This short tutorial has been written for 3ds max and vray users, but most probably you can easily “translate” the workflow in your favorite 3d software programs.

Everybody knows that when using indirect illumination (GI), the color of the materials in a scene affects other objects as well, due to the light that “borrows” color information from a surface after having “bounced” from it.
Although it is normal and happens in real life as well, sometimes the bounced light is affecting the scene too much and it doesn’t look right.
The most common situations when this happens is when you have a wooden floor and the color ceiling and the walls becomes too red/orange (like in the example bellow).

If you use “linear workflow” that is less likely to happen, but if the deadline is knocking on your door, you need a quick way to adjust it and not lose time trying to find ways to do it directly from the render ( and completely change your workflow).

Here is a quick solution that can prove useful in situations when time is a major factor:
Make the material of the wall and ceiling a vraymtl wrapper, keeping the base material as it was.
Under “alpha contribution” type “-1”, hit render and save the resulting rendering as a tiff with alpha channel.

Open the rendering in photoshop, click on “select”, choose “load selection” and choose “alpha 1”. Now invert the selection, and you will end up with the selection of the walls and ceiling (which are the elements that are affected too much by the light bounced from the wooden floor).

With the selection active, use the hue/saturation slider from “image”, “adjustments” drop down menu until you obtain a desirable result. You can also use brightness and contrasts or level adjustments if you feel necessary.

Bellow is the result I achieved following the steps shown above.

Although this tutorial is aimed particularly at de-saturating colors on some elements of the scene, the same method can be applied in order to color correction adjustments on any particular materials you need, by making separate alpha channels for those specific materials and adjust the color and saturation from photoshop.

Brief introduction
Depth of field can prove to be a very effective way to add a “special” touch to an architectural rendering, or simply to focus the composition on a specific element.

Technically speaking, there are several possibilities to add dof to an image.
One way to do this is to add it from the vray camera rollout (if you are using vray), but keep in mind that the rendering times can go through the roof, so unless you have a render farm you may not want to consider this option.

Another way to achieve this type of effect is by adding it from the “effects” tab in 3d max. Even if this is way faster (being just a post-processing effect) I always feel the need to have more control over it regardless of the camera position or direction.

Rendering a separate zdepth pass
So here’s the way I do it.
Under “Render Elements” click “add” and choose “vrayZdepth” (if you not with vray you can chose Zdepth instead of vray z depth, or the equivalent of your rendering software).

After hitting “render” you will notice that you end up with 2 rendered images, the main image and another one in gray scale. If you look closer at the gray scale rendering you realize that objects that are close to the camera are light gray, and they get darker as the distance between them and the camera increases.

Post processing the zdepth pass
Open both renderings in photoshop.
Select the main rendering and duplicate the “background” layer. With the newly created layer active, click on “layer” drop down menu (at the top, between “select” and “image”), click “layer mask” and select “reveal all”.

Select the grayscale rendering and invert it (image>adjustments>invert). Now using the “rectangular marquee tool” drag a selection over the entire image than press “ctrl+c” in order to copy it to the clipboard.

Select the first image again and click the “channels” tab. Activate the previously created mask (under RGB, red, green and blue channels) and press “ctrl+v” in order to copy the zdepth mask.

Click the “layers” tab and select “background copy” layer to make sure you have the layer itself activated (and not the mask).

Go to “filters” and apply a lens blur filter.
As you will notice, thanks to the zdepth mask, the lens blur is affecting more the objects that are further away, and has less effect to the ones closer to the camera.

The big advantage of using this method is that you can control the depth of field anyway you want, simply by editing (painting) the zdepth rendered pass.
Here are 2 examples that show the flexibility of this method.
Click the renderings to view higher res ones:

Photomontage renderings, if done right, can be a lot more appealing and realistic than standard architectural renderings.
The reason why this happens is that a real environment with dust, dirt, scratches and imperfections, by definition looks better than a computer generated one.

Furthermore, creating the entire scene in 3d can prove to be very time consuming, and if you are working in the architectural visualization business you know that deadlines are usually very tight and you can not afford to lose more time working on the environment than on the building.

Having said this, let’s start with the tutorial. Usually photomontages are used for exterior renderings, but in order to keep this tutorial as simple as it can be, I have chosen an interior environment.

Taking the photo
The most important thing when taking a photo that you will later use for camera match is to take as many accurate measurements as possible (you will need at least 5 reference points). Take a look at the photo below (click on it to view a higher resolution image)

As you can see, the dimensions are noted on all 3 axis (horizontal, longitudinal and vertical).

The next step is to bring the photo into 3ds max. Click on “views”, “viewport background”, or just click “alt+b” (shortcut for 3ds max 9).
Under background source, chose the image you need and select “match bitmap” under aspect ratio.

Tick “display background” and select “active only” (with the perspective viewport active).
Click the image to view a higher resolution one

Now it’s time to model some basic geometry that we will later match with the photo.
Make sure that under “units setup” in the preferences drop down menu the units are set to the same ones noted when you made the measurements (in this case, centimeters).

You don’t need to model anything fancy… just a set of planes with the same dimensions as some elements in your scene. You need a 90.5×45 cm plane for the table top, a 20×20.2 plane for the vase and another plane placed at a distance of 4.6 centimeters behind the table top for the wall.

At this point it’s time to match the points of our geometry with the ones from the photo.
With the perspective viewport activated go to “create”, “helpers”, “camera match”, “cam point”. With the snap toggle on, start creating cam points at the corners of the table top plane, and at the top corners of the plane for the vase.
Click the image to view a higher resolution one

Go to the “utilities tab” and click “camera match”. You will see the list with all the cam points you have created in the previous step.

Select cam point 01, and click “assign position”. Now click the top left corner of the table top on the background image. By doing this you will tell the software that the cam point 01 needs to be placed at the position you have indicated.
Repeat this step for all the cam points.
Click the image to view a higher resolution one

After having done this, click on “create camera”. If everything has been done correctly, this step will automatically generate a camera that matches the view of the photo.
If you place a 3d model on the 90.5×45 plane in your scene, it will appear to be on the table top when rendered.
Click the image to view a higher resolution one

General camera match advices
As I said at the beginning of the tutorial, camera match can help you create a photorealistic rendering in a shorter amount of time. However, it has a downside too; unlike a standard 3d rendering, you can not change the angle later, so it is better to take several photos of the environment and explain to the client that he needs to decide upon a view and he can not change his mind later.

Taking dimensions for an exterior photomontage can proof to be more difficult than in the example shown in this tutorial. Therefore it is good idea to have objects with standard dimensions in your photos (like lighting posts, traffic signs, etc.)

Bellow are 2 examples of photomontage renderings that I have done using this techniques (click on the images to view high resolution renderings).

Bellow is a small list of things that I consider important when doing architectural visualization (or any other subject, as long as it is supposed to be a photorealistic rendering), and from what I see in the image galeries, a lot of people don’t seem to care about.

1)    Use chamfered edges, especially in close-ups
In real life there’s no such thing as “razor sharp” edges. Take a look at the objects around you and notice that every edge is more or less rounded. Although in the cad files provided by the architects you will never see this, keep it in mind when building the 3d model. Bellow are a few images that illustrate better what I’m trying to say.

(click on an image to view a higher resolution one)



Chamfered edges not only will make your 3d models look more real, but also may “catch” specular highlights which will give more depth to the rendering.

2)    Don’t use 100% black or 100% white colors.
The explanation for this is very simple. To “show” an object’s volume you need to have highlighted areas, shaded areas and mid tones. This is one of the first things that you learn at art school. If a material that is assigned to a 3d model has a 100% black color in the diffuse channel, there will be no visible difference between the mid tones and the shaded areas and it will make your model look flat. Same thing goes for 100% white objects, only this time there will be no significant difference between light areas and mid tones.

3)    Blur parameter from 1 to 0.1
By default, the blur parameter in the bitmap’s “coordinates” rollout is set to 1. This causes the textures to look blurred, especially if they are looked at from an angle. By setting this parameter to 0.1, will make the texture look sharper and therefore more real (it will also increase the rendering times though…)

4)    Always use area shadows.
If you are doing an exterior rendering, you need to control the sharpness of the shadow, depending on the time of the day. In the morning the shadow is very soft, and it gets sharper and sharper until mid-day; after that moment, it softens again until night.
Even at mid-day the shadow is not 100% sharp though so you still need to use area shadow, just adjust the parameter to make it less soft. The photo below has been taken at mid day; take a look at it to see how crisp/soft is the shadow.

Same goes for artificial lighting. Some fixtures cast a subtle shadow, while others (like spotlights) cast a sharper one, but again you should always use area shadows and adjust the parameters accordingly.

Hope these were helpful; feel free to add to the list if you wish.