The original question came up under the post of my HDR Prepper Gizmo for Nuke:

I have a question, how do you adjust your lights that are skewed and need to be formatted to fit your area lights? Do you adjust your arealights scale to match your bounding boxes? This example is kind of made for this scenario however there are many lights that are distorted and need to be flattened for your arealights. Im curious as to how your workflow solves this.

Which is a more than valid question as I have used a very simple-to-work-on example when I was demoing this Gizmo. However more than often in production the HDR’s you receive will most likely either have lights or other objects you might need to remove at the poles of the LatLong environment map.

A good example for it is this HDR map that I got from HERE:

 
All the lights on the ceiling (especially the one circled in red) would be very hard to paint out like this and you would need to distort it heavily to get it straight and map it on an arealight.

Luckily there’s a node available in Nuke, that is called SphericalTransform. With this node you can convert between different environment map conventions (Latlong, Mirror ball, etc.). One thing you can do is convert your input Latitude / Longitude map to a cubic map. Visually what you can imagine what it’s doing is that it seemingly puts you in the middle of the environment map (at the original position of the camera) and allows you to look around from that point of view. The output will be undistorted from the point of view of the camera (provided you set your output format to a square format):

As you can see in this example I rotated my input around so that it looks at the ceiling and directly at the light that I am trying to remove. Now that exact light is nice and square and very easy to paint out:

Or you could also use this handy little thingy: HDR Prepper Gizmo ;)

Once that is done you can convert it back from Cube to Lat Long map with another Spherical Transform Node. There are 2 things to watch out for to make sure it matches your original HDR orientation:

• Make sure your Input Rotation Order is the inverse of your first Spherical Transform (e.g. ZXY -> YXZ)
• Negate all the numbers from your first Spherical Transform (e.g. 90 becomes -90 and vice-versa)

You can then either make sure your alpha is completely opaque before converting it back to LatLong and merge it on top of your original or Keymix it back in in exactly the areas where you need it.

 
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Image based lighting often times simplifies getting started with a good lighting setup when trying to integrate CG into life action. Often times it’s beneficial to have the IBL sphere to just contain the ambient lights from the environment and therefore to paint out any actual light sources from the set. Those can then be used on separate lights to give the main illumination from the set lights, while the IBL sphere contributes ambient environment light. Now, if you have a lot of different environments and consequently a lot of different HDR’s it can be tedious to paint out the lights and output them after that… Apart from all the other work that needs to be done anyway (merge to hdr, stitch, match to plate, etc.). Sooo, let’s try to speed things up a bit… once again :)

//01.04.2014 Update

I was working on a Nuke gizmo that takes care of removing lights from an HDR with as little effort as possible. Upon creating the Gizmo you will be presented with a bounding box. This area should contain a light within the scene that you want to extract. Just put it tightly around a light source. If the HDR contains a light which isn’t planar to fit into the rectangle you can plug in an alpha into the “Mask” input. After you cleaned up one light you can proceed with adding another HDR_Prepper node to remove as many lights as you wish.
The Gizmo UI is divided into 3 sections:

The “Light Removal Settings” tab contains settings to ease the removal of light sources. It basically works by smearing in edge pixels of the crop area. Most of the knobs should be more or less self-explanatory. Either refer to the tooltips or watch the example demo further down this post :)
The topmost part of the gizmo deals with outputting both the extracted lights and the cleaned up HDR. The output path is the root path to where both the HDR as well as the lights will be rendered to. If you have multiple light sources and consequently many HDR_Prepper nodes in your script you can hit the “Set all to this folder” button to make all other HDR_Prepper nodes use the same output path.
The “Light Name” is the name of the output for the given light that you are removing. Therefore each light needs to have a unique name, because otherwise they will just overwrite each other. If you have multiple lights of the same type (e.g. multiple computer monitors that illuminate the scene) you can call one of them “screen” or “screen1″ for example, select all the other nodes which are used for the other screens and hit “Set selected to this name”. That way the selected HDR_Preppers will be called like the current one numbered numerically.
The “Env HDR Output” section deals with outputting the cleaned HDR. You can give it a name, specify a format of your choice and choose wheter to convolve the output or not. Once your settings are set you just have to hit “Create Env Output” and the corresponding nodes will be created with the settings you have chosen. Keep in mind that you need to have the EnvConvole Gizmo installed, otherwhise this section won’t work.

Aaaand again, demos explain it best, so here you go :) :

HDR Prepper Update (Nuke Gizmo) from Julius Ihle on Vimeo.

The gizmo itself can be obtained HERE.

(So far only been tested on Linux but should work regardless of the OS.)

Sooner or later there’s always a project where lot’s of things have to be removed. Sometimes there’s not only the quantity but also the quality of work required to get good looking results. There are probably not a lot of people out there who love doing this, but it has to be done, so here are a few snippets of tips I learned over the last few months.

The first one is rather straight forward. It can give a good base for wire removal on moving shots where the wire is also moving. First of all stabilize your shot with a Tracker or a track from Mocha. After that you can time offset that stabilized clip a few frames until the wire has moved to another spot. Now just reapply the motion that you previously stabilized on the same reference frame. That way you will have essentially pretty much the same plate but the wire being offset. Now it’s just a matter of painting and keymixing to get a good base for a working wire removal.

The second one requires a bit more work. It’s pretty useful for wire removals aswell. You first of all need a proper set geometry of the shot you are working on aswell as a matchmoved camera. As soon as you got both into Nuke just go ahead and project the framerange through the moving camera onto the setgeometry. Pick a good frame where you can see most of the range you need to work, freeze the camera at that point and use it to render the sequence through a scanline renderer. What you now have is the whole sequence which is properly stabilized. If there is a bigger camera move and you want to get access to the whole stabilization you can add a crop below the renderer to ensure you encompass everything you need. At this point you can do a comparatively easy cleanup on your stabilized shot. To get back to your actual movement from the shot just your cleaned up stabilization through the frozen camera from before back onto the set geometry and scanline-render it through your shot camera. The description might be a bit cryptic, so here’s a quick screenshot which probably gives a better visual sense of what is going on :)