thearea I am travelling-in. The nature of the actual GPS display makes it useless for reproduction as a means of showing routes travelled on video, but small areas, copied off the map are ideal and quite visible, even though the GPS and its window only occupies a corner on the lower left-hand side of the screen. It is easy, to animate a travelling line over part of the map in the GPS's 'window' to give an indication of where I am at any one time, (themarked-route must, of course be absent from the portion of the map, in-use, as you have to animate, frame-by-frame, a 'new' line onto it). Magnified, somewhat, the screen image on a GPS seems to be somewhat pixellated, at any time, and then, it is quite in-order to use a line which pixellates naturally, as that falls into-line with the rest of the image. Simple, and works extremely well.Only disadvantage is, that it is a bit small.