Integracion

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Integracion

  1. 1. Q&A | Matching real-world lighting references Q&A SOLUTIONS / FIXES / ADVICE QUESTION OF THE MONTH Submitted by John Spyder, via email 3DS MAX “How can I light a CG model to match a real environment?” This issue’s solution is supplied by the UK-based author and help out. The key task during scouting is to note down the positions VFX animator Pete Draper. More of Pete’s tutorials can be of lights and objects in the environment in relation to one another, FACTFILE found at www.xenomorphic.co.uk, his personal website and determine if there will be any problems later on. If this is the FOR first time you have done this, don’t bite off more than you can chew. 3ds Max his question relates to one of the fundamental Try to avoid having a lot of things in shot that you will only have to DIFFICULTY Advanced TIME TAKEN 1-2 days (including location recce and shoot) ON THE CD T challenges of VFX lighting: integrating a CG object directly within a real-world backplate. In this Q&A, we will explore the process of collecting data on a live shoot – in this case, of an underground car park – then using this data to reconstruct the environment in 3D and to light a model of a mask out later on; and stick to open spaces, so you won’t have to deal with a lot of objects receiving shadows from your CG model. If you can, visit the location at the appropriate time of day beforehand, so you can see if there are any contributing factors – such as drunks or joyriders – that will make your life more difficult virtual object (a giant mech robot) so that it matches the real when it comes to shooting. On the day, you really want to get in, do • Full-sized screenshots • Reference photos location exactly. The walkthrough assumes that you are already the shoot right first time within controlled conditions and get out. • 3ds Max scenes familiar with 3ds Max and basic visual effects concepts, so if you’re The next step is to bring all of the information you’ve recorded • Mech model, courtesy a beginner, try the other tutorials in the magazine first. into 3ds Max. If you’ve taken down decent notes, you should be able www.3D-Palace.com Not all of the considerations discussed here – such as whether to recreate a basic to-scale replica of the real environment that your ALSO REQUIRED the environment is interior or exterior, or whether it’s day or night – CG object can interact with. You will then be able to position your HDR Shop (free from will apply to your own shoots. The basic rules, however, always hold CG camera in exactly the right place, set up virtual lights to match www.hdrshop.com), Photoshop true: scout the location during daylight hours; take as many the real ones, and drop in your CG model at the correct location. measurements as you can; and call in as many people as possible to Easy, eh? Let’s give it a go … 070 | 3D WORLD November 2006 TDW83.qa_lead 070 29/8/06 11:04:10
  2. 2. Matching real-world lighting references | Q&A STAGE ONE | The location shoot First of all, you need to source a location for your Once you have found your location, take enough By the end of the recce, you should have enough 01 shoot. When you do this, you need to consider its 02 measurements to allow you to recreate it in CG later 03 information and taken enough notes to be able to aesthetics at all times of the day, and see if you can on. Think outside the box: in the car park, many of faithfully reconstruct at least the basics of the physically get the shot that you want well in advance. You the structures are mass-produced, so most of their environment. Because you have done this during the day, you really need controllable conditions, so the light and objects in measurements (for example, the pillar bases and the can always rough out the scene before the night shoot, which shot do not change. distances between them) are identical. Get as many will flag up any measurements you may have missed. measurements as you can during the day before the shoot. For the shoot itself, try to rope in as many people as Ensure that the position of the camera is noted and Next, take reference shots from exactly the same 04 possible to help you out – with the promise of drinks 05 measured in-scene, and record the height of its CCD 06 location, using the same camera settings. First, take afterwards. You need to get in and get out as fast as above the ground. When taking the photos, make a photo of a white ball (see Step 9) in the position you can. Take any final measurements that you couldn’t sure that all variable features (such as shutter speed, ISO and your CG object will eventually be located. You can set up a CG collect earlier, while the location was busy. For best results, focus) are locked. If possible, take the pictures with a remote version of this ball in your 3D version of the environment to it’s advisable to use a digital SLR camera, so that you can or use the camera’s timer so that you don’t nudge it when check that its lighting matches the photo exactly. (We won’t shoot and review pictures as quickly as possible. pressing the shutter. First, take your wide backplate shot. do so in this Q&A, but it’s good practice to collect the data.) Next, replace the white ball with a chrome one, and The close-up of the ball is the key to this process, Finally, measure the height of the pole each ball sits 07 shoot it in exactly the same position, first from a 08 since you will encase your 3D scene with an 09 on, so this can be recreated in 3D. The balls distance (so that you can match its position in the 3D unwrapped version of the image, to give the CG themselves are quite easy to obtain – chrome ones environment), and then in close up. This will allow you to set objects something to reflect. If you can’t zoom in enough to can be obtained from garden centres (normally called ‘gazing up reflections on the surface of your CG object so that they fill the frame, tentatively move the camera forward and zoom balls’), and come with a hole in the base for fitting. The ‘white’ ▲ match those of a reflective object in the real environment. in: you are trying to reduce your own reflection in the image. ball is a large Christmas ornament, spray-painted 20% grey. November 2006 3D WORLD | 071 TDW83.qa_lead 071 29/8/06 11:04:18
  3. 3. Q&A | Matching real-world lighting references STAGE TWO | Creating the virtual environment Use your measurements to mock up a simple 3D The next task is to create the virtual camera. You Bear in mind that you are mainly using the 3D 10 version of the environment. We’ve done this for you, 11 may need to convert the lens values to 35mm 12 versions of the background objects to receive so open carpark_lighting_start.max from the CD. equivalents to dial them into 3ds Max. Use Show shadows; masking out CG objects behind pillars will We’ve assigned a Matte/Shadow material to the entire scene, Safe Frame to ensure the render output is the same size as take additional care and attention. Next, create a virtual and set each object (apart from the lights) to receive shadows, the viewport image. Use your measurements to position the representation of your chrome ball in situ according to your but not to cast them. The remaining steps also rely on our virtual camera at the same point in the scene as the real one, measurements: again, this should line up with the backplate own data, but you can copy settings from the screenshots. and tweak it until the 3D scene aligns with the backplate. as illustrated in the screenshot above. To simulate accurate reflections on the CG objects in Open HDR Shop (free from www.hdrshop.com) or Save the resulting panoramic image as a bitmap, 13 the scene, bring the close up of the reflective ball 14 any other software that allows for spherical to 15 ready to load back into 3ds Max. For now, you are into Photoshop. Using the Elliptical Marquee tool, panoramic distortion. Load in the cut-out of the ball only going to be rendering out the scene in a single drag out from the middle and select the entire ball. Select you just saved, and accept any settings. Next, select Image > pass (you would use more than one pass in real visual effects Edit > Copy, then go to File > New and accept the settings. Panorama > Panoramic Transformations. In the resulting work), so you need the background to render as well as the Finally, on a black background, paste the cut-out ball into the panel, tell the software the source and destination types, CG mech. Additionally, you need to reflect adjacent CG objects new file. Save out a flattened version of this new image. namely Mirrored Ball and Latitude/Longitude respectively. in the scene that you will introduce later on … Therefore, you need to add the Latitude/Longitude One task you can complete now is to clamp off the To test out the reflections, add a basic 16 reflection map into the Environment slot of a Raytrace 17 colours of the map and boost its white value, by 18 reflective object to the scene. Normally, this would map located within a material assigned to an object in amending the map’s Output curve as shown above. be a CG version of the chrome ball. However, as the the scene. To make life easier later on, you can just instance This is so any reduced-intensity reflections (such as those white car is more prominent in the backplate, we have this Raytrace map throughout your scene’s materials as using Falloff maps or created by reducing the value of the designed a basic material that mimics white spray paint and required, in case you need to tweak settings such as brightness reflection in the material’s root parameters) still have white assigned it to a teapot primitive (used because it contains and blurriness later. highlights. These are, in fact, reflected specular highlights. virtually every type of surface). Now for the lighting … 072 | 3D WORLD November 2006 TDW83.qa_lead 072 29/8/06 11:04:24
  4. 4. Matching real-world lighting references | Q&A STAGE THREE | Lighting the scene The first set of lights to establish should be the key With the lights in situ, tweak their settings. Because The next set of lights should supplement the key 19 light or lights in the real environment. Here, these 20 there are CG objects close to them, you need the 21 lights. If there aren’t any in the real environment, are the lights along the ceiling. As you are simulating illumination to behave realistically, so use Inverse concentrate on setting up secondary lighting. In an area lit with standard lights, use several instances of a Square decay. Shadows should be diffused because of the the final scene file on the CD, we’ve set up the next brightest single light to create the impression of an area light shadow. light type, which will hide banding created by overlaid shadow objects in the scene: the pillars. There are several low-intensity First, position a single light, then instance it to create the maps: this is done by increasing the shadow’s Sample Range. lights with diffused shadows, attenuated and with no specular remaining lights in the scene, as shown in the image above. The lights’ colour is derived by point-sampling the backplate. highlights. Each light’s colour is sampled from the backplate. Contact us | Send your Q&A questions to 3dw.qanda@futurenet.co.uk The final set of lights to establish are general 22 attenuated fill lights, which we have positioned above the ceiling and beneath the floor so that there is some ‘bounced’ light in darker areas. As these are subtle low-intensity lights, designed purely to bring out areas of illumination from secondary or tertiary bounced lighting, they need not cast any shadows. With the final test render complete using your To see all of the final settings, load carpark_ other locations – particularly if the objects present in the 23 stand-in teapot, replace the object with the mech 24 lighting_finished.max from the CD. The final image scene and the reflections differ visibly. Ideally, you should model (provided by www.3D-Palace.com). Merge has a few additional instances of the mech scattered shoot additional reflection references for each CG object at (or XRef) in Dummy_ATMT and its child objects from the throughout it. These are positioned carefully with respect to the position it will appear in the scene, especially if you’re 3dpalace_atmt_mech.max file on the CD. Using the Align tool, the key lights for two reasons: illumination and reflection. planning to tuck it behind background geometry. The pillars reposition the dummy object to the position of the teapot, Because the reflection image you shot earlier was designed won’t be reflected correctly in the shiny surfaces of a mech and re-scale the dummy so that the mech fits in the car park. to be used at a single position in the scene, it won’t work at unless you have the corresponding reflection image. ● November 2006 3D WORLD | 073 TDW83.qa_lead 073 29/8/06 11:04:31

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