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Tutorials: Basic Rendering & Advanced Rendering

Concepts

Flame Algorithm - what its doing

The Flame algorithm begins with a pool of totally random points in space.
The following iterative calcuation is done quality X width X height times:

A random point is selected from that pool.
One of the fractal’s Transforms is randomly selected. (Transform weight determines the probability that a particular Transform is selected.)
A new point location is calculated for the point by transforming the points location by:

1. Applying the pre-transformation operation to the point
2. Using the transform equation, a new point location is calculated.
3. (Optional) Applies the post-transformation operation to the point.

If the new point location falls inside the fractal viewport (visible part of the fractal), a Hit is recorded on the fractal Histogram. This Histogram is largest piece of render state and can be saved to disk. This is the time consuming part of the render process and can literally end up being done a million times or more.

Density Estimation is a step that tries to remove noise from the final rendered image, by blending the low density areas of the histogram.

Post processing is the final step that converts the histogram to the final image.

The final image quality is dependent on the Quality setting. Higher quality means more iterations. In the old days, you would have to repeat the entire render to get a higher quality image. Guessing the best Quality setting was an art.

Render Tiling

The render process consumes a lot of memory to hold the Histogram and the final image. If there is insufficient memory available to render the specified image size, the image is broken into smaller tiles that are rendered one at a time. These tile images are then combined to create the final image.
The number of tiles required depends on the amount of free memory available on the Mac at the start of the render and the size of the final image.

Render to Completion - Normal operation

If you start a render (and do not choose to Save the Render State) and let it run to completion, no render state is saved. You can not add more Quality to the render later (except by running the entire render again).

Pause and Resume Render

If you start a render (and do not choose to Save the Render State) you can click the Pause Render button to stop the render and have the render state saved to disk.

You can quit the application and at some time in the future, restart the application and open the saved RenderState file. Clicking on the Resume Render button of the Render State panel will resume the render.
You can let it run to completion or interrupt the render by pressing Pause Render again.

Complete versus Incomplete Render State

If you have not chosen to Save the Render State (a checkbox on the Render to File panel, where you start the render from) and your image requires more than one Tile to render, you do not have the Complete render state. (This allows you to resume the render, but does not allow you to add more Quality to the render). As an exception, if only one tile is needed for the render, you do have Complete render state.

If you have chosen to Save the Render State (a checkbox on the Render to File panel, where you start the render from), you do have Complete render state, and can both resume the render and add more Quality to the render.

Save Render State for all Tiles

If you have chosen to Save the Render State (a checkbox on the Render to File panel, where you start the render from), the render state for all tiles is saved to disk. You can pause the render and resume it, and can add more Quality to the render later.

Recharge Quality - Add more Quality

If you have Complete render state saved to disk, you may add more quality to the render.

For example, lets say you chose to render a file at 300 quality and chose to Save the Render state. A Render State window will pop up and show the render progress. You wait for the render to complete and inspect the rendered image. If the image quality is not good enough, you can add more Quality and resume the render again.

So lets say you change the quality to 600, the render will resume and 300 more quality will be added to the render.

Post Processing

If you have the Complete render state and the render is finished, you can change the post processing related fractal parameters and post-process again. Since you have the complete fractal render state, post-processing is quick. Most frequently, you would adjust Gamma Threshold and turn on/off the Density Estimation step.

Post-Processing Related Parameters

Gamma	Effects conversion from histogram units to actual color pixel values. Logarithmically scales hits to luminosity. Normal range 2 to 4.
Gamma Threshold	Linearized hit-to-luminosity gamma conversion threshold. Usually a very small positive fraction. Normal range 0. to 0.02
Brightness	Effects overall image brightness.
Vibrancy	Effects color saturation. Small values desaturate the image colors. Normal range 0 to 1
Density Estimation	Turns on/off Density Estimation portion of Flame algorithm.

Where is the Saved Render State stored

There is a new file type (whose file ending is .flrs) that holds the render state. Render state can be large, usuallly about 5X the size of the final image.

Viewing the Histogram(s)

Click the Show Histogram button to open the Histogram window. If there are multiple tiles, first select the Tile to view, then click the button.