Image Formats

One and two dimensional images are produced by echelle commands. These images are standard MIDAS frames, sampled in the following spaces:

• pixel-pixel space: corresponds to 2D raw images, with the sampling units PIXEL in both dimensions.
• pixel-order space: corresponds to 2D extracted images, produced by the command EXTRACT/ECHELLE. Unit in the x-axis is PIXEL, unit in the y-axis is ORDER, sequential echelle order number.
• wavelength-order space: corresponds to 2D extracted images, with uniform sampling steps in wavelength, produced by the command REBIN/ECHELLE. Unit in the x-axis is Ångstrøm , unit in the y-axis is ORDER, sequential echelle order number. These images are not standard, in the sense that the descriptors START(1) and NPIX(1) are meaningless. The starting position for each order is defined in the descriptor WSTART, and the number of pixels per order is given by NPTOT, both descriptors are arrays of NPIX(2) elements. This deviation from the standard is due, obviously, to the different spectral range of each echelle order.
• wavelength space: corresponds to 1D images, sampled at constant wavelength steps. These images are produced by the command MERGE/ECHELLE. Unit in the x-axis is Ångstrøm .