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There are many software packages that can be used to process CCD
images. You can use just one package to process an image but is
often best to use several packages so you can combine the best features of
each one. My normal image processing sequence for deep sky images is:
- Perform dark frame subtraction on all images with
MaximDL
- Align and add all images with MaximDL
to improve the signal to noise ratio
- Use digital development in Image Plus
on the luminance image to bring out the faint detail and avoid
saturating the bright areas
- Perform deconvolution on the luminance image using CCDSharp to
sharpen the fine detail
- Combine the RGB image in Image Plus
and then use digital development to bring out the fine detail
- Combine the luminance and RGB image in
Adobe Photoshop to form an
LRGB image.
- Apply finishing touches in Adobe Photoshop
such as noise reduction, unsharp masking and removing uneven sky
illumination using the
Gradient Xterminator plug in.
For planetary imaging with the webcam it is best to use
Registax
followed by Adobe Photoshop. For a
complete guide to image processing theory and techniques I recommend
purchasing
The
Handbook of Astronomical Image Processing.
MaximDL has many image processing features as well as the ability to
control popular CCD cameras and telescopes. Some of its image
processing features include:
- Dark frame and flat field calibration of multiple images without
having to load all of them into the program. This is essential to
keep memory consumption to a reasonable level as you are often dealing
with tens of files each of which can be many MBs in size.
- Easily aligning several images so that you can add them together to increase the signal
to noise ratio or use them to form an RGB image.
- Removing uneven sky illumination
- Making a mosaic from separate CCD images
- Combining individual red, green and blue images to form a single true colour RGB or LRGB image.
- Several Unsharp Mask routines to enhance detail in the image
- Maximum entropy deconvolution algorithms which can make a dramatic difference to images
that are slightly blurred due to guiding or focusing errors
- Digital Development Processing. This is an algorithm developed by
Dr Kunihiko Okano. It performs a combination stretching and
unsharp masking to simulate the effect of photographic development on
CCD images.
Image Plus has many of the image processing features of MaximDL 4.0 as well
as the ability to control the Canon 10D SLR camera.
- Conversion of Canon RAW image format to TIFF for processing by other
image processing packages.
- Dark frame and flat field calibration of multiple images without
having to load all of them into the program. This is essential to
keep memory consumption to a reasonable level as you are often dealing
with tens of files each of which can be many MBs in size.
- Alignment and addition of multiple images. Image Plus contains
a unique feature for combining images called 'adaptive add'. I
have not see this in any other image processing package.
Adaptive addition sums the images together in such a way that the no
areas of the image become overexposed.
- Unsharp Masking to bring out fine detail in the images. Image
plus contains a large number of Unsharp Masking routines that are all
operated using slider controls and give a preview of the affect on the
image. This makes the routines very easy to use.
- Digital Development or non-linear histogram shaping. I have found
the Digital Development feature in Image Plus much easier to use than
in MaximDL as Image Plus lets you control the key input parameters
using sliders. You can adjust the sliders and get a preview of
the affect on your image, letting you experiment to get the best image
result very easily.
- Combining individual red, green and blue images to form a single true colour RGB or LRGB image.
I have found that combining the RGB images in Image Plus using a ratio
of 2.3, 1.0, 1.7 respectively produces a true colour image that only
needs minor (if any) colour adjustment in Adobe Photoshop. These
ratios are specific to my SBIG ST2000XM and colour filter combination.
Ratios for other camera and filter combinations will be different.
Image Plus comes with a set of instructional videos on CD or DVD which
guide you through the application of its image processing routines.
Registax
is freeware software which can process AVI files captured by webcams.
A planetary imager may capture an AVI file of a minute's duration or more. It
will contain 100s or 1000s of images of the planet. Registax can
sort through these images, automatically picking the ones with the most
detail . It can then sum these together to produce a single image with a
much higher signal to noise ratio. Registax also contains some useful image
processing routines that can be used to enhance the detail in the summed
image. For example it contains a very powerful unsharp mask
routine.
Adobe Photoshop is the indispensable tool of the CCD imager. Once I have
used MaximDL or Image Plus for the initial processing steps I use Adobe
Photoshop to complete the job. The main features I use in Photshop are:
- Composing the LRGB or LLRGB image from the luminance and RGB images.
- Unsharp Masking. Photoshop contains a very easy to control
unsharp mask routine. It lets you adjust the key parameters
using sliders and gives you a preview of the affect on your image in
real time. This makes it very easy to use.
- Adjusting colour balance and brightness levels of selected areas of the
images. This is very useful for stretching the outer, fainter areas
of a galaxy without overexposing the core.
- Noise reduction. Adobe Photoshop has a number of excellent
noise reduction filters
- Combining images to form a mosaic
- Producing time lapsed animations.
- Removing uneven sky illumination using the
Gradient Xterminator plug in
A good guide to the use of Adobe Photoshop on astronomical images can
be found here.
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