The Camera Zoom in Stereoscopic 3D

In Stereoscopic 3D Cinematography, doing a zoom will “compress” or Flatten depth. This is due to the nature of telephoto (zoom lenses). You normally “dolly in” on a subject of interest rather than zoom-in in 3D, so as to avoid that layered or flat 3D effect also called “cardboarding”.

So called, because even though the scene looks 3D, it’s as if every layer of depth has been hand cut and placed into the scene.

Overscan, Re-Framing, and of shooting 3D images in Epic Proportions:

With the emergence of Large sensor Cameras and high resolution image acquisition formats such as 4k, 5K (Red Epic) and now even 8K cameras such as the Sony F65, there is much talk in some circles about “re-framing” after-the-fact when doing principal photography in movies both for 2D and 3D.

Such kind of re-framing talk does not sit well with every Cinematographer, many of who for decades have grown accustomed to “baking-in” the framing of a scene at the time of capture. But just as the “look” of a scene is no more baked in at the time of capture, in this digital age, with the use of LOG capture (in simple terms the whole dynamic range of the camera sensor is captured raw) and later used to create an infinite number of “looks” for color, contrast etc…

…so also should there be an open mind to the possibility of Framing for, or in this case, useful techniques can be crafted by capturing “overscan” imagery and then zooming in on the region of interest in a scene.

Principal Photography  in Stereoscopic 3D calls for rewriting of the “rules”…

Infact in 3D cinematography, it is now an acceptable practice to frame a scene with a little extra “overscan” area. This assists the stereographer and editor in post production to sweeten or fine tune the depth budget of a scene and in some cases even save the scene from any overlooked stereo window violations.

Depth blending or Depth Ramping, the practice of bringing the outgoing scene and incoming scene to a comfortable viewing point for the audiences, between cuts in 3D, is also a time when shooting a bit of overscan saves the day.

The Clydozoom – A Non Cardboarding zoom in Stereo3D

(Watch the video in HD mode, pausing to read the annotations if needed. The video can be watched full screen on YouTube here.)

Performing a zoom in 3D… I call it the “Clydozoom”, is akin to the Ken Burns effect, but with the specific goal of executing a Zoom rather than a pan and scan or dolly-in or other such effect, and is aimed solely for Directors or Cinematographers who for any specific reason need a Zoom effect in their Stereoscopic 3D movie.

The Zoom  needs the following to be true in order to execute successfully:

1) The scene should be shot, captured or imaged on a sensor and pixel resolution much higher than the intended display or projection native format.

2) At some point during the zoom, H.I.T (horizontal image translation) might have be applied so as not to have any window violations.

3) The Image cannot be scaled larger than the native capture format, as this will lead to image degradation and/or magnification of parallax (causing possible background divergence and other issues).

4) The Clydozoom is a post processing technique, thus requires a stereoscopic 3D NLE or  compositing software such as After Effects, Nuke, or Adobe Premiere to name a few.

The benefits of this method of zooming in 3D is:

1) Saves time and Money on location, not having to re-configure/calibrate 3D Rigs or do extra 3D camera blocking for long shots to medium closeups in a scene (as in the case of the example video above).

2) NO cardboarding as witnessed in telephoto lens zooms

3) No magnifying of parallax as would occur if standard HD resolutions were scaled up to create a digital zoom.

3) No loss of image resolution or image degradation, as the source image is higher than the intended display or final projection format.

Clyd-o-Zooming in 3D at Live Action Events:

While the zoom technique described above is best executed in the confines of a post production suite, it would be interesting to see how todays real time hardware could in-fact be fine tuned to achieve this effect for Live Stereoscopic 3D productions such as 3D Sports, and Live events. This would require good “glass” (Lenses) and a large sensor camera with 4k or higher native capture capability.

Some thoughts…

1) If a realtime toolset is made available to Stereographers or online editors who sit in OB vans or at live production desks, they could steer a “virtual re-frame” box on the center of interest in a scene.

2) While the Live Camera is “locked-off” on this wide scene, the stereographer or live online producer steers the virtual viewfinder to the part of the scene that is of interest.

3) On pressing a “Take” button the system initiates a live Clydozoom by starting with the whole 4K or larger image resized down to fill the virtual viewfinder, and then do an automatic X- Y and scale translate move to accomplish the take.

4) Benefits of this method of doing Live 3D, is that the technique can be used as a mid-way transition between to actual Cameras on the location, a wide establishing camera, and one “close-up” camera that is framing the players/performers face for instance.

Using this technique, online stereographers wont have to worry about bad “depth jumpcuts”, Cardboard 3D as witnessed by telephoto lenses, or causing audience headaches from depth jumps between far and close action jump cuts.

(Note: These workflows are still experimental and being worked on at Real Vision. The techniques have not yet been thoroughly tested for every kind of scenario in 3D. Readers thoughts and further ideas are valued and welcome)

** Edit **

The ClydoZoom explained further…

I got a lot of Cinematographers and a few Stereographers as well asking questions, and as we are all learning (including myself) I thought it would be best to explain with pictures. I’m open to further insights…

The Setup: We will be using an After effects composition of  HD size and an HD image (1920 x 1080) to represent a 4K master image. In reality if we shot 4K originally, we would setup an Aftereffects composition of HD (or 2k) for our final out, and the original 4K master image in 3D would be scaled down to fit this final out composition.

…for our demo, as we do not have a 4K stereo image to play with, I use an HD 3d image to pose as the 4K master image, and I will setup an after effects composition of 640 x 360 pixels (3 times smaller than HD) to represent the final out HD screen size. All final out is meant for Cinema Screen Projection.

One of the biggest concerns I got via emails, was from Stereographers and Cinematographers about Parallax magnification if we “zoomed in”. Another concern was FOV changes, if we crop the sensor / image.

Click on images for larger.

Figure 1:  The Original HD image of 1920 x 1080 (meant to simulate the “4K” master image)

In Figure 1 we see the original HD image (simulating a 4k image). The onscreen ruler (excellent freeware) shows us a pixel disparity of approx 18 pixels. (for the Purists out there: ignore the fact that there is vertical mismatch of a few pixels in this image, and further ignore the fact that 18 pixels is too much for the scene, this is an uncorrected, and un- HIT image….) Let’s assume we are happy with this depth budget. Now… if we were happy with this 4K stereo image and 18 pixel disparity between left/right images, the first step we would do (regardless of zooming etc) would be to scale this down to final out of 1920 x 1080 if our final out delivery platform was HD.

This brings us to figure 2 below

figure 2: the final out comp of 640×360 (meant to simulate an HD or 2K final out)

Here we setup a  new composition setting of 640 x 360 pixels (simulating an HD final out). So we thus scale down our original “4k” image to fit into this final out for HD projection. The pixel disparity is now 8 pixels above, and is actually smaller than the original 18 pixels @ HD resolution.

So if this were an actual 4K image and the pixel disparity of the 4K image was 18 pixels, it would be reduced by almost the same factor when scaled down to HD rez.

Still with me?….

Figure 3: At 95% scale, we are back to a 17 pixel disparity (well within our original image’s disparity range)

Now… we perform the ClydoZoom, which is a combination of “windowing” or panning, or re-framing the oversized image along with uniform scaling of it, using all of the available resolution data of the original “4k” image at our disposal, so long as we DO NOT scale ABOVE 100% or the original image.

Thus at even 95% scale up (or…zooming in), we are still  back to a 17 pixel disparity… as we remember, right at the beginning we were “happy” with our 18 pixel parallax to begin with!

I hope this clarifies the ClydoZoom in more detail.

Lets address the other concerns:

Cropping the Sensor: We are not cropping the sensor at all. This is a post production technique, so all cropping is done on the master 4K image. Next in an Optical Zoom, arent we always changing the FOV? That’s what a zoom is really, a close up, and thus a change of the Field of view in the simplest sense.

Again… (Note: These workflows are still experimental and being worked on at Real Vision. The techniques have not yet been thoroughly tested for every kind of scenario in 3D. Readers thoughts and further ideas are valued and welcome)