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manual/composite_nodes/types/converter/set_alpha.rst
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| Set Alpha Node | |||||
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| .. figure:: /images/Tutorials-NTR-ComSetAlpha.jpg | |||||
| Set Alpha node | |||||
| This node adds an alpha channel to a picture. Some image formats, such as JPEG, | |||||
| do not support an alpha channel. In order to overlay a JPEG image on top of a background, | |||||
| you must add an alpha channel to it using this node. | |||||
| The *Image* input socket is optional. If an input image is not supplied, | |||||
| the base color shown in the swatch will be used. To change the color, :kbd:`LMB` click | |||||
| the swatch and use the color-picker control to choose or specify a color you want. | |||||
| The amount of *Alpha* (1.00 being totally opaque and 0.00 being totally transparent) | |||||
| can be set for the whole picture using the input field. Additionally, | |||||
| the Alpha factor can be set by feeding its socket. | |||||
| .. note:: | |||||
| This is not, and is not intended to be, | |||||
| a general-purpose solution to the problem of compositing an image that doesn't contain Alpha information. | |||||
| You might wish to use "Chroma Keying" or "Difference Keying" (as discussed elsewhere) if you can. | |||||
| This node is most often used (with a suitable input being provided by means of the socket) | |||||
| in those troublesome cases when you *can't,* for some reason, use those techniques directly. | |||||
| Using SetAlpha to Fade to Black | |||||
| =============================== | |||||
| To transition the audience from one scene or shot to another, | |||||
| a common technique is to "fade to black". As its name implies, | |||||
| the scene fades to a black screen. You can also "fade to white' or whatever color you wish, | |||||
| but black is a good neutral color that is easy on the eyes and intellectually "resets" the | |||||
| viewer's mind. The node map below shows how to do this using the Set Alpha node. | |||||
| .. figure:: /images/Manual-Compositing-SetAlpha_fadetoblack.jpg | |||||
| Fade To Black | |||||
| In the example above, the alpha channel of the swirl image is ignored. | |||||
| Instead, a :doc:`time node </composite_nodes/types/input#time_node>` | |||||
| introduces a factor from 0.00 to 1.00 over 60 frames, or about 2 seconds, | |||||
| to the Set Alpha node. Note that the time curve is exponentially-shaped, | |||||
| so that the overall blackness will fade in slowly and then accelerate toward the end. | |||||
| The Set Alpha node does not need an input image; instead the flat (shadeless) black color is used. | |||||
| The Set Alpha Node uses the input factor and color to create a black image that has an alpha | |||||
| set which goes from 0.00 to 1.00 over 60 frames, or completely transparent to completely opaque. | |||||
| Think of alpha as a multiplier for how vivid you can see that pixel. | |||||
| These two images are combined by our trusty AlphaOver node completely (a *Fac* tor of 1.00) | |||||
| to produce the composite image. The SetAlpha node will thus, depending on the frame being rendered, | |||||
| produce a black image that has some degree of transparency. | |||||
| Set up and Animate, and you have an image sequence that fades to black over a 2-second period. | |||||
| .. note:: No Scene information used | |||||
| This example node map does not use the RenderLayer. | |||||
| To produce this 2 second animation, no blender scene information was used. | |||||
| This is an example of using Blender's powerful compositing abilities | |||||
| separate from its modeling and animation capabilities. | |||||
| (A Render Layer could be substituted for the Image layer, | |||||
| and the "fade-network" effect will still produce the same effect) | |||||
| Using SetAlpha to Fade In a Title | |||||
| ================================= | |||||
| To introduce your animation, | |||||
| you will want to present the title of your animation over a background. | |||||
| You can have the title fly in, or fade it in. To fade it in, | |||||
| use the SetAlpha node with the Time node as shown below. | |||||
| .. figure:: /images/Manual-Compositing-SetAlpha_FadeInTitle.jpg | |||||
| Using Set Alpha to Fade in a Title | |||||
| In the above example, a Time curve provides the Alpha value to the input socket. | |||||
| The current RenderLayer, which has the title in view, provides the image. As before, | |||||
| the trusty AlphaOver node mixes (using the alpha values) | |||||
| the background swirl and the alphaed title to produce the composite image. | |||||
| Notice the *ConvertPre* -Multiply button is NOT enabled; this produces a composite | |||||
| where the title lets the background image show through where even the background image is | |||||
| transparent, allowing you to layer images on top of one another. | |||||
| Using SetAlpha to Colorize a BW Image | |||||
| ===================================== | |||||
| .. figure:: /images/Manual-Compositing-SetAlpha_Colorize.jpg | |||||
| Using Set Alpha to Colorize an Image | |||||
| In the example above, notice how the blue tinge of the render input colors the swirl. | |||||
| You can use the Set Alpha node's color swatch with this kind of node map to add a consistent color to a BW image. | |||||
| In the example map to the right, | |||||
| use the *Alpha* value of the SetAlpha node to give a desired degree of colorization. | |||||
| Thread the input image and the Set Alpha node into an AlphaOver node to colorize any black and | |||||
| white image in this manner. Note the *ConvertPre* -Multiply button is enabled, | |||||
| which tells the AlphaOver node not to multiply the alpha values of the two images together. | |||||
| No newline at end of file | |||||