Wednesday, March 19, 2014

Fish-bowl on a tree stump scene - photo-real integration of 3D model

- Assessment 2 -

Fish-bowl on a tree stump scene

Photo-realistic integration of pre-existing 3D model into an original still frame photographic background plate



On set measurements and Camera data for the background picture

The goal was to place a pre-existing 3D model of a fish-tank into an original photographic background and make it would look photo-realistic. The fish-bowl contains my custom 3D models of the shield and the armour with glowing effects on it.
The scene in the composition is situated in a forest meadow with a tree stump with a fish carved into it.

The light conditions of the background picture are determined by the time and location of shooting.
The picture was taken in the location of Cardiff Bute Park on Sunday the 16th of February 2014 at 16:36, it was an early spring sunny day - the Sun was low at that time, creating long shadows and visible light beams.
The light source in the scene - Sun - is placed on the right side of the picture – object on the right are lit and casting shadows to the left side of the image.

Original image and camera data:

Camera model used:   PENTAX *ist D
Dimensions:                3008 x 2008 pixels
Resolution:                 72 dpi
Color representation:  sRGB

F-stop                           f/8
Exposure time              1/125 sec
ISO                               ISO-200
Focal length                  24 mm
No flash.

Distance of the camera from the ground:    approx. 5’8 feet
Camera positioning in Maya was done by eye, as accurate as possible.
No lens distortion grid used, it was not necessary for the sake of making the shot looking good.

Image scale

I rescaled and cropped the original image using Photoshop from the original size 3008x2008 to 1920x1080 which is the resolution I wanted to render out from Maya.

Autodesk MAYA

Camera settings adjustements

First of all I found my camera attributes at DPreview website. I needed to find specifications for my camera sensor, because my camera sensor was smaller (cropped) than the Maya Default camera sensor.
Therefore I made adjustments to Maya camera attributes according to following calculations:

Camera used:                   Pentax *ist D
Sensor size:                       APS-c  (23.5 x 15.7 mm)
Inches:                                0.9252 x 0.6181 inches
Original Focal Length:    24mm

Default Maya sensor size:            36 x 24 mm
Inches:                                          1.417 x 0.944
Default Maya lens:                       50 mm

36 / 23.5 = 1.5320
24 / 15.7 = 1.5287

1.5320 + = 1.5287 = 3.0607 / 2 = 1.5304 (average)

1.5304 * 24 (original focal length) = 36.7272

-> New Maya lens size based on cropped sensor = 36.7272
-> Wrote that number to Camera Attributes – Focal Length

In Maya I created a camera and add the rescaled background image to it as Image Plane.
Placement – Horizontal, Fit to Film Gate.

Setting the object in the scene

I created a Polygon Plane on the ground and moved the camera around to set it to a correct place in the scene. I applied Use Background shader to it. I set the Reflectivity little lower, Specular color White. The purpose of this plane was to create shadows in the scene but stay hidden when rendered.

I went through quite a lot of struggle of figuring out how it works, about setting on and off the Primary visibility, so the plane will not be seen in the render but it would still provide the shadows.
I also had to shape the plane manually in order to cast the shadow only on the top of the stump and not to exceed it.

In the beginning it looked like this when rendered:

Rendering the whole scene from Maya

At the beginning I tried to render the whole scene straight in Maya, no Nuke compositing. 

Render test1
Render test2  
Render test3
Render test4 - with Ray Tracing switched off
Render test5 – Ray tracing low
Notice how the objects in the back of bowl are distorted and big

Render test6 – Ray tracing final look

Even though the last results were nice, later on I decided to not go down that road and do it the more complicated way instead – rendering individual layers and then composing them together.



In order to make the procedure work the same way I created the ‘Forest Armory’ scene (i.e. to create several separate render passes and compose them together individually), I would have to hide the Reflections of all the objects in the Render Stats attributes in the scene

That could not be done because the objects were too complicated and made of many separate NURBS shapes which I could not merge together.  For instance the plants were made out of hundreds of shapes – if I wanted to adjust their Render Stats, I would have to select each one individually in the Outliner. I did not know any other way around it.

So at the end I decided to render the Fish-bowl separately with no shadows and then render one layer with only the shadows in it and later compose those two in Nuke.

Render without shadows:

The shadow only:

Composition done in Nuke, using mostly basic nodes like Grade and Merge.





No comments: