 |
|
|
|
|
|
When we are rested after a night's worth of imaging, our work
has only just begun. We have to process all the raw data and
turn it into completed images. Once bias subtraction, dark
subtraction, and flat fielding have been carried out in MaxIM
DL/CCD or Mira, and hot pixels and gamma ray hits have been
corrected, the resulting images are processed in a variety of
programs, such as ABFilter, Mira, MaxIM DL, and CCDSharp. The
processed raw FITS images are converted into TIFF images and
exported to Photoshop 7.01. Mira and MaxIm DL/CCD can register
(combine) images better than PhotoShop so that stars will not
overlap each other and useful scientific data is preserved.
However, for quick tri-color imaging, it is sometimes faster and
easier to register images in PhotoShop. Once PhotoShop has
received three TIFF images representing red, green, and blue
equivalents for a color astrophotograph, they are then combined
into an RGB image in PhotoShop using its merge image routine;
or, MaxIM DL can be used for making RGB or LRGB color images.
The resultant color image will often have a red, green, or blue
border, because one or more of the tri-color images will be
considerably shifted with respect to the others. The color image
can now be adjusted for good color balance, size, contrast, and
brightness. It can be cropped or sharpened. There are an
infinite number of routines that can be run on it.
Another new technique uses a Luminance image combined with the
red, green, and blue images to produce a final color picture.
The Luminance (L) image is a high quality, long exposure black &
white image taken through a clear filter or through an open slot
in the filter wheel. This is then combined with shorter
exposures through the colored filters to give the final image.
The L image provides most of the image data, especially the high
resolution image detail and the faint image detail. The color
images need only be good enough to provide accurate color data
for the Luminance technique to assign the proper color rendition
to the final picture. In this way, the problem of long exposures
through multiple color filters is somewhat obviated. This
technique has gained popularity in recent years, and some
fabulous amateur images have been obtained with this technique.
One has to start with a well exposed, sharp black & white image.
The color images may even be "binned" to a lower resolution than
the Luminance image. However, this technique still requires
considerable work to produce good results, and considerable
computer finesse is required. Our initial experience with the
Luminance technique have been favorable, and we recommend trying
it using the latest version of MaxIm DL or PhotoShop. |
|
|
BACK |
NEXT |
|
Back to Top | Essay List |
|
