Mask operations come into effect when a selection mask is specified in the 2D plugin parameter panel. The mask supplied by trueSpace is rendered from either selected objects or the entire scene (background pixels are not selected). Due to this, the mask only covers the actual object being blurred and has sharp edges. Therefore, a standard blur filter will fail to blend the blur smoothly in with the background image. Mask operations allow you to increase the size of the mask and feather it's edge to blend the blur into the background.
Mask operators mostly affect the mask which trueSpace passes to Blur 'N' Feather. The simple expansion and feathering parameters form the core controls which soften the edge of the mask to to blend the blur into the original image. These, and possibly Normalize and Feather Out are all you need to control the mask under most circumstances.
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| Feather: 0 Fall: 4 Exp: 0 | Feather: 1 Fall: 4 Exp: 0 |
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| Feather: 1 Fall: 4 Exp: 1 | Feather: 2 Fall: 16 Exp: 1 |
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| Feather: 3 Fall: 4 Exp: 4 |
Colour Fill
The other main function of the Mask Operators is to modify the original image before blur. Four controls are used to achieve this, Mask Fill, BG Fill, Feather in BG and Replace BG.
Blur 'N' Feather segments the mask into three areas, 'original', 'modified' and 'background'. Fully selected pixels in the original mask are segmented to 'original'; pixels selected in the expanded/feathered mask, but not in 'original' are placed in 'modified'; and non-selected pixels are 'background'.
This first image shows a segmented mask, segments shown as original, modified and background.
Segmentation can be modified by Feather In BG. If selected, then only the expanded area of the mask is placed in 'modified'. The feathered section is assigned to 'background'. This boundary is show by the blue tick mark in the Edge Profile Preview.
Once segmented, the original image is copied and the 'modified' sections are filled with the Mask Fill colour and the 'background' sections with the BG Fill colour. The blur is performed on this image which is then blended back onto the original. By selecting Replace BG the 'background' segment can also be applied to the image. This can be useful if you're creating a blur for later composition. The main application for all this is when colour burning to ensure that the colour gradients fade correctly or creating glows around objects.
This blur used a Mask Fill: Red, BG Fill: Blue, Feather In BG: yes, Replace BG: no. Notice how the red fades to blue at the edges. (The mask segment image above was created with similar paramters except Feather In BG: no, Replace BG: yes)