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The 
Image Filter LOP lets you add effects like blur, chromatic aberration, or denoising to your images. All the Image Filter operators, available for the 
COP Image Filter List, are also supported by this node.
Technically, the node creates a HoudiniImageFilterList primitive on the stage that contains HoudiniImageFilter primitives. To make use of the filters in a render, you need a 
Karma Render Settings LOP. There you can find a convenient method for adding and configuring an Image Filter.
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On the render setting node’s Image Output ▸ Filters tab, go to the COP Image Filters List parameter.
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By default, there’s a single Filter Prim entry. When you click the
button, Houdini will add an Image Filter LOP to your network, connect it, and fill in the correct path to the HoudiniImageFilterprimitive, for example/Render/ImageFilter/imagefilter1. -
You can add multiple filter lists, rearrange their order, or turn them off temporarily.
User interface ¶
When you click the Image Filter LOP, you will see a parameter set that’s split into three areas:
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The top section controls, which AOVs will have the filters applied
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On the left part you can add, turn off, and rearrange the individual filters
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The right area contains the parameters of the currently selected filter
Working with filters ¶
The first thing you need is an object or scene to see an effect. A camera, on the other hand, isn’t mandatory for a preview, but recommended for evaluating the final look. To preview the filter(s) in the viewport, you must start a render from the first viewport menu. Open the dropdown menu and choose Karma CPU or Karma XPU.
Now you can apply one or more filters. Either 
-click the left part of the node’s UI, or just click the Add Filter button. Both methods open a dropdown menu with the available filters. As soon as you've added a filter, you can see its parameters and start to adjust the values. The interactive preview render (IPR) is also being updated with each change.
Additionally, all filters are listed in the Scene Graph Tree. There, you can also turn a filter on and off with the 
Active State button.
To delete a filter, -click its handle in the right area and choose Delete Filter.
Copernicus ¶
For every filter from the Image Filter LOP, you can find a counterpart in Copernicus. Add a COP Network to the stage, dive inside and open the tab menu. From the Filters menu, lay down a 
Chromatic Aberration COP. When you compare the parameter sets, you’ll see that they're absolutely identical. You can also use the COP node’s help cards if you need mire information about the parameters.
Limitations ¶
The Image Filter LOP takes a COP network and translates the parameters of the COP nodes to USD primitives. However, filter lists are not node networks that will re-cook if you change their wires. The node only translates parameters and makes them available in USD/Solaris. We therefore recommend leaving the internal COP filter lists untouched.
So basically all you can (or: should) do with the Image Filter LOP is to define filters and their order, fill in parameters, and render an image. A common application for filter lists is basic slap comp.
AOVs ¶
You can also apply filters to AOVs. By default, filters will only influence color AOVS. From Filtered AOVs dropdown menu, you can choose from various ready-to-use AOVs setups like All AOVs or List of AOVs. In the latter case you just enter a space-separated list of AOVs.
The Depth AOV, Albedo AOV, and Normal AOV parameters are required for filters with an appropriate input. For example, the Defocus filter has a depth input and will therefore need the appropriate AOV to work correctly. The Denoiser AI filter requires the albedo and N AOVs. This doesn’t mean that the filters will affect these AOVs. If you really want to apply a filter, for example, to the depth channel, you can choose Filtered AOVs ▸ List of AOVs and append the AOV. A typical list could then be C color depth.
If you don’t want to use the standard names for the three AOVs, you can define custom names as well.
Final rendering ¶
To use filter lists with the final render, you only have to start the render process as usual. Please make sure that:
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the image filter node(s) are added to the Image Output ▸ Filters ▸ Filter Prim parameter(s)
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you configure and turn on the relevant AOVs
When you start the render with one of the Render to … buttons on the 
USD Render ROP, the filter(s) will be baked to the final image.
Warning
With 3rd-party render delegates only work in husk!
Custom filters ¶
Copernicus already provides a long list of filters. However, more advanced users may have a need for custom filters. Please note that not all filters might be supported in custom HDAs.
The first step is to create a Houdini Digital Asset (HDA) from your Copernicus filter network. Depending on your network, you must configure the HDA’s inputs. For example, with a denoiser you’ll need the color image, but also albedo and normal AOVs. Please also mind the correct signatures - you can see them when you hover the mouse over the inputs of the filter node(s) in your network. For the 
Denoise AI COP, the signatures are RGBA (C) and RGB (albedo, normal).
When you configure the HDA, go to the Tab Submenu parameter and enter Filters/Post. This will add the custom filter to the Copernicus Filters ▸ Post tab menu.
Since the Image Filter LOP reads the entries from this menu, the filter will also appear in the node’s menu or when you click the button. Save the HDA to the standard location to make sure it’ll be loaded with every launch of Houdini.
