CG Jam

Bokeh Blur node

Whats it for?? Bokeh blur Filter node.

how do I give my Background images that sweet blur with the little light ball effect? bokeh blur is your answer!

Whats it for?? bokeh blur filter.

Sooo, we are out of sequence slightly, simply because the we need to know this node in order to understand the Bokeh input node, which we will look at in the next episode.

so before we go into the node, we need to understand bokeh.

Blur, its just camera blur dude…

ok no its a bit more involved than that. Basically Bokeh is the blur you get from your camera but it also depends on your camera aperture size, the depth of field, F-stop and all that other camera goodness that photographers like to baffle everyone with. lets explain this quickly.

your aperture is the iris of your camera, how open it is is the F-stop, the smaller the F-stop the more open the aperture. like your eyes an open aperture lets in more light so the shutter can open and close really fast, which is great for portraits and for action shots.  a high F-stop means the aperture is more closed so less light can get in so the shutter takes more time to close, which is good for low light pictures and action.

the thing is, if you have a low f-stop, when the subject of your shot is in focus, the background gets blurred. perfect for portraits. as you increase the F-stop, the background becomes sharper.

ok good so far? no?

blur dude, its just camera blur…

one other feature of bokeh its that light sources, will blur in the shape of the camera shutter,  some cameras have more fins on the aperture than others and the fewer the fins the more polygonal the appearance of the light source.


so the node itself,

this node allows you to take a regular image and approximate this blur effect, details will be blurred out and light sources will take on this aperture shape.


the first input on the node is for your image, just plug in an image node and it will be blurred to the default settings. simple.

the second input is quite neat, it allows you to connect an image with an alpha that will define the shape of the light bokeh. this is achieved in a camera by placing a filter over the lens of your camera, like this image shot with a Nikon D50 by flikr user Michele M.F.


we can re create this effect by plugging a  white heart shaped png with an alpha background into  the bokeh socket.

the size value input obviously allows you to adjust the overall size of the blur, making it more or less blurred as needed in your shot. bit as its an input socket we can also add a texture to define the effect of the blur on the image,you do need to make sure the size checkbox at the top of the node is ticked for this to work though. So for example we could add a gradient texture so the blur would only affect the top of the image, or we could even use a mask to eliminate the blur effect around an element in your image that you would want to remain in focus.

the bounds input is however ideal for using the mask input as it will give a greater definition to the masked area, whereas the size would be a little bit more diffused.

bounding is pretty great for testing an area of your composition as you can use a box mask to just highlight a small part of the image to give you a  preview of the bokeh while you work on the image as the node does tend to hog the cpu quite heavily especially when you need to turn the size value up quite a bit! you can extend the bounds by ticking the check box, but really this does very little  so you might want to ignore that unless you find that one composition the it actually benefits!

so. thats bokeh blur, hopefully you learned something and in the next lesson we will be looking at an node that is specifically designed to work with the Bokeh input… its the Bokeh input!

have fun and post the results of your own experiments in the comments below!



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