######################################################## Lee Skinner wrote: ------------------
... most of the area outside the lake will have the same color.
Lee, Thanks for the clarification of this detail of the Logmap problem caused by not adjusting or turning it off when zooming out of images that have Logmap set to non-zero values. What you say makes sense. For those of us who enjoy calculating fractals by creating variations on images created by others this has been a very useful discussion. ----------------------------------------------------------- Below is an excerpt from pages 84 & 85 of V20.0 Fractint's FRACTINT.DOC documentation about the use of Logmap. (Create FRACTINT.DOC with the command: FRACTINT.EXE makedoc typed at a command prompt while your default directory is the Fractint directory. FRACTINT.DOC is actually an ASCII text file, so you can rename it to FRACTINT.WRI to get the MS Write text editor to open it -- which is faster than letting MS Word open a .DOC file.) -------------------------------------------------------- Especially note this info about Logmap: "This results in spectacularly different images..." Also note the short, example given in the table towards the end of the excerpt about how a single cycle of the color map colors is redistributed over the entire range of a fractal's iteration values. This example is for the Ranges= parameter, but a remapping of the colors in the color map of a similar nature is done by setting a non-zero Logmap parameter on the <X> page in Fractint. Logmap calculates which iteration value to assign to each color for you, whereas Ranges= allows you to specify the distribution of the color map colors yourself. -------------------------------------------------------------------------- " Fractint Version 20.0 Page 84 . . . 3.7 Logarithmic Palettes and Color Ranges By default, Fractint maps iterations to colors 1:1. I.e. if the calculation for a fractal "escapes" (exceeds the bailout value) after N iterations, the pixel is colored as color number N. If N is greater than the number of colors available, it wraps around. So, if you are using a 16-color video mode, and you are using the default maximum iteration count of 150, your image will run through the 16-color palette 150/16 = 9.375 times. When you use Logarithmic palettes, the entire range of iteration values is compressed to map to one span of the color range. This results in spectacularly different images if you are using a high iteration limit and are zooming in on an area near a "lakelet". When using a compressed palette in a 256 color mode, we suggest changing your colors from the usual defaults. The last few colors in the default IBM VGA color map are black. This results in points nearest the "lake" smearing into a single dark band, with little contrast from the blue (by default) lake. Fractint has a number of types of compressed palette, selected by the "Log Palette" line on the <X> screen, or by the "logmap=" command line parameter: [logmap=0 is 'logmap off' - Hal Lane] logmap=1: for standard logarithmic palette. logmap=-1: "old" logarithmic palette. This variant was the only one used before Fractint 14.0. It differs from logmap=1 in that some colors are not used - logmap=1 "spreads" low color numbers which are unused by logmap=-1's pure logarithmic mapping so that all colors are assigned. logmap=N (>1): Same as logmap=1, but starting from iteration count N. Pixels with iteration counts less than N are mapped to color 1. This is useful when zooming in an area near the lake where no points in the image have low iteration counts - it makes use of the low colors which would otherwise be unused. logmap=-N (<-1): Similar to logmap=N, but uses a square root distribution of the colors instead of a logarithmic one. logmap=2 or -2: Auto calculates the logmap value for maximum effect. Another way to change the 1:1 mapping of iteration counts to colors is to use the "RANGES=" parameter. It has the format: RANGES=aa/bb/cc/dd/... Fractint Version 20.0 Page 85 Iteration counts up to and including the first value are mapped to color number 0, up to and including the second value to color number 1, and so on. The values must be in ascending order. A negative value can be specified for "striping". The negative value specifies a stripe width, the value following it specifies the limit of the striped range. Two alternating colors are used within the striped range. Example: RANGES=0/10/30/-5/65/79/32000 This example maps iteration counts to colors as follows: color iterations ------------------- 0 unused (formula always iterates at least once) 1 1 to 10 2 11 to 30 3 31 to 35, 41 to 45, 51 to 55, and 61 to 65 4 36 to 40, 46 to 50, and 56 to 60 5 66 to 79 6 80 and greater Note that the maximum value in a RANGES parameter is 32767 and [is] the maximum value for the number of iterations [third parameter on the <X> page; maxiter= in .PAR files - Hal Lane] is also 32767 when using RANGES." - Hal Lane ######################### # hallane@earthlink.net <mailto:hallane@earthlink.net> # ######################### ---------------------------------------------------------
-----Original Message----- From: Lee H. Skinner [mailto:skinner@thuntek.net] Sent: Friday, March 30, 2007 9:34 AM To: Fractint and General Fractals Discussion Cc: Philofractal Subject: [philofractal] Re: [Fractint] <Charles> Re: ...big stretches where [there there is] no reason to zoom in...
If the Logmap value is NOT reset these zoomed out images may apparently have many of their pixels rendered in the 'lake' color --
No. Just most of the area outside the lake will have the same color. Setting logmap to 2 will cause an optimization (it will change from 2 to a higher number) of the logmap value for the image. -- ########################################################
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