Tag: Background

Since the Poser virtual world can’t be filled with objects to infinity, I’ve got two ways to define the far away portions

• A background shader – this chapter
• A defined object with a color or texture (usually a photograph) attached – next chapter

The background shader

As light rays travel from all lights via all objects onto the view plane of the camera, some pixels will hardly, or never, get lit. This is where the “background shader” kicks in, and fills the emptiness. The Poser background shader can be set for the Background notion in the Materials Room. Background is not an object, like the atmospheric Volume is not an object either.
 

 

The actual working of the elements is a bit confusing, as you can see there are

• The “Current BG Shader” of Background root node (root nodes don’t have an output connector at their upper left)
• The BG Color node
• The BG Picture and BG Movie node
• The Black node

Now I’ve got the Preview and the Render, and the question: which one is showing what?

The Preview is arranged for in the Display menu:

When an image is loaded into the BG Picture node, either by assigning one as the Image_Source parameter or by loading one via the Import \ Background Picture menu option,

the Show Background option in the Display menu becomes available. That is: the BG Picture node should be connected to the Color parameter of the Background node. Then, when the menu option gets checked, the picture is shown in the preview. The image, and hence the content of the Image_Source parameter in the BG Picture node can be deleted by using the Clear background Picture menu option.

A similar scenario holds for displaying a movie in the preview: load one in the Video_Source parameter of the BG Movie node, or import one via the Import \ AVI Footage menu. The Show Background Footage option becomes available and can be checked. Again: the BG Movie node should be connected to the Color parameter of the Background node.

When nothing is checked, or the checked Picture / Movie option is not connected to the Background node, you’ll get the BG Color node contents in the preview, whether it’s connected to the Background node or not.

The Rendering is arranged for in the Render Settings:

The first three options pick the contents of the BG Color, the Black and the BG Picture node, the latter has to be connected to the background node’s Color parameter. The last option: Current BG Shader, picks up whatever is connected to the Color parameter, and multiplies with that color swatch too!

Again:
In Material Room I’ve got the background root node, and four basic nodes: Black, BG Color, BG Picture and BG Movie. I can connect any of these to the Color channel of the Background node.

In the Display menu, I’ve got options like Show Background Picture, Show Background Footage and Use Background Shader Node. Only when the BG Picture node is connected with Background, the Show Background Picture option becomes available to turn showing the background picture in the preview on/off. Only when the BG Movie node is connected with Background, the Show Background Footage option becomes available to turn showing the background movie in the preview on/off. The Use Background Shader Node menu option has not shown any effect on anything up till now. Sorry for that.

From the File menu, I can Import either a background picture or background footage. When importing Background Picture, Poser loads the BG Picture node, connects this node with Background (hence dims the Show Background Footage option) and switches Show Background Picture to ON. When importing Background Footage, Poser loads the BG Movie node, connects this node with Background (hence dims the Show Background Picture option) and switches Show Background Footage to ON.

Do note that I can set the BG Color from the Document panel directly, using the (second) color-swatch option at the bottom-right. So, for handling backgrounds, I don’t have to enter Material Room at all.

In Render Settings, I can select the render background almost independent of my choices for Display, or the node-connections in Material Room. That is: I can render against Black or Color even when the preview is showing Picture or Footage, with Picture / Movie node connected and the Display menu option switched ON. I also can render against Picture or Footage while the preview is not showing it, having the Display menu option switched OFF. But in order to use Picture or Footage in either preview or render or both, the corresponding node must be connected to Background in Material Room. To the Color swatch.

The other way around: how to rotoscope against a movie.

First, I go File > Import > Background Footage. This will load the BG Movie node, connect it to Background en switch ON the Show Background Footage option in the Display menu, so the footage will be visible in preview.

Then, in Render Settings, I have to select Render against: Background Picture (or Current BG Shader), and the footage will appear in the render results as well. That is: provided I use a save / export format without transparency: a series of PNG’s will not show any background anyway!!

Next >>

Instead of filling the empty space and non-rendered pixels in the result by a background image, I can put objects in the scene. From simple planar billboards or screens like the backdrops in a real-life photographers studio, walls of a room, to varied setups representing outdoor scenes with more depth. Cycloramas, dioramas, environment balls and more – supported with additional partial billboards and images with alpha channels – all serve the purpose of building a partial environment in the scene.

The one question that comes up every time is: what’s a proper size for images used on those backdrops? Simply stated, the amount of pixels that can be seen on the result should be at least twice (and at most four times) the amount of pixels in the result itself. This has to do with texture sampling and pixel processing statistics, a simple one-to-one ratio might result in loss of quality. As Poser puts a 8192 limit on texture sizes, this implies a 4096 limit on good quality render results – as far as backdrop images are concerned.

And what about full 360° environments like a sky dome?

Consider a camera at normal lens settings, that’s 35mm focal length and 40° Field of View (see table below), taking a shot (render) of say 2000 pixels wide. The full sky dome, 360° all around, then would require 360/40 = 9 times my view. And as good texturing practices require at least double the resolution of my render, the sky dome should be assigned a 2x 9x 2000 = 36.000 pixels wide texture, at least. Note that Poser takes 8.192 for max texture size, and you know you’re stuck. Note that the size of the sky dome – or any other 360° environment – does not matter. The Field of View matters, as a shorter focal length (typical for landscapes, say 20mm) increases FoV to 60°, and reduces the required texture to a 2x 360/60 x2000 = 24.000 pixels width.

Focal length (mm)	10	20	30	35	40	60	90	120	180
Field of View (°)	90	60	45	40	30	22,5	16	12	8

So the bets are that you’ll end up with say 8000 pixel wide panoramic image for the sky dome, which is too low a resolution for proper background imaging, plus some background image prop holding another 2x 2000 = 4000 pixel wide portion of the high-res version of the panorama just covering the left-to-right edges of the rendered view.

Object versus Shader

Using a background object instead of a background shader (picture, footage) does make a difference.

• * In order to make proper use of atmospherics, Volume as well as Depth Cue, I do need a background object. Atmospherics don’t show against voids, even not when they are textured using a BG Picture.
• * In order to make proper use of Depth of Fields or: focal blur, I do need a background object. The background shader will always be presented sharp, as it replaces empty space. This might give gradually blurring objects against a sharp background, so weird. But of course I can use a blurred background picture for shader, which then remains blurred in renders without Depth of Field set.
• * Wherever you turn the camera to, the background shader image will always be the same. Great for stills but not for camera-moving animation.

Not every picture can or should be used for background under all circumstances: it should match the scene, or the other way around. The first issue usually is: brightness, contrast, saturation or: light and color intensities should match. The second issue then is: shadowing. Both issues are best addressed by a complex balance of lighting (position and intensity), materials, sometimes even atmospherics and pre-processing the background image or footage. And please do note that shadows in a background image do suggest the positions of the main lights, so you might have to flip the image to establish a match with the lighting in the scene. And please turn off shadow casting for the background object itself.

Other material aspects “just depend”, usually they are absent. No specular / highlights, no bump let alone displacements, no reflection nor transparency or translucency. But when the background represents a real wall, it just might benefit from specular, highlights and some bump.

Perhaps the backdrop object shouldn’t even respond to Indirect Lighting (switch off its Light Emitter property then), or the other way around: it should emit light from its Ambient channel to compensate for blocking the environmental lighting from a sky dome.

There is no single best way, but perhaps these notes might serve as a checklist. Happy Rendering