Generating Large Images

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Generating Large Images

To generate large images you use the Generate Scaled Image command on the Tools menu of the Fractal Window. The Generate Scaled Image command will scale the fractal in the Fractal Window and generate the scaled image.

When you execute the command, the Save Image dialog is displayed so you can select the image type, and specify the name and folder for the image file. Next, the Generate Scaled Image dialog is displayed so you can select a Scale Factor. The width and height of the current fractal are multiplied by the Scale Factor to determine the size of the resulting image. To generate the image, the fractal is divided into an NxN grid, where N is the Scale Factor. Each grid cell is used to generate a new image as large as the original fractal, and these are combined into a single scaled image. The Shut Down Computer option can be checked to shut down the computer when the command completes.

The Ok button initiates the image generation.

The Cancel button cancels the request and closes the dialog.

The Help button opens the documentation in your browser to this page.

All the properties (e.g., Anti-Aliasing) used to produce the scaled image are taken from those in effect when the fractal was generated; i.e., any properties you may have changed since you generated the fractal are not used. You should generate a fractal that is exactly what you want but for size, and then use the Generate Scaled Image command to generate the larger image.

The time required to generate the scaled image depends on the original fractal and the Scale Factor you choose on the Generate Scaled Image dialog. At a minimum, the time will be NxN times longer than that required to generate the original fractal. For example, if the original fractal takes 2 minutes to produce and you select Scale Factor of 4, the scaled image will need to generate 16 images to form the scaled image and you should plan to wait at least 32 minutes (2 x 4 x 4) for the process to complete but it could be far more (see the discussion of Orbital Fractals below)!

There are a few caveats that you should be aware of.

Mandelbrot Fractals

Mandelbrot Fractals lend themselves well to the strategy used here. The estimate given above is usually a good one. When generating a scaled image from a Mandelbrot fractal, you can use a small fractal with a large scale factor or a large fractal with a small scale factor and the time to produce either image should be about the same. For example, you could generate a 4800x4800 image from a 1200x1200 image using a scale factor of 4, or from a 600x600 image using a scale factor of 8. The time required to produce the 2 images should be about the same.

Orbital Fractals

Orbital Fractals are problematic due to the way they are generated and the estimate given above will need to be increased when generating Orbital fractals. In contrast to Mandelbrot Fractals where we generate an orbit for each pixel in the viewing window to produce a picture, Orbital fractals generate a single orbit and we keep track of all the points we visit during the orbit. When you zoom into an Orbital fractal, you need to increase the size of the orbit in order to maintain the same level of density as in the original fractal. In fact, when scaling Orbital fractals, the Generate Scaled Image command increases the size of the orbit by a factor of NxN for each of the individual grid cell images, which requires that we multiply the above estimate by this factor as well.

For example, if the original fractal takes 2 minutes to produce and you select Scale Factor of 4, the scaled image will need to generate 16 images to form the scaled image and you should plan to wait at least 512 minutes (2 x 4 x 4 x 4 x 4) for the process to complete.

You should try to use as low a scale factor as possible (6 or less) to minimize the impact on the fractal generation time.

L-System Fractals

L-System Fractals are handled differently. Since L-System fractals do not maintain sample data as do Mandelbrot and Orbital fractals, we can simply expand the output image used to display the L-System fractal and draw directly into the expanded image, which is exactly what we do.

Textures

When you use textures in a scaled image, you need to make sure the resolution of your texture is high enough to support the scale factor you choose. As each grid cell is generated, it is magnified by the Scale Factor and and low resolution texture could be magnified to the point where you can distinguish the individual pixels in the texture which reduces the quality of the resulting image.

Memory

To generate the scaled image, the application requires at least as much memory as was required to generate the original fractal plus enough memory to hold the final scaled image. On low memory machines, you may need to free the memory used to hold the sample data for the original fractal before you execute the Generate Scaled Image command. To do this use the Clear Sample Data command on the Tools menu of the Fractal Window.

 

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