Render Layer Output
This option is only available if you have assigned parts and or models to a render layer. Select All Render Layers checkbox to enable layer ouputoutput. Select the gear icon to show the Render Layer Settings dialog and select the Alpha (Transparency) Mode for the layers.
The Render Layer alpha modes include:
- Straight Alpha - Unmatted - (Default) This alpha mode extends the color at the edges of Render Layers to the semitransparent pixels of anti-aliased edges. This avoids any black fringing when compositing the Render Layers in post-processing. This alpha type is the default, as it provides the best results in most situations.
- Premultiplied Alpha - Matted with Black - This alpha mode premultiplies the Render Layer image by blending or matting any semi-transparent pixels, due to anti-aliasing, with black. This can cause black fringing when compositing the Render Layers, if the image editing application does not support specifying the black matting color and adjusting for it. In Photoshop, the issue can be remedied by trying one of the matting options, found under Image > Matting.
- Aliased - Opaque Fringe - This alpha mode extends the color at the edges of Render Layers and creates fully opaque (aliased) edges. This avoids any transparent gaps between adjoining Render Layers when compositing the Render Layers in post-processing. Due to the negative visual consequences of aliased edges, this mode should only be used if gaps between Render Layers are a dealbreaker. Rendering at higher resolutions will make the aliasing less noticeable though.
The example below shows the Still Image rendering of two interlocking rings.
The outer (blue) and inner (white) rings were put on two separate Render Layers.
The examples below show the result for the different Alpha Modes when compositing the Render Layers on a solid green background color. Click the images to enlarge.
|Straight Alpha||Premultiplied Alpha||Aliased|
With "Straight Alpha - Unmatted" enabled, the Render Layer edges don't show fringing (black matting), and the green background color bleeds through the anti-aliased gap between the two Render Layers.
With "Premultiplied Alpha - Matted with Black" enabled, the Render Layer edges show black fringing, and the green background color bleeds through the anti-aliased gap between the two Render Layers.
With "Aliased - Opaque Fringe" enabled, the Render Layer edges show opaque and aliased fringing, and there is no gap between adjoining Render Layers, so that the green background color does not bleed through.
Enabling the render layers option will render all render layers created. To create a render layer go to the Project window, Scene tab. Go Properties, Render Layer to create a render layer. Select a part or group of parts and select the render layer you would like it to be on.
Render Layer example
The examples below show the different render layers of above scene.
|Render Layer "Body Panels"||Render Layer "Black Parts"||Render Layer "Flames"||Render Layer "Wheels"|
Render Layer "Tires"
Render Pass Output
Select All Render Passes checkbox or the checkbox next to the individual pass type to enable pass output. Doing so will render the selected pass(es), along with the original image format specified on the output tab. Select the PSD or PSD 32-bit option from the Format drop-down menu to enable the Add to PSD checkbox. This will compile all your passes into a single PSD file.
Render Passes are always saved as separate EXR files. This is done to allow maximum flexibility and quality in post-processing. Most modern image editing and compositing applications can work with EXR files.
Please note that when rendering to PSD (not 32-bit) with "Add to PSD" enabled, all Render Passes are embedded in a 8-bit PSD file. As a consequence, some information will be lost. If maximum flexibility is desired, PSD 32-bit should be used instead.
KeyShot supports 12 types of render pass output, including:
Compositing examples with Render Passes
Render Passes can be used in various ways during post-processing. Below are two basic examples of compositing workflows with Render Passes, using Photoshop to explain the concepts.
Some discrepancies may exist between the rendered still image and a composite using Render Passes. Furthermore, Render Passes do not capture some of the more complex material effects like translucency (Translucent material).
Reconstruct Beauty image from Passes
Passes can be used to reconstruct the rendered still image, commonly called the "beauty pass" in compositing workflows. Adding together the Lighting, Global Illumination, Caustics, Reflection and Refraction Passes allow to achieve the beauty image.
In Photoshop, adding is done by setting each pass layer's blending mode to "Linear Dodge (Add)".
|The pass layers with blending mode "Linear Dodge (Add)" in Photoshop||The composited result||The rendered still image (beauty pass) for reference|
Adjust Beauty image with Passes
The same passes from the workflow above can also be used to strengthen or weaken their effect on the beauty image.
In Photoshop, strengthening the effect of a pass is done by setting the pass layer's blending mode to "Linear Dodge (Add)". Weakening the effect is done by setting the blending mode to "Subtract". In both cases, the beauty image should be the base layer, positioned below the passes.
The example below shows the effect of adding the Reflection pass to the beauty image.
|The composited result: beauty + reflection||The rendered still image (beauty pass) for reference|
The example below shows the effect of subtracting the Global Illumination pass from the beauty image.
|The composited result: beauty - global illumination||The rendered still image (beauty pass) for reference|
Formats for Render Layers and Passes
Below is an overview of the image formats of Render Layers and Passes for the different output formats.
|Output Format||Render Layer Format||Render Pass Format|
|TIFF 32-bit||TIFF 32-bit|
|PSD||Last used format|
|PSD 32-bit||Last used format|