Wednesday, September 23, 2009


Hello bloggers,
It would be good to finish off the blog with final images of your projects.
Also, as it looks like I might be doing this blog next year, please post any feedback or constructive criticism.
Look forward to the last posts.

Wednesday, August 12, 2009

RE: Nigel Architectural Visualisation

Hi Nigel,

It is good to see an update, I hope you're not too exhausted and have enough energy for the final push. You can relax, after the hand in ;)

It would be a shame to lose the outside by blowing it out so much that you can't see it, and it would take away the point of having a moving camera to show off the panoramic view. Equally it makes no sense to have full sunlight falling into room and for it to still be dark. What you are trying to achieve makes far more sense when you see your photo reference from your previous post, but as I said in my reply, this lighting is physically too different to make it work with your current scene. This is definitely something to reflect upon for next time.

Here is the reference again from the first image. They both show interior and exterior and so are a good reference for your project, especially how they get it to work without the outside blowing out.

It's warm, light and bright, the lighting might not be realistic, but it is believable, and more importantly it sells the house.

We have had a few discussions on volumetric lighting, in Jamie and Lies recent posts, which you should read because it is relevant.

A depth pass can be used to add atmospheric lighting, but used on an interior, it can make a place look dusty and dingy and is often used in the thriller genre (see the Citizen Kane reference from Jamie's RE:) , and the same with volumetric lighting so I would re-think its use for a show home project. Outside you would normally only see the effects of a depth pass over large distances or as ariel perspective (colour change over large distances or to show rain or fog.

The yellow grade you have added is warming, but it feels a little on the green side (it could be my monitor). I think that it would be better on the orange/red side and a bit more saturated. I have done a quick paint over and grade of your image, it is by no means perfect, but I want to show you a less dusty warmer colouring. I have also limited the glow/burn out to the top left side of the window, to give it a bit more direction, and contrasted up the image to get the hot highlights on the floor. When you are working in comp, be careful to not loose the colour in your feature items. The light glowing off a red object such as the sofa is what adds the pizazz you need.

As a general rule, its better to try and fix rendering problems at the source rather than trying to cover them up. If one part of the model is blotchy there is a good chance that it will occur somewhere else. Did you bake out the lighting in the end? I believe the blotchiness is because your settings are not quite right yet, I have seen it before. Look on the forums for help, I think these might be useful.

There is no problem using your comping fix, but just be aware that this is not the ideal solution and if you had the time it would be better to change the settings.

I hope this helps, good luck finishing off.


Tuesday, August 11, 2009

RE: Yoli take 5

Hi Yoli,

I much prefer your new renders, I like the fact you have used reds and greens and yet avoided looking christmassy. I think I understand the nostalgic look your after and hopefully I can give you some tips, to help soften it.

Normally I wouldn't recommend changing your reference 3 times :) but I think that you have come up with something much more unique for your showreel. I hope that you are happier with the end result. It is much more endearing than what you started with.

The direction of your key light is not immediately obvious. You will not see a shadow that faint and that sharp in the real world. Faint shadows tend to be soft occlusion type shadows rather than the key light shadows. I like to think of the fill light as the base lighting, you add the key light on top to add depth to the image. If you do have shadows but can't see them, it's because your fill light is too overpowering, and your key light is not intense enough. This is a common mistake by lighting beginners, possibly because students automatically think that lighting is about being able to see everything and therefore make all the lights the same intensities. The result is flat looking CG images. If your not sure what a light is doing, or where a particular light is coming from, look at it in isolation. Black patches where there is no fill and no key light look ugly, perhaps use an ambient light to bring up the black spots, re-place your existing lights (or re-think the type of light) or add an extra light (perhaps a subtle bounce light).

Observe my quick renders and comp (ignore the shadow direction, this is inherited from someone else's post).

The key light adds the drama, the more contrast there is with the fill light, the more depth your image will have. As you have a flat background you have no other way of getting depth into your image other than with lighting. I have used a greener blue for the fill and a orangey yellow for the key. The blue is a warmer blue, combined with warm key, the overall impression is of warmth and softness. The strong key light also directs the eye to your subject, see the reference again for inspiration.

I took old reference, most of it over 100 years old, because although computer lighting is a relatively new subject, the concepts and traditions we use are very old and well established. There is no point trying to do something new, until you have studied the past. I recently went to the Banksy exhibition at the Bristol Museum near where I live. My favourite piece is a big stone with some words engraved on it. "The bad artists imitate, the great artist steal." below it, Pablo Picasso is crossed out, and Banksy is inscribed :)

The only way you can literally soften an image is by either softening the edges, which would only look right if your objects are moving (motion blur) or depth blur (and you have no depth), or by softening something in the images, ideally the shadows. It only needs a tiny amount of shadow blur to soften the whole image, see the image below where MR shadow blur is set at 0.002. Also make sure you use your occlusion pass to get those realistic soft occlusion contact shadows. This will help bring the whole thing together.

I personally wouldn't use an incidence shader as a rim light, but it does a good job of making the character stand out from the background. I would try to keep it a little more subtle, and perhaps tinted a cooler colour to contrast with your warmer key light.

Don't feel that you need to have a central composition, I think it is more interesting slightly off center. You will need the stronger lighting to direct the eye, and then add a vignette to frame the image. As a final note, re-read the other posts, ones to Lies and Holly, as well as the shadow extract, should be particularly useful to you.

Good Luck finishing off, I hope have time to make some changes before the final deadline.


Nigel Gore - Rendering & Compositing

Hi Tessa,

Thank you for all of the feedback in your last post, it was very helpful.

Since then, I have been working around the clock to get my passes rendered out.

I am now in my final stages of rendering and the main problem that I have encountered is a strange ‘blotchy’ effect on the wall above the windows which seems to be a result of the final gather calculations from the appended file:

I am now creating a new pass that I can ‘comp in’, to hopefully reduce this effect:

I have now started to pull together a few composited scenes in Nuke. I started by trying to make the sunlight appear to be glowing around the window frames:

I’m still trying to show how the scene would look if the interior lights were also switched on. My initial attempt resulted in the room actually appearing to be darker:

I’m much happier with my latest attempt, where the interior begins to look much brighter & whiter than before:

I have also created a Z-depth pass. It is applied to this frame… However, I have not yet tweaked it enough for it to look very convincing:

Here, I have added ‘volume rays’, to simulate sunlight piercing through the scene… I like the effect that it has on the TV screen but not so sure about the other areas. Perhaps it just needs colour adjustment or to be more subtle:

This will probably be my second to last post because I have a very limited amount of time to make any changes. I’m looking forward to your thoughts on what you have seen so far…



RE: Jamie's First Comp

Hi Jamie,

Sorry for the late reply.

Great work! I think you have the lighting side pretty much wrapped up, I will only say that you should watch your hot spots on the horses, they are clipping a bit too much. The white horse is reflecting light 'like metal' in places, you loose the detail when it is burning out plus it is a bit distracting from the overall model. I would consider wrapping the key around a tiny bit more to accentuate the lighting on the model.

I really like the idea of using atmospheric lighting for this kind of project. The way you have it set up at the moment looks more like a lens flare than god rays, I actually think that in this instance, a lens flare would be a perfectly good way to achieve the same effect, so maybe do some research into this. The position of the bright hole in the clouds means that the god rays have nothing to contrast against, before it meets the character, see the reference for examples. Also it's not really working because of that particular angle of the light, and the fact that it is probably a bit too subtle. If the background and framing were different, perhaps for different shots, I am sure you could get it to work, to achieve the mood you are after.

When I look at your image, the overall impression is great, its atmospheric, it has drama, but it is being undermined by the strong depth blur on the distant trees. It gives the illusion that the model is small, rather than the true scale of men on horseback, and I think that it is compromising the epic nature of your pose and lighting. That amount of blur would work on a close up, but not a wider shot. If you are going to use depth blur on your images it is best that you have a basic understanding of cameras. I am no expert but I have put together an example, to show you what I mean.

I used a Canon 350D, focal length of 23-mm ( I am using a wide angle lens on purpose) and f-stop 4.5 to take the pictures below . The only variable is the distance of the subject, my WALLE toy, to the camera. The nearer the focusing object is to camera, the shallower the depth of field (DOF is the area in focus). Notice how close the object is, to get the background to blur extensively [that is my arm and I am looking through the viewfinder at the same time]. Try using this calculator to see it in numbers ...

With these settings, the subject only has to be 6.5 meters away for the depth of field to be infinite. Therefore the blur would be over a very big distance, and would be minimal. Try imagining a couple of horses there, how close would I have to get to match your depth blur. You would need a very wide angle lens to fit the horses in the shot and be close enough to reduce the DOF to that extent. With a narrower field of view you would need be substantially further away from the subject and have a super fast expensive lens (the f-stop would be smaller) to match your blur.

Of course depth blur can be used to give an epic feel, but only when the character is supposed to be tiny compared with the background.

I have a pretty good idea why you want to blur the background. To get the painterly feel you are after, to bring the focus onto the model (your lighting and central composition do that already) , to hide things in the background that you don't want people to see. I realise that you have your reasons, but I want to show you how it is going to be seen by professionals and audiences alike. They might think that it is a lack of your understanding guiding you rather than artistic reasons.

My final comment is on the textures on the ground. The grass seems out of proportion with the horses, a little small I think. It's best if the textures match as much as possible to really convince the audience of the scale of your model.

I hope you feel that I have helped you through this mentoring process. You have shown that you respond well to feedback and that you have an artistic flare, very hirable qualities.

Good Luck with the final hand in!


Sunday, August 9, 2009

Re: Yoli's Project Part 4

Hi Tessa

Thanks for your recent post. I was indeed beginning to confuse what were the important points to consider.

I have taken your advice and done away with my detailed skin texture, opting instead for a pale skin tone complete with SSS and subtle bump mapping. Additionally I have bitten the proverbial bullet and chosen a colour scheme with what I think is a more appropriate mixture of warm over cool. 

I did this by taking colours from a range of vintage Eastern advertising (having been introduced to in order to achieve the retro quality I had been aiming for.

I have since been working in comp to create more of a sense of contrast between the fore and background, as I feel the washed out look of the straight render is lacking in the focus you have been pointing me towards in your posts.

This is by no means the final look and I would appreciate any advice you could give me on improving it and achieving the soft quality of my 3D reference. As it stands I have the key and fill lights as separate passes and used an incidence shader as a fake rim light. In your last post you gave me some examples of the subtle colours of light sources which I would like to experiment here, in order to give the character a warmer glow.

Although I am now being pressed to render and comp in order to meet the deadline, I would still value your feedback on any aspect of the look, as I intend to develop the project post hand-in as my major showreel piece.
Thanks again


Friday, August 7, 2009

Extract on shadows

For everyone,

Some information on shadows, that I started writing for Holly, but think it would be of interest to everyone, not too in-depth but enough to get you started.

How you blur your shadow depends on the type of shadow, and the software. Both ways have their pro's and con's. [here's the science bit]

Shadow map shadows work by first of all producing a depth map texture (the shadow map itself) as if looking through the light then the software interprets by projecting this map back through the light to produce the shadow. Ordinarily this doesn't take into consideration transparent objects, but 'Deep shadows' do (I think this is called detailed shadows in Mental ray), sometimes it is an additional setting on the shadow map. Beware these textures have much bigger file sizes compared with ordinary shadow maps, although you can make the resolution smaller to compensate, so only use them if you need to see shadows with fine transparency detail such as when using fur.

The first pro is that they are quick, as a depth pass is a relatively simple calculation. Normally they are created first (sometimes in a pre-pass), temporarily stored, and then used in the render. You can also save out and re-use your maps. This is useful when you have a static scene with a moving camera, as you only have to do the shadow calculation once (sometimes know as once per job shadow maps). If you have a static set but a moving character, you might want to light the scene with one key light, and two shadow maps, one that is used once per job (and therefore is being reused) for the set, and a much smaller map for the character, which you will have to create for every rendered frame. In most software you can now specify a shadow camera, to use instead of the light, simply for the purpose of producing your shadow maps. This means that you can reduce the size of your shadow maps, and have more efficient renders, by focusing in on the thing that is casting the shadow, rather than the entire stage. Also you can adjust the angle/position of your shadow, without changing the lighting, a useful trick for faking lighting.

I prefer to use shadow maps, as it gives me the control I want with fast results. Some software producers have incorportated extra efficiencies, especially those that do not rely heavily on raytracing. Renderman shadow maps are written out as .tex files which is a type of mipmap. This is very efficient when rendering the frame as it will use the most appropriate texture size for the shot taking into consideration the distance of the objects from camera. It's too much to explain here but look it up if your interested.

The Con's are that they can be tricky to work with, especially if your talking big, complex maps. The software calculations can get things a tiny bit out, and self shadow objects that should be in full light. The bias setting is there to compensate for this small amount of understandable error, so you can put the projection of the shadow map back, or bring it forward to correct the results. Bias tends to be very small numbers, but is also normally dependent on the size of object in your scene so it might take a bit of experimenting to see the results. I have seen people brush off using shadow maps because it darkens their lighting, they don't realise they have self shadowing objects (or perhaps they trying to use one small map for too big an area) and that adjusting the bias will fix it. I believe can only make an informed decision when you understand some of the technical aspects behind lighting.

The accuracy of the shadow map is limited by its resolution, and to blur the map you can use the filter size setting (in maya) or the softness in Mental ray, although the softer you make your shadows the more samples you will need, otherwise you will quickly lose quality. Samples and Resolution sizes are normally set at numbers like... 2,4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096. They are to the power of two. It is way more efficient to use these numbers (I think for memory accessing reasons), so stick to the rule. If your not sure where to start when using these settings, start low, and work your way up until you see the quality/time balance that will work for your project. If your using a small shadow map, say 64 pixels square, on a PAL render of a character, the shadows might give the impression that they are soft. But watch out, you may only have the appearance that they are soft because the map is too small, there is a good chance that it will flicker frame by frame, due to there not being enough detail in the map, you are better off turning up the resolution to 512, and increasing the filter size/ softness. Another con is that many pieces of software do not yet have a shadow blur falloff inbuilt to work with shadow maps, so you might have to write one yourself or find a workaround if that is something you need. When it is implemented it does substantially slow down the render but it might be worth it to get the realism.

Raytracing is a type of shadow rendering where the path of individual light rays are caluculated from their source (the light) to their destination (the camera) [from the manual]. Professionals can see bad raytraced shadows a mile off, so if your going to use them, make sure you get your settings right. Light Radius values control the softness of the shadows, and is dependent upon the scene size. Shadow Rays controls the graininess of the edges of a softer shadow. Increasing the number of rays increases the quality and the render times "so set it to the lowest value that produces acceptable results" [from the manual]. Basically the more soft you make your shadow, the more rays you will need to clean up the graininess.

Only touch ray depth limit if you have lots of reflection/refractions of light going on, i.e. glass, behind glass and you need it to cast shadows, as in Nigel's project, but beware of render times. If you use the area light in mental ray, shadows blur and become lighter (falloff) as they increase in distance from the object, again at cost to you in time. Raytraced shadows are much slower because of the complex calculations, and because there is no way to get around doing them on a frame by frame basis, but it is relatively easy to get them set up and working.

[extract over. Hopefully having as much information as possible will give you the confidence to use shadows in a creative way]