Document: HTOL4Indoors Link: https://www.horo.ch/docs/mine/pdf/HTOL4Indoors.pdf Hypertexture Obscure Light for Indoors Obscure Light - as developed by David Brinnen - essentially works with an HDRI from inside and a True Ambience optimised radial with a diffuse gel surrounding the scene. Instead of the HDRI a Hypertexture can be used to light an enclosed room. Preamble The Obscure Lighting method (OL) can be used to light an enclosed room successfully if the True Ambience (TA) optimised light source is set within the room. A TA optimised light source is not a point light source anymore but an area light source where the perimeter shown in the wireframe is usually that surface or area. The larger the area, the more light generated. The classic OL method uses a TA optimised light source that is lit by diffuse (HDRI Effect) from an HDRI from Inside. Instead of using an HDRI, a Hypertexture (HT) can be used to drive ambience for the light source instead of diffuse. There is a video and a transcript that describes the classic method using different TA optimised light sources driven with by a diffuse gel from an HDRI from inside. An HT can be used in the Materials Lab to boost the output beyond the usual value. The newer Phased Hypertexture (PHT) does the same but is easier to use, the output can be calculated and easily be made negative. It can be created in the Deep Texture Editor (DTE) with a few clicks. Here it is used to boost the Ambience output to make ambience not only glow but shine, replacing the HDRI for the classic OL. Sky Settings and Light Source As far as the Sky settings are concerned, there is only the global Ambience that must be set to fully white. It is your choice whether you want Fog and Haze in the room. If the room has windows to the outside, you may want to set sky colour, sun and clouds. The sun light shining into the room will also change the light in the room to some extent. [Picture] The only light source to be used is the new (yellow/green) Square Parallel Light, above identified with the number 3. It is the only Bryce light source that has a rectangular sheet that shines both ways when used TA optimised. [Picture] TA sees a sphere for all other new light sources. The legacy parallel light (yellow) is not truly parallel and if used as will be shown here, there is no light. The Parallel Light is actually a sheet of light and Y can therefore set to 0 as shown above. <<<< Page 2 >>>> [Picture] There is not much to set in the Light Lab. Infinite Width and Direction control both have no effect, neither Diffuse nor Specular. Just enable True Ambience Optimization, Use Gel and click on Procedural to enter the Mat Lab. Set a dot for channel A, B, C or D for Ambience and get a PHT (one component with Phase 500 is usually good) and set Ambience to around 10 for a start. Make sure Ambient colour is fully white. This is the start setting for one indoor light source. More may be added with somewhat different settings. Render Setting [Picture] <<<< Page 3 >>>> The Rays per pixel can be set lower to speed up testing, for the final render, 64 may not be enough. Boost Light may be used to get more light output but since it is just a click away, try your scene with and without this option. Flaws This is a simple room: a cube 200 BU wide (X) and high (Y) and 500 BU deep (Z) with default grey and a sphere in the centre and to the right, touching the floor and the right wall. It has red diffuse at half brightness (127). There is only a single Square Parallel Light with exactly the same size as the room: 200 by 500 BU, positioned at half height. Bright Line The room at left can be lit a bit brighter if a two component PHT is used, but only by 10%. The centre room is 80% as bright as the left one. With Boost Light enabled, the room at right could be set to fully white. [3 Pictures] The light sheet shines in two opposite directions. The red sphere is lit from the light shining down and the colour only bleeds downwards in this case and no colour bleeds through the light sheet upwards. If the sphere is moved up and cuts through the light sheet, there is colour bleed on both sides but on each side only half as strong. As shown above, there is a distinctive horizontal brighter line where the light sheet meets the walls. Below, the light sheet was rotated vertical. [3 Pictures] The render settings are the same and the bright line is now vertical, also the colour bleed is restricted to one side. On the left example, the flaw is worse because the right side is obviously less bright. This seems to be a TA flaw when using a strong PHT setting to boost the light. We would expect to get the left wall darker when the light sheet is turned to the other side, but it can be rotated X or Z by 180° and the darker wall stays on the same side. If the camera is banked, the darker wall moves with it. If the camera is set to the far wall and looking back, the sphere and the colour bleed move to the left but the darker wall is still on the right. The light can be moved off centre or rotated a bit, the dark wall remains on the right. <<<< Page 4 >>>> This odd behaviour is visible in all renders with the light sheet vertical but only very obvious if the PHT boosted Ambience is very strong. Dark Line The good news is that if the size of light sheet is enlarged and goes beyond the walls, there is no change in the intensity of the bright line. If the light sheet is smaller than the room, the bright line will change to a dark one that is even visible if there is a gap as small as 0.05 BU. This line gets thicker and darker the wider the gap is. [3 Pictures] All renders are with Ambience 12 and Boost Light enabled, like the right images on the previous page. For TA, the size of the light source determines the brightness. The render at right is darker because the light sheet is only half the size of the room. It can be compensated by increasing Ambience or Phase for the PHT but the room stays unevenly lit. [Picture] Looking at the render at right it would seem that using a horizontal and vertical light sheet, both half size of the room, would get rid of the dark line. But if the light sheet is almost the size of the room with only a small gap to the wall, this does not help, the thin dark lines remain and instead of a horizontal or vertical one, there are both. Besides, the light sheets are still small and light only half the room. Remedy Actually, there is none. The dark line is more offending and the easiest way in most cases is to make the light sheets go beyond the walls and cope with the bright line. [3 Pictures] All three examples hide the bright line. The light sheet was moved up to 1 BU below the ceiling. At left, we have a glowing ceiling and some light in the room, a bit dark. In the centre the room is brighter lit but the ceiling is blindingly bright. At right, the same setting like at left but additionally there is a vertical light sheet on the back wall with Ambience set to 27. This for the camera invisible light is very bright; the walls and the ceiling get a wee bit of the red colour from the sphere. Although the bright line is invisible, the above examples are not really a satisfactory solution. <<<< Page 5 >>>> Filters The brightness depends on the distance of the light source to an object. Sheet lights moved near the walls, ceiling and floor brighten them up much more than the rest of the room. The ceiling above is excessively bright because the light source must be strong to light up the room. A work around is to use a filter between the wall and the sheet light. A filter is a 2D-Face with transparency lower than 100%. In all these examples there is a space of 1 BU between the light and the wall, the filter is placed between them. [3 Pictures] At left, the ceiling light has 15% Ambience and the filter Transparency is 70%. The ceiling is only moderately brighter than the walls and the room is nicely lit. For the centre render, there are additional sheet lights and filters on the left, front and back wall. None on the floor and at the right wall, otherwise there are no shadows. The same settings were used at right but a simple material applied to the room cube. From the brightness of the sphere it is evident that the light comes from above, from left and from the back of the camera. There are no white lines visible. To make this room believable, it must be set less bright and a visible light positioned that provides the key light. Then, the rest can be considered being ambient light. [Picture] In the example at right, the Ambience setting for all light sheets used was halved and a simple lamp introduced with a radial high up in the green shade with linear falloff and 25% soft shadows. Note that the filters also dim the light from the radial. The filter between the sheet light and the wall is a two way light attenuator and outside light is also dimmed before reaching the surface. Luckily, it also "eats" some of the noise. The less bright an object is rendered by TA the noisier it gets and a filter helps supressing much of that noise. Example 1 [2 Pictures] <<<< Page 6 >>>> The example above shows the Classroom Scene by Rashad Carter with all his elaborate light setup removed. There are three light sheets and two filters. At the ceiling with a filter, at the right wall with a filter and behind the camera without a filter. At left, rendered without Boost Light enabled and Ambient colour white. At right, rendered with Boost Light and the Ambient colour mid grey, resulting in half the light emitted by the light sheets. The left room is lower contrast, the right one with high contrast and more saturated colours. Both rooms look plausible at first glance but considering all the light comes from outside through the windows at right as indicated by the sunlight hitting the floor, the brightness distribution is not correct. The right wall ought to be darker and there is too much light coming from the ceiling, more prominent in the render with boosted light. In this respect, the left render is a tad better. Nevertheless, this scene could be made more plausible if the ceiling lights were switched on and the ambient light from the light sheets reduced. Lighting a room exclusively with light sheets is not the best solution. However, if mixed with conventional lights and using the light sheets only to provide the ambient light may prove simpler than using several Dome and/or Fill lights and render regular without TA. Example 2 [4 Pictures] The building is Faded Industries by Stonemason, at left lit by 8 yellowish radials as tungsten lights in lampshades hanging from the ceiling and 6 blueish radials making the light of the fluorescent tubes, which are higher up. The ceiling is black because there is no light, only the sky shines through the windows in the roof. At right, two horizontal sheet lights were added, one just above the tungsten lights and one, slightly brighter, above the fluorescent lights. The difference between the upper and lower images is only the camera positions, which are roughly opposite. The images at right were rendered TA with only 16 Rays per pixel (rpp). <<<< Page 7 >>>> Example 3 Using sheet lights and filters - if appropriate - and rendering with TA is a means to give the room ambient light. This does not mean this is the only or the best method; however, it is easy to set up, balance and renders relatively fast. If the room is bright overall and there is some bump, a lower (rpp) setting can be used as shown above. If the room is relatively dark, even 256 rpp may prove to be hardly enough. [2 Pictures] The room at left is lit only by three radials set into the lamps. An IES (Illuminating Engineering Society) Area Light gel is applied to the radials which gives the light pattern on the walls. Obviously, the ambient light is missing. At right, a Square Fill Light with 200 light sources, all with soft shadows like the radials, provides the missing light and a single radial without shadow casting at the camera position helps to light floor and wall under the table. Both rooms were rendered Premium with Soft Shadows and 144 rpp - the left one six times faster than the right one. [2 Pictures] Here is the alternate method to supply ambient light to the room. Instead of the Square Fill Light and the radial at the camera position, two light sheets were used: one at the left wall and one at the back wall. None of these two walls are visible in the render and no filter was necessary. Both are only half as high as the room, the one at left also only half as long to assure that the left side of the wall in front does not get too much light. The left render is TA, the right one has Boost Light enabled and the light sheets only half as bright as for the left render - though obviously still a bit too bright. Both had to be rendered with 256 rpp because of the noise on the wall below the table. Nevertheless, both needed only 25% longer to render than the one with the Square Fill Light at only 144 rpp. Apart from the slightly different overall brightness, the three renders look quite similar, except for the blurred shadow of the left table leg on the wall. This suggests that there is a light at the back of the observer. <<<< Page 8 >>>> Example 4 It is also possible to make clay renders, a bit like ambient occlusion (AO). Level 19 by Stonemason without textures and lights. Two light sheets, a vertical one behind the camera and a horizontal one at half height through the room. There is a third and smaller vertical one to brighten up the alcove at the back at right. Moving the horizontal one a bit lower so it covers the alcove, it gets too bright and the feeling of distance gets lost. Without the small addition, it is too dark. [Picture] Conclusion Using a Square Parallel Light as a light sheet to create the ambient light - simulating part of the reflected light from other objects in the room, and the air - is a relatively simple and easy to use method. Lighting indoors is often more challenging than lighting an outdoor scene. It is good to know that there are several methods to accomplish the task. A preferred method may suit this scene but not the other; luckily, there are several possibilities to tackle the challenge. Bryce never ceases to amaze - even astonish - me with the tools it offers to the artist. A beholder of a render may scrutinise it to find flaws that show that the image is not actually natural or fully plausible. However, each artist wants to convey a mood with his or her artwork. No matter what software you use and what methods you apply to make your artwork look natural and plausible, it will always be a hack. There has been great progress in software to help in the endeavour to create plausible, natural looking artwork but this comes - unfortunately - at the expense of the freedom for the artist to express him or herself. In this respect, Bryce is truly software for the artist. Bryce Primitive 3D Shapes When using the camera inside a cube, sphere, cylinder, pyramid, cone and light the "room" by TA in the manner discussed here, make sure that in the Mat Lab the Volume colour is fully white. If it is black, the inside will always stay black, if Volume colour is red, for instance, then the room will render red. This is not the case if the room is built with 2D-Faces, cubes as walls or any mesh shape made in another program, like Wings3D. Links The classic Obscure Light method: * Video #14 in the list https://horo.ch/docs/video/horo_en.html * Direct link to YouTube: https://www.youtube.com/watch?v=1BYsfGR4sBU * Link to the transcript: https://horo.ch/docs/video/pdf/Transcript_OL4Indoors.pdf How to create a Phased Hypertexture in the Bryce Deep Texture Editor: * Phased Hypertexture (PHT): https://horo.ch/docs/mine/pdf/PhasedHT.pdf November 2017/horo