All Things Color for Film and Digital Cinema
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Posts Tagged ‘3D cinematography’

3D Theatrical Projection Problems with Floating Windows – Keystoning

As noted in a prior post on “Floating Windows” there is somewhat of a problem with the theatrical screening of 3D whereby cinema screens cannot for various reasons project a full screen DCI compliant image without physical image masking. Below I outline some possible solutions to this problem.

The main problem with both the theatrical presentation of 2D and 3D Feature Films is the tendancy for a cinema to be designed where the projection device is situated at the rear upper level of the auditorium. This old model of cinema design requires that the image be projected downwards over the distance of the auditorium to the screen. The physics of this basic model there for assume that the image will be somewhat keystoned by the time it reached the screen. To then counter the effect of a trapeziod shaped projection image on the screen one would then employ cinema black masking and essentially over shoot the image into the blacks until a nice pleasing rectangle is created.

For this very reason a ‘projection safe’ or ‘action safe’ model is employed by 2D image creators whereby, just like television, images were made to be displayed with a 5% ‘masking’ tolerance. Some screens may see the full image and most would see somewhere between that and roughly 5% – 10% in.

You can see now that if in a 3D presentation you are employing the use of ‘floating windows’ to counter 3D edge violations or simply play with the 3D screen dynamics these will more than likely be lost. Unfortunately as these windowing techniques are employed to assist with the audiences comfort factor when viewing 3D materials their exclusion from the presentation will make the experience slightly more uncomfortable.

Lets look at the below screen setup.

  • Screen Width – 30 Ft Screen
  • Screen Resolution – 2048
  • Auditorium Depth / Projector Throw- 100 Ft
  • Tilt of Projector – 10 Degrees

Given the above scenario, without masking, our image is now 30 foot across on the top of the image and 29 foot along the bottom. 28/30 = 93%

Top Width = 68″9′

Bottom Width = 76″1′

Keystone % = 100 * (top width-botom width)/top width = %9

9% of 2048 = 184 pixels.

Generally FLoating Windows will not be more than the max Positive Disparity which ona 30ft screen would not be more than 28 pixels Either side.

Well…with the calculations above we just lost our floating windows.

Bugger!


iRiS Stereoscopic Base and Disparity Calculator – 1.1.0 Update – Introducing the Roundness Factor

The Stereoscopic Base and Disparity Calculator 1.1.0 for the Android OS has just been updated and introduces a new base calculation measured around the perceived on-screen Roundness or depth of an image.

The new option allows the user to either :

  • Calculate the camera base separation using a predetermined target parallax amount
  • Calculate the camera base separation to a “Roundness Factor” of 1.0.

The Roundness Factor represents the factorial difference in depth between the photographed scene and the resultant projected 3D scene.

It is generally referred as a factor because ideally one would want to capture and project the same depth representation of photographed object, thus having a factor of 1.0.    IE: Physical scene depth/perceived 3D on-screen depth.

If the Roundness Factor is less than 1.0 then for example a round sphere will appear flat and compressed. It will have lost is dimensionality.

If the Roundness Factor is greater than 1.0 then the same sphere will appear stretched or extruded on the Z depth plane.

Consider dimensionality in filming the close-up of someones strong angular face. Captured with perfect roundness the 3D on-screen projected face will feel volumetric and proportionately correct. If the “Roundness Factor” starts getting too high the persons head and nose will begin to feel stretched toward the viewer, which is not such a flattering look.  In this sense it is better to err on the side of a factor less than 1.0.

The effect of Roundness is related very closely to Lens selection. A longer focal length lens will have a much greater impact on roundness and Parallax as the base separation in altered. On a 75mm Lens it takes only small changes in Base distance to make quite large differences in background parallax and therefor depth.   Additionally sensor size is quite an important factor to consider as the resulting 35mm Lens equivalents could be a lot higher than you think.

As always it is recommended to test Lens/Sensor configs as much as possible before entering any project.


Adrian


iRiS S3D Stereo Base and Disparity Calculator Released

The S3D Base and Disparity Calculator is now officially released on the Android Market.

The S3D Calculator is divided into three Main Screens.

Navigating between the screens is performed by swiping the current page with a horizontal finger gesture.

  1. Initial Simple Base Calculation
  2. Base and Disparity Evaluation and adjustment
  3. Disparity Overview and Analysis

Simple Base Calc

Input Options Include:

  • Camera
  • Camera Active Area
  • Lens
  • Screen Size
  • Screen Resolution
  • Parallax Target
  • Distance Measurement Metric (Meters or Feet)

Base and Disparity Evaluation and adjustment

Disparity overview and analysis

Output Data Includes:

    • Base (inter occular Distance)
    • Field of View
    • Angle of View
    • Total Pixel Parallax
    • Total screen Parallax %
    • Total Screen Parallax (mm)
      • Positive Parallax
      • Negative Parallax
    • Zoom Required
    • Post Convergence Required

    Regards,

    Adrian


    s3d stereoscopic Base and parallax / divergence calculator for Android

    ScreenShots from forth coming s3D Base and Parallax Calculator for Android.


    3D – How to “FreeView” 3D Stereoscopic Images

    FreeView 6

    The above is an example Stereo Pair 3D image from the 3D Feature Film “Cane Toads” . (Double Click on the images for larger versions.)

    3D FreeViewing , unlike other 3D viewing methods, does not require any other apparatus or special equipment to view an image in 3D. As a viewing method is more associated with viewing stills and 3D previs as it can be quite a strain on the eyes to view motion picture images this way for a prolonged period. The 3D FreeView method does however render a beautiful 3D scene as there is no Crosstalk between the Stereo pair that is otherwise apparent in most other electronic 3D viewing apparatus.

    Analog systems like the “3D Viewmaster” are also produce very pure viewing methods.

    3D ViewMaster

    This ‘FreeView 3D’ image is composed of stills from both the Left and Right Eye. The Right Image is from

    the Left eye and the Left Image is from the Right eye. When viewing you have to go somewhat crosseyed for your brain to fuse the two images together as a 3D image. See Below.

    How to FreeView 3D

    1. Look at the pair of images on the screen. (Double click the image for a larger version)

    2. While still Focusing on the Screen, Hold one finger in between your eyes and the image onScreen. You will see your finger as two ghost images.

    3. Still focusing on the screen, move your finger towards, or away from, the screen until the tip of your ‘ghost fingers’ align with the two circles.

    4. Now focus on your finger. You will now perceive 3 ghost circles behind your finger. The centre circle will be the fused 3D image. (You may have to rotate your head a little so that the 2 images align vertically.)

    5. Here is the tricky bit. While still focusing at the point where your finger is, move your finger away to reveal the 3D image behind it. For beginners your eye will naturally want to focus back to the screen so for a while you can help your brain fuse the 3D by leaving your finger slightly in view.

    The result will be that in this case you see the green dot sitting forward of the black circle in 3D space.

    With practice you will find it second nature. I had looked at many 1990′s stereograms or “magic eye” pictures in my youth so I picked it up quite quickly :)

    Free-View 2

    Have fun.

    Adrian Hauser


    “Cane Toads – The Conquest” 3D – Mark Lewis – 2010

    Cane Toads – The Conquest

    (2010)

    Director - Mark Lewis

    DOP’s - Paul Nichola, Toby Oliver, Kathryn Milliss

    Grading Platform - Baselight 4

    Format - SI2K 3D


    Below are stereo Pair FreeView 3D images. Click on this link for more information about viewing how to view FreeView S3D images

    FreeView 1

    FreeView 2


    FreeView 3

    FreeView 4

    FreeView 5

    FreeView 6

    FreeView 7

    FreeView 8

    FreeView 8

    FreeView 9


    Floating Windows in 3D post

    The use of Floating Windows can help aid 3D problematic sequences and shots where images with a negative parallax (forward of the screen) break the edges of the screen plane. These are called Window Violations.

    <IMAGE_1>

    By manipulating the image boarders with masks one can help reduce the breaking of the immersive illusion. These masks can serve two purposes.

    Firstly they can help reduce the curse of retinal rivalry where an object on the edge of screen is present in one eye and not the other.

    <IMAGE_2>

    Secondly they can perceptually bring the screen plane forward or backward to become inline with an object of negative parralax that is breaking the screen edge.

    <IMAGE_3>

    Depending on the camera or object motion through the shot the Floating Windows can be dynamically tracked to match.

    <IMAGE _4>

    Unfortunately there is a bit of a problem with this function in the real world theatre though. I watched a 3D kids animation feature on the weekend and noted the projected image was (as usual) projecting into the theatre blacks surrounding the screen. (In 2D cinema we can usually use a TV like 10 percent safe area to imagine worst case scenario projection masking.) Because of this the floating windows of many shots became nulified as they shot into the blacks and therefor many shots broke the screen window somewhat uncomfortably that would have been otherwise fixed with this technique.

    Additionally Floating Window effects are also masked due to keystoning of the projector itself. Most theatrical cinemas have their projector raised almost to the level of the top of the screen which naturally causes keystoning. The easy way out of this is to increase the theatre masking so that a true rectangle is projected. This will most definitely mask the Floating windows as well. Some distributors would prefer the image was left full frame in a trapezoid shape that included all floating windows.

    Adrian