compositing Improve your renders with photoshop and save time

[Jelmer]

Every CG artist uses adobe photoshop or a similar application regularly, but few improve "finished" renders from 3ds max or another 3d app in photoshop, maybe you should? why?



What's the point?

First of all you can save yourself a lot of time, of course you can change the material settings again, or shift that background image but your last render might have taken hours already, you don't want to wait that long again do you? Obviously this also makes editing in photoshop much more flexible, you can preview results within the blink of an eye and undo any changes you make.

Cheating is ok

Sometimes I've seen people call this "cheating" because they think it's not really 3d anymore but that's nonsense, CG and 3d is all about cheating . If you can make something appear "right" with a technique that wouldn't possibly exist in real life, do it, it's not a game where you should win by playing fair, all that matters is the end result, not how you achieve it (although stealing models from others is not recommended!)

Render elements!

Before opening up photoshop, there are a few things you can do within 3ds max to make life easier. A standard diffuse map already gives you some control, but if you add render elements/passes you can go a lot further. Here's a list of render elements we're using in this tutorial and their purpose:

• Diffuse (colour)
• Zdepth (for DoF)
• Alpha (background images mask)
• Shadow (shadow and lighting adjustments)
• Reflection (reflection adjustments, glow)

Although it might seem overkill it's not, we can do a lot of cool stuff combining the layers in photoshop, rendering time is ok as well, most of these elements are fairly quick to render, certainly compared to a standard render.

tip: If you're using final gather and/or Global Illumination, save the map and 'freeze' it so you don't need to re-calculate every pass!

Masks, alpha and Zdepth???

Are used a lot throughout this tutorial, so let's explain them first. A mask is used in photoshop to determine the opacity of a layer. So you start out with a layer and then apply the mask, which is basically another grayscale image, where a white pixel is 100% opacity and a black one 0% anything in between is obvious..

An alpha render shows the models in your scene as white, and anything else as black (the empty background for instance), obviously you can apply this as a mask for a custom background image. I was having some problems while rendering here, the areas which were supposed to be white turned out a dark gray colour, I had enabled expsure control for the normal render, and it was affecting the alpha render too, so don't forget to turn that off.

Finally we have the Zdepth map, which can be applied to add fog or haze as a mask again, because it has a value between pure white and black determined by the distance from the camera. This is also useful for DoF because it depends on distance too. Remember you can invert your maps and masks at any time in photoshop by pressing ctrl+I and adjust them in any way you like, be creative and experiment!


Zdepth + lens blur = Depth of Field


Image provided by forum member MrTom

Depth of field is very time consuming to render and can be difficult to control, using photoshop you can do it within a few seconds with a lot of control as well, here's how:

1. Render a zdepth pass along with your other passes or regular render. Make sure you set it up correctly, create a camera of the view you want to render (ctrl +c) and set the near and far range to properly render the zdepth, you should have values from white until black.

2. Open the standard image and zdepth image in photoshop, add a layer mask to the standard image, go to channels and paste the zdepth image in there.

3. Apply filter > blur > lens blur, be sure to play with the blur focal distance to adjust what's in focus and change the radius to control the amount of blurring (don't go too high, it won't look realistic..)

4. delete the layer mask again, to restore the original opacity, you're done.

glow (also known as bloom)

Can be really useful to increase the realism of lighting and reflections, it's another simple trick I use often. Be careful when using this though, you'll see it through windows when the sun actually shines through the window from that side, so if the window is on the shadow side of the building, it would be very unrealistic to add the effect, so it won't look right no matter how hard you try. First let's use it to add some bloom from light through a window:



1. render an alpha pass, fill a layer with white and apply the alpha render as a layer mask, you might need to invert it.



2. Apply gaussian blur to the mask and see what happens, finally play with the opacity, levels and brightness and contrast of the mask to get the intented result.

Glow is also visible on car paint shaders often. Most of the time, if you have white bright reflections (eg. a studio lighting environment) copy the reflection layer, adjust levels for more contrast between black and white and use that as a layer mask on a white layer. Finally apply Gaussian blur to get the blurry glow effect going.

Haze in the distance

This works especially well for landscape type renders, in combination with a zdepth map to add some fog. Often I see unrealistic renders because the atmosphere, mainly the amount of saturation, and likeness to the sky colour is the same at any distance from the viewer/camera. In reality objects blend into the sky eventually, or you could say the "have" the same colour. This is because particles in the air between the viewer and object affect the object's colour, obviously if you increase distance so does the amount of particles. Here's a photograph to illustrate the idea:



Now let's apply the idea with photoshop and a zdepth layer.

1. Render a zdepth pass/render element within 3ds max, and open it up in photoshop with your standard render.

Tip: Add a background image first so you can determine the right colour of the sky and haze. Keep on reading to learn an easy way to do just that.

2. Create a new layer and fill it with the main sky colour. Apply a layer mask, go into the channels tab and paste the zdepth layer, invert it with ctrl+i. You can adjust the amount of haze by playing with image > adjustments > brightness - contrast and levels. that's all:



Change the atmosphere.

The colours of your artwork have a great influence on the feeling and emotions your work evokes. Some colours are just more appropriate for a certain story or idea. There are lots of possibilities to adjust your colours, first of all it's important to select what you want to edit, try select colour range and the magic wand. Then you need to edit the colours, if you want to do that in a non destructible way, adjustment layers are very useful, you have more influence on the result since you can play with opacity and layer blending modes.

Adding and matching a background

This is already quite easy to do in max (plane with image applied) but in photoshop it's far more flexible and more accurate using an alpha map, which we use to mask the area where no model was rendered in max. here's the workflow:

1. Render an alpha pass of your standard render and open it in photoshop.

2. Find a suitable background image, when searching for images make sure you think about perspective, I've seen many images that look too fake because the perspective doesn't match, if it's not perfect you can adjust it with photoshop though. Also, don't forget about the right scale, if it's of it will look just as bad.

3. Press ctrl+t and move the control points to adjust the background image and match the perspective. Sometimes you also need to change the colour a bit, use image > adjustments > hue/saturation or variations and play with the settings until they match your render, or the other way around.

4. Apply the alpha render as a mask on the background image layer and adjust the position of the background image to your liking. That's all, you can save yourself quite some time and adjust the position and look of your background easily with this technique.

Tips: Rotate and move the background image to match the render's horizon line, adjust the colours to match the lighting of the render. Also be careful with light direction, if the shadows of your background go the other way it will look really fake of course.



The Photo look

Photographs are never perfect, 3d renders are just that all too often but of course you can add some imperfections with photoshop! First of all photos always have some noise, especially when you increase the ISO speed (usually done in lower light conditions), or if you have a really cheap compact camera, while cameras are designed to limit this effect, you should add some to your 3d renders by simply applying some filter > noise > add noise.

Of course all the other effects discussed in this article are also found in photography, especially Depth of Field, if you have a camera (Dslr preferably) just play around with it and see what happens when you change the settings, then apply them to your 3d renders.


I hope you enjoyed this article, and above all found it useful, the best advice I can give you is to keep experimenting, things don't work out perfectly the first time, I had some trouble with achieving the wanted effect in this tutorial as well, be creative and try something different!

[fsd]

Thanks for posting Jelmer. It was interesting.

[elpvn]

Great works, Jel !
Thanks for sharing

[fahid_2003]

Thanks for sharing..........Jelmer........

nice tut

[fadl4]

Thank you Dear...

[darth]

Nice tips... thanks for sharing

[clarajean]

Cool!!! will apply it in my projects. thanks for sharing

[MagnetMike]

I have no trouble generating the zdepth image but for some reason the edges are VERY jagged. I have tried turning on a filter but it doesnt allow me to?! When I create the 'fake' DOF in PS you can see the rough masking from the zdepth image? Any idea how to fix this? Thanks!

[MagnetMike]

sorry..figured out the answer to my last post...thanks anyway.

[killoskate]

nice...i will give this a try.