When you work in a production in the real world, you face 2 major problems:
1-You never have as much time as you want and,
2- The customer is always makes trouble.
For example, let's say you have to make a car render for your customer, and you've done a great deal of work. When the customer looks at the result, they may not like the color of the car, the reflections may look weak or the shadows may be more specific. They may dislike the ground or background, or say something else. All of these are nightmarish comments for a 3D artist and means to make changes and re-render. Time is lost.
The solution is to render the components separately (color, diffuse, specular, reflection, shadow, SSS) and combine them all into a compositing software. This is called Render Pass for these different render components and Multi-pass compositing (or simply Compositing) for processing these components in compositing software.
With this method, the result can be achieve quickly. If the customer changes the color, the layer (pass) that is the only color can be changed and the result can be seen immediately. You can win both times, and instantly show the changes while your customer is with you.
The render passes used for compositing are also used to show your render output more realistically. Compositing is a profession. And it has its own rules and tricks. This is why we recommend you to develop yourself in the field of compositing, not just with 3D creation. In this regard, you can find many paid or free courses on the web.
The following diagram shows a classic compositing style of work.
Important Note: Always use the Octane Render section to save the Render Pass file. Do nothing about the render pass section in Cinema 4D.
Important Note 2: If you see jagged edges in your multi-pass, make "Premultiply Alpha" active or inactive from Camera Imager settings. Also check your Passes in the Live Viewer before you get the Final Render.
Important Note 3: When rendering multi-pass, be sure that your bit depth depth is always 16-32 bits. You can even forget 8-bit and don't come back for it.
TONEMAP VS. LINEAR
In Octane, Live Viewer or Picture Viewer render is default Tonemapped. Each response curve you choose from the Camera Imager or post effcets is reflected in the final render. This is the default render behavior unless you select Linear. However, when you choose Linear Workflow, the ToneMap and Linear options have a different meaning. If you'll get a Render Pass, your first choice should be Linear (do not forget 16-32 Bit depth). Leave "Image color profile" and "Tonemap Type" as Linear. Render Pass output means that you will be compositing. In this case you will see the raw output of the Linear in the compositing software. Comp everything accordingly. But if you render out of Tonemap type, and your passes are in Linear, then you'll have problems with compositing. This is true for all render pass types in Octane (and all other renderers). In this case, you may have to do a lot of comp operations to get the same result in LV. If the image in LV is the final result for you, you no longer need to enter the linear adventure.
In the following picture you can see the rendered Z-depth passes for both Tonemaped and Linear. The Tonemaped image is what you see in the Live Viewer. On the other hand, Linear is almost white. This is because the data range is too large. This makes it possible to work comfortably in a wide range of colors. However, if you open this linear image render in After Effects and extract it, you will get the correct image. And you can continue comp operations. We explained the linear working logic under the "Linear Workflow" section.
OctaneRender’s Render Passes allow users to segregate the different aspects of the scene, respectively rendering each aspect across multiple images. This is particularly useful in fine-tuning projects, compositing, and creating remarkably detailed and photorealistic images. Render passes allow a rendered frame to be further broken down beyond the capabilities of Render Layers. Render Passes vary among render engines but typically they allow an image to be separated into its fundamental visual components such as diffuse, ambient, specular, etc.
Now let's take a look at the Render Passes main settings:
If you enable it, you will see both Render Passes in real time in Live Viewer and also enable export option in Picture Viewer. It will be very convenient for you to check the passes at the Live Viewer before you get the final render. In the final render, the options you select will be exported.
Here you specify where you will save the Passes.
You can put a seperator at the end of the file. Sometimes the pass names are mixed with the main file name. For example, you can put a underscore (_) sign here to separate the file name and the pass name.
You can select the image format of the passes from here. The format you choose according to Tonemap or Linear workflow is also important. For example, the most logical choice for the linear workflow is the EXR format. You can also choose 8 bit formats such as Jpeg, Png or Targa.
You can adjust the bit depth from here and for the final compositing you have to choose according to the quality you need. EXR 32-bit is the maximum quality, but the file sizes will be quite large. You also need a good computer configuration to do compositing with 32 bit-depth. We recommend that you determine your needs first.
It will save the selected render passes into a single layer file. Think like a Photoshop file. If you open this file in any compositing software, you can see your Passes layer by layer.
It is an option that appears when you disable the Multilayer. In this option, all of your selected Passes are saved with their folder names. It is useful if you render a lot of passes.
image color profile (click here for lInear Workflow)
There are 2 options: sRGB and Linear. sRGB is the color space you are currently working with. It can be 8 or 16 bits. Linear color space is for the maximum quality and accurate compositing. Here, too, it becomes important how and where the final output will be shown or play. If you are only working on 3D creation for a motion picture (or some production process), then this decision is made by Director of Photography, Technical Director and Creative Director. And most likely they are going to require a Linear output. If your goal is to play videos on channels such as youtube or vimeo, it is logical to choose sRGB rather than Linear.
The previous description also applies to this option. Maximum quality and control are always at Linear outputs. In addition, the most suitable workflow for color grading is Linear Workflow. However, Tonemapped outputs are also quite good and working on them are also very easy. Choose wisely depending on your purpose.