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diff --git a/pkg/images/imgeom/doc/magnify.hlp b/pkg/images/imgeom/doc/magnify.hlp new file mode 100644 index 00000000..8b31817e --- /dev/null +++ b/pkg/images/imgeom/doc/magnify.hlp @@ -0,0 +1,202 @@ +.help magnify Dec98 images.imgeom +.ih +NAME +magnify -- interpolate two dimensional images +.ih +USAGE +.nf +magnify input output xmag ymag +.fi +.ih +PARAMETERS +.ls input +List of one or two dimensional images to be magnified. Image sections are +allowed. Images with an axis containing only one pixel are not magnified. +.le +.ls output +List of output image names. If the output image name is the same as the input +image name then the magnified image replaces the input image. +.le +.ls xmag, ymag +The magnification factors for the first and second image dimensions +respectively. The magnifications need not be integers. Magnifications +greater than 1 increase the size of the image while negative magnifications +less than -1 decrease the size by the specified factor. Magnifications +between -1 and 1 are interpreted as reciprocal magnifications. +.le +.ls x1 = INDEF, x2 = INDEF +The starting and ending coordinates in x in the input image which become +the first and last pixel in x in the magnified image. The values need not +be integers. If indefinite the values default to the first and last pixel +in x of the input image; i.e. a value of 1 and nx. +.le +.ls y1 = INDEF, y2 = INDEF +The starting and ending coordinates in y in the input image which become +the first and last pixel in y in the magnified image. The values need not +be integers. If indefinite the values default to the first and last pixel +in y of the input image; i.e. a value of 1 and ny. +.le +.ls dx = INDEF, dy = INDEF +The intervals between the output pixels in terms of the input image. +The values need not be integers. If these values are specified they +override the magnification factors. +.le +.ls interpolant = "linear" +The interpolant used for rebinning the image. +The choices are the following. +.ls nearest +Nearest neighbor. +.le +.ls linear +Bilinear interpolation in x and y. +.le +.ls poly3 +Third order polynomial in x and y. +.le +.ls poly5 +Fifth order polynomial in x and y. +.le +.ls spline3 +Bicubic spline. +.le +.ls sinc +2D sinc interpolation. Users can specify the sinc interpolant width by +appending a width value to the interpolant string, e.g. sinc51 specifies +a 51 by 51 pixel wide sinc interpolant. The sinc width will be rounded up to +the nearest odd number. The default sinc width is 31 by 31. +.le +.ls lsinc +Look-up table sinc interpolation. Users can specify the look-up table sinc +interpolant width by appending a width value to the interpolant string, e.g. +lsinc51 specifies a 51 by 51 pixel wide look-up table sinc interpolant. The user +supplied sinc width will be rounded up to the nearest odd number. The default +sinc width is 31 by 31 pixels. Users can specify the resolution of the lookup +table sinc by appending the look-up table size in square brackets to the +interpolant string, e.g. lsinc51[20] specifies a 20 by 20 element sinc +look-up table interpolant with a pixel resolution of 0.05 pixels in x and y. +The default look-up table size and resolution are 20 by 20 and 0.05 pixels +in x and y respectively. +.le +.ls drizzle +2D drizzle resampling. Users can specify the drizzle pixel fraction in x and y +by appending a value between 0.0 and 1.0 in square brackets to the +interpolant string, e.g. drizzle[0.5]. The default value is 1.0. +The value 0.0 is increased internally to 0.001. Drizzle resampling +with a pixel fraction of 1.0 in x and y is equivalent to fractional pixel +block summing (fluxconserve = yes) or averaging (flux_conserve = no) if +xmag and ymag are < 1.0. +.le +.le +.ls boundary = "nearest" +Boundary extension type for references to pixels outside the bounds of the +input image. The choices are: +.ls nearest +Use the value of the nearest boundary pixel. +.le +.ls constant +Use a constant value. +.le +.ls reflect +Generate value by reflecting about the boundary. +.le +.ls wrap +Generate a value by wrapping around to the opposite side of the image. +.le +.le +.ls constant = 0. +Constant value for constant boundary extension. +.le +.ls fluxconserve = yes +Preserve the total image flux. +.le +.ls logfile = STDOUT +Log file for recording information about the magnification. A null +logfile may be used to turn off log information. +.le +.ih +DESCRIPTION +The list of input images are expanded or contracted by interpolation +to form the output images. The output image names are specified by the +output list. The number of output image names must be the +same as the number of input images. An output image name may be the same +as the corresponding input image in which case the magnified image replaces +the input image. The input images must be one or two dimensional and each +axis must be of at least length 2 (i.e. there have to be distinct +endpoints between which to interpolate). + +The magnification factor determines the pixel step size or interval. +Positive magnifications are related to the step size as the reciprocal; +for example a magnification of 2.5 implies a step size of .4 and a +magnification of .2 implies a step size of 5. Negative magnifications +are related to the step size as the absolute value; for example a +magnification of -2.2 implies a step size of 2.2. This definition +frees the user from dealing with reciprocals and irrational numbers. +Note that the step size may be specified directly with the parameters +\fIdx\fR and \fIdy\fR, in which case the magnification factor is +not required. + +If fluxconserve = yes, the magnification is approximately flux conserving +in that the image values are scaled by the ratio of the output to the input +pixel areas; i.e dx * dy. + +In the default case with only the magnifications specified the full +image is expanded or contracted. By specifying additional parameters +the size and origin of the output image may be changed. Only those +parameters to be fixed need to be specified and the values of the +remaining parameters are either determined from these values or +default as indicated in the PARAMETERS section. + +The user may select the type of two dimensional interpolation and boundary +extension to be used. Note that the image interpolation is performed on +the boundary extended input image. Thus, boundary extensions which are +discontinuous (constant and wrap) may introduce interpolation errors. +.ih +EXAMPLES +1. To expand an image by a factor of 2.5: + + cl> magnify imagein imageout 2.5 2.5 + +2. To subsample the lines of an image in steps of 3.5: + + cl> magnify imagein imageout dx=3.5 dy=1 + +3. To magnify the central part of an image by 2 into a 11 by 31 image: + +.nf + cl> magnify imagein imageout 2 2 x1=25.3 x2=30.3 \ + >>> y1=20 y2=35 +.fi + +4. To use a higher order interpolator with wrap around boundary extension: + +.nf + cl> magnify imagein imageout 2 2 x1=-10 y1=-10 \ + >>> interpolation=spline3 boundary=wrap +.fi + +It is important to remember that the magnification affects the pixel intervals! +This means that the number of pixels in an expanded image is not simply +a multiple of the original number. The following example illustrates this +point. Begin with an image which is 100 by 10. This means the +x coordinates run between 1 and 100 and the y coordinates run between 1 and +10 with a pixel interval of 1. + +Let's magnify the x axis by 0.5 and the y axis by 2. +The output pixel intervals, in terms of the input pixel intervals, +are then 2 and 0.5. This means the output x pixels are at +1, 3, 5, etc. and output y pixels are at 1, 1.5, 2, 2.5, etc., again in +terms of the input pixel coordinates. The last output x pixel is then +at 99 in the input coordinates and the number of pixels is 50. For the +y axis the last output pixel is at 10 in the input coordinates and the +number of pixels between 1 and 10 in intervals of 0.5 is 19! Thus, the +final image is 50 by 19 and not 50 by 20 which you would get if you +multiplied the axis lengths by the magnification factors. + +A more complex example is given above in which x1=25.3, +x2=30.3, y1=20, and y2=35 with magnification factors of 2. +It is important to understand why the output image is 11 by 31 and +what the pixel coordinates are in terms of the input pixel coordinates. +.ih +SEE ALSO +imshift, blkavg, rotate, imlintran, register, geotran, geomap +.endhelp |