Links to other Astrophotographer's websites
Beautiful fine art glass jewelry that draws inspiration from our
universe. Check out their Galaxy collection. The artists are friends of
Oceanside Photo & Telescope
Astronomy Telescopes from Meade, Celestron, TeleVue, Takahashi, accessories and eyepieces, CCD imaging cameras from SBIG and more.
Anacortes Telescope & Wild Bird
Another online astro retailer I like.
A very cool online classified ad and discussion forum service.
Yet another online astro retailer.
LLRGB Processing Flow
Here is my current processing flow for LLRGB images. There are two
guiding principles that to me determine how I proceed with the data. The
first is that the signal-to-noise ratio (SNR) in the data must be
meticulously preserved at every processing step. It is extremely easy to
perform a processing step in such a way that noise is actually
introduced into the data. You worked very hard to acquire your image
data... maximize its potential.
The second principle is that the final image must not look processed.
This is of course very subjective. An example of what would look processed
to me would be the dark halos that appear around stars in over-sharpened
With those principles in mind, here is the procedure by which I
currently process most of my images:
- Calibrate, align and combine raw images for each channel (L, R, G,
- Keep all images, including darks and flats, in floating point format
at all times to preserve SNR in the faint areas.
- Do any necessary de-blooming or bad pixel
repair prior to alignment and combination.
- Use manual two-star alignment for all alignment operations, taking
care not to use saturated stars.
- Use sigma-rejection for all
combination operations, including darks and flats (see above plug-ins
for implementations of this algorithm).
- Do a preliminary alignment of the L, R, G and B channels using
MaxIm. Images should still be in floating-point representation.
- Crop the images such that no image has any
- Perform the following color balancing steps on each color channel
- Multiply the image by the camera gain factor (for my ST-10XME,
with the SBIG standard RGB filters, the
factors are RGB = 1.00:0.88:1.28).
- Measure and subtract the sky foreground level, minus 100 counts as
a pedestal. (For example, if the sky foreground is 257 counts,
subtract 157. This prevents any negative values that would get
- Multiply the image by the atmospheric extinction correction
factor. This is determined by noting the average altitude of the
object for this color channel and looking up the atmospheric
extinction factor in, say, the Handbook of Astronomical Image
Processing. The correction factor is the reciprocal of the
- Subtract the error introduced into the pedestal by the previous
step. (For example, if the correction factor was 114%, the 100-count
pedestal will become 114 counts. 14 counts must be subtracted from the
image to correct for this or improper color balance will result.)
- Combine the channel images into an LRGB color image using MaxIm.
- Optional: If the colored star halos are misaligned (multi-colored), do a precision alignment of the color channel images to the
luminance image using RegiStar, and recombine in MaxIm.
- Boost the saturation to taste.
- Close all but the luminance and LRGB images. Make sure these are
saved in floating-point FITS format as master copies. Perform all
subsequent steps on secondary copies of these two files.
- Perform a DDP-style stretch on the luminance image.
- Set the background level by hand to just below the image background
- Set the mid-point level by mouse-click on a moderately faint part of
the object of interest. This may need to be adjusted by hand.
- Don't do any sharpening as part of DDP. This is accomplished by
selecting the "user" kernel filter, and setting the filter coefficients
to 1.0 in the center, and zeros elsewhere. All we want out of DDP right
now is a non-linear stretch.
- Perform a DDP on the LRGB image using the same parameters as for the
- Boost saturation after DDP if needed. (DDP tends to wash out the
- Now it is finally okay to save the images in something other
than a floating-point format. Save both images in 16-bit TIFF format.
Reason: the DDP operation boosted the contrast in the faint areas such that
there are now large differences in pixel values in these areas. Prior to
this, saving in integer format would have introduced excessive rounding
- Open both the luminance and LRGB TIFF images in PhotoShop.
- Perform a "big unsharp mask" on the luminance image:
- First, drop the output white level to about 200 using the levels
- Invoke the unsharp mask filter. Set the radius to 250 pixels and the
percentage to between 20 and 40.
- Make sure nothing important (e.g., core of galaxy) got clipped. If
it did, undo, drop the white level again, and repeat the filter.
- Perform smaller unsharp masks as desired to increase contrast in
features of interest. I usually do a 100- or 50-pixel radius unsharp
mask, followed perhaps by a 10-pixel radius, all at fairly low
percentages. Again, the image should not "look processed."
- Adjust the levels and gamma to very close to what you would like for
the final image.
- Save this image in 16-bit TIFF format with a new file name.
- Convert the image to 8-bit format, and save in a new file as the
base layer for your final luminance image. (Note: you can leave it in
16-bit format in PhotoShop CS, a major advantage.)
- Do some form of fine sharpening on the 16-bit luminance image. This
could be Lucy-Richardson deconvolution in your program of choice, or
simply some fine unsharp masking. Don't worry about mild mottling or
increased noise showing up in the faint areas... this will be dealt with
- Load the sharpened image into Photoshop.
Convert it to 8-bit format. Select all, copy, and paste it onto your
base layer created above. (Again, you don't need to convert to 8-bit in
- Do the followings steps to blend the
sharpened foreground image with the unsharpened (and thus smoother)
- Use the Select->Color Range command to
select the background areas of the image.
- Feather the selection by a hefty amount
(40-200 pixels, depending on image size and content).
- Make sure the top (sharpened) layer is
selected in the layer window.
- Hit "delete." This will make the background
area of the top layer transparent, allowing the smoother background of
the unsharpened image to show through.
- Be willing to undo and re-do these steps
with different settings, etc., until you have the luminance image
looking the way you want it.
- Save this layered luminance image to a file,
retaining the layers in case you want to adjust it later.
- Flatten the layered luminance image.
- Copy and paste the flattened luminance image
onto the color image you loaded earlier.
- Set the blending mode to "luminosity." This
will apply the color of the background (color) image, while retaining
the brightness information of the luminance image you built.
- You might need to reduce the opacity of the
luminance layer and/or increase the saturation of the color layer to get
the color looking how you want it.
- Season to taste, flatten, and save!
M42 Luminance Processing
M42 has such a huge contrast that I used luminance layering in photoshop,
in addition to DDP stretching, to reduce that range so all of the detail could be seen.
Basically, I created four versions of the image, each stretched to give
detail to increasingly brighter areas. The base layer has detail in the
dimmest portions, but has the core and most of the surrounding area
totally saturated. The next image has the dim areas nearly black, and the
next-brightest part of the nebula in good contrast. Again the core is
saturated. Two more images, working in towards the core, proceed in the
same fashion. The last image has just the trapezium and the small area
right around it in good detail... the rest of that image is nearly black.
In photoshop, you can start with the base layer and then paste the next
image on top of it, and then delete the dim portions of that second image.
This is done using the "select color range" tool, feathering the result
by, say, 100 pixels, and hitting "delete." This lets the dim outer areas
show through from the base layer. The procedure continues in a similar
fashion for the rest of the images -- paste, select, feather, delete. It
takes some fiddling to get the selection and feathering parameters right,
but as you can see it can be made fairly seamless.
This is my current flow for combining H-alpha and RGB
or LRGB images.
- Start with well-processed H-alpha (as grayscale) and RGB images.
Process each separately at first.
- Register the two images.
- Convert the H-alpha image to RGB.
- Delete (make black) the green and blue channels.
- Select all, copy, and paste this red image onto the RGB image.
- Change the blend mode on this layer to "lighten."
- Adjust the histogram (mainly gamma) of the H-alpha layer to bring
its brightness up a bit (gamma ~1.3).
- Flatten this image.
- Select all, copy, and paste this image onto the original
grayscale H-alpha image.
- Change the blend mode to "lighten."
- Flatten this image.
- Select all, copy, and paste this image onto the RGB+H-alpha image.
- Change the blend mode to "luminosity."
- Change the opacity to ~50%.
- Season to taste.
Solar Image Processing
Here is my current processing flow for solar images taken using the
Take a number of individual raw-format images and...
- convert to 16-bit TIFF
- extract only the red channel from each, saving as 16-bit grayscale
- align and combine (average mode) in MaxIm/DL
- save result as 16-bit TIFF
- load in PS and compress the output levels a bit (to avoid clipping
in next step)
- 50 iterations Van Cittert deconvolution in Images Plus, 9x9 PSF
- back in PS, slight (about 10%) unsharp mask at radius 250 to handle
limb darkening, boost contrast on disk
- about 70% unsharp mask at radius 1 to sharpen things up a touch
- adjust levels for detail in photosphere
- convert to 8-bit, save as base layer in a new file
- undo a few steps, adjust levels for chromosphere and prominences
- save as a new file
- open base layer image
- convert edge image to 8-bit, select all, paste onto base layer image
- select main disk using "select color range"
- adjust selection to edge of photosphere
- feather one or two pixels, delete
- re-do the last few steps about five times until it looks right (this
is the trickiest part)
- save layered image to another file (to be able to back-track if
- flatten image, save as a new file
- convert to RGB mode
- duplicate layer, set top layer blend mode to "luminosity"
- add color to bottom layer using curves tool (zero blue, bend red
upward, bend green downward)
- make any final tweaks to luminance (top) layer and color layer
- flatten image
- celebrate with a trip to the refrigerator!
- The New CCD Astronomy, Ron Wodaski