Background Image / Picture Using Alpha Mask
Posted: Fri Sep 18, 2009 8:33 am
For Maximum control of your background image:
It is best to insert the background image into a photo editor for 2 advantages:
The key with Alpha Masks is to render them as large as possible but with the exact same aspect ratio as the original rendering, then to down-size the mask image to match the rendered image. For example, if the original rendering is made with an aspect ratio of 4:3(standard) or 16:9(widescreen), render the alpha mask with the same aspect ratio of 4:3 or 16:9. This is automatic if the "Fit to View Proportions" radio button is checked in the Resolution Section of the Render Tab in the Render Dialog Window.
The steps are very similar to the demonstration in the Tips and Tricks' Photomatch - Aligning a Rendering with the Original Image tutorial here.
It is best to insert the background image into a photo editor for 2 advantages:
- easily adjust the rendering output from Twilight so that color, resolution, and tone match the Background Image.
- adjust the background image so that color, resolution, and tone match the rendered image
The key with Alpha Masks is to render them as large as possible but with the exact same aspect ratio as the original rendering, then to down-size the mask image to match the rendered image. For example, if the original rendering is made with an aspect ratio of 4:3(standard) or 16:9(widescreen), render the alpha mask with the same aspect ratio of 4:3 or 16:9. This is automatic if the "Fit to View Proportions" radio button is checked in the Resolution Section of the Render Tab in the Render Dialog Window.
The steps are very similar to the demonstration in the Tips and Tricks' Photomatch - Aligning a Rendering with the Original Image tutorial here.
- open the Background Image, for example, "MyBackground.jpg" inside your photo editor of choice
- figure out the resolution of the "MyBackground" Image (look for a menu item "Image>size" in your image editor) It will give the size and resolution.
- render your model with similar resolution to maximize believability for the final composite image.
- save the final rendering in Twilight Render as "MyRender"
- in the image editor, stack the "MyRender" image as a new layer on top of the "MyBackground" image.
Now for the Alpha Mask - select your entire model, OR, be sure NOTHING in the model is selected.
- render alpha mask "MyRender_Mask" at TWICE the resolution of the MyRender image.
- in your photo editor open and resize the "MyRender_Mask" image to be exact same resolution of the "MyRender" image
- select the resized mask image and Edit>copy it to your computer's "clipboard"
- add an "Alpha Mask" channel to the "MyRender" layer, (now Alt-click on the mask in Adobe Photoshop to activate it) and paste the MyRender_Mask into that mask channel.
- now the image will have a high-quality/clean mask