SPIDER: IP (Interpolate

IP - Interpolate - Bilinear

(09/17/06)

PURPOSE: Interpolates an image using bilinear interpolation or a volume using trilinear interpolation.

SEE ALSO

IP T	[Interpolate - Triangular]
FP	[Fourier interpolation \|\|]
FQ	[Filter - Quick Fourier, High, low pass, etc. \|\|]
DC	[Decimate image]

USAGE

.OPERATION: IP

.INPUT FILE: H_PIC001
[Enter the name of the file to be interpolated.]

.OUTPUT FILE: H_IMG024
[Enter the file where the interpolated image is to be kept.]

For 2-D input image:

.ENTER DIMENSIONS, NSAM & NROW: 128,128
[Enter the dimensions of the interpolated image.]

For 3-D input image:

.ENTER DIMENSIONS, NSAM, NROW, & NSLICE: 128,128,1
[Enter the dimensions of the interpolated image.]

[H_PIC001 will then be interpolated to a size of 128 x 128, and the interpolated image will be put into H_IMG024.]

NOTES

This operation can be used for either interpolation or extrapolation.
The output image does not have to have the same proportions (ratio NSAM/NROW) as the input picture.
Only the new X dimension (NSAM) of the output image need be entered. The other dimension(s) will then be computed assuming the same proportions as the input image. For example, let the input image have the size 60x40. Then the sequence
.ENTER DIMENSIONS, NSAM & NROW: 120 will have the same effect as:
.ENTER DIMENSIONS, NSAM & NROW: 120,80
The program works by throwing a new grid onto the image whose boundaries coincide with those of the old grid. Each pixel of the new grid is computed from its old neighbors by bilinear interpolation or triangular interpolation.
Note that for raw data, a reduction in scale by 'IP' results in a loss of S/N ratio, since only a subset of the original points may be used for interpolation. The proper procedure maintaining the original information as much as possible is to apply an appropriate low-pass filtration to the original image (either 'FQ', or for large images design Remez filter using 'FF PLOT' and use 'RC'), and to decimate it using 'DC' operation.