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Topics - Ken Pendlebury

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Gallery / Elephant's Trunk - HST Palette
« on: 2011 September 02 22:11:05 »
Hi folks,

Below is my attempt at the Elephant's Trunk Nebula in HST Narrowband. I had great difficulty getting this image into shape... more than any other I have done. Most of my troubles originated from the weak OIII and SII signals when compared with the very strong Ha signal. When creating a LRGB composite from these signals, the HST palette creates a "very" green image.  The first set of color corrections I made used Photoshop's "Selective color" tool to tame the greens (certainly effective), but the version posted here used the PI curves module (hue) as Niall details here:

Comments and criticism welcome.

Large Size:

Original Size:

Equipment and Exposure Details:


General / Help with Bias
« on: 2011 September 01 20:38:12 »
Hi folks,

I am hoping somebody might be able to help me understand some image behavior that has baffled me...

I am attempting to take bias frames for my camera.  I have gathered the 16-bit frames with the Astroart application and inspected them.  All frames are at an acceptable level (below 1000 ADU).  To verify, I open the same frame in the Nebulosity capture application and it verifies that the images is below 1000 ADU.  When I open this very same image in PI, it shows a mean ADU of 33682!

Obviously integrating these frames as PI sees them creates a terrible bias frame. 

Strangely, when I use Nebulosity to capture the bias frames, PI does indicate that the ADU value is less than 1000.  Astroart uses an ASCOM driver for capture (QHY9 Camera) while Nebulosity uses a native driver.  I'm not sure if this is relevant at all, but though I would mention it.

Any thoughts are appreciated


Gallery / Eastern Veil Bi-Color
« on: 2011 August 07 16:54:48 »
Hi folks,

This is my attempt at a bi-color (Ha & OIII) version of the eastern veil.  Equipment and exposure details can be found by following the link below.

Here is a summary of the processing approach:
  • Stretch Ha and OIII separately to ensure equal contribution to total signal strength
  • Map Ha to Red and OIII to Blue
  • Create false green channel using Pixel math.  Lots of experimentation here, final was (0.45*Ha + 0.55*OIII)
  • Use hue adjustment to fine-tune colors to liking
  • Neutralize background to remove excessive reds (mask over nebula)
  • Perform HDR Wavelets to enhance tendrils
  • Erode stars to minimize noise (Morph module w/ 7 iterations)
  • ACDNR to cleanup some noise

Please let me know if you have suggestions for improvement.  I'm here to learn and this is my first narrowband attempt.

Full Size:

Exposure Details:

Thanks for looking,

Gallery / Melotte 15 (Heart Nebula)
« on: 2010 December 17 14:11:41 »
Hi folks,

I thought I would post my first real try at an emission nebula using some variation of an HaRGB combination technique.  In the spirit of Jack's post, I am hoping this might be a learning experience for me (and others).

I thought the detail turned out well (especially considering the suburban location), but I am not thrilled with the color balance.  Without reciting the entire processing methodology I used, I wanted to layout what I suspect are possible culprits:

1.) I only captured 60 minutes of 5min 2x2 RGB (each) from a suburban location.  I think that the signal might be a bit too weak to obtain proper balancing of colors.
2.) The LRGB method I used is likely suspect:  First I processed the Lum(Ha) to my liking.  Next I used the LRGB module (without L checked) to combine the linear RGB stacks.  This was followed by background neutralization, DBE, color calibration (no structure detection) and finally by MTF.  I had difficulty with BN and CC because the emission nebula covers the entirety of the frame (I was unable to provide a viable reference background).  As such I chose the entire image as the reference (probably a bad idea).

At this point I have a RGB composite that looks very weak.  Using the LRGB combine tool, I add the Ha as Luminance and this turns a very nicely colored image (albeit weak) into a red-pink monstrosity.  I have not yet tried Vincent's methodology ( because I am unsure if capturing RGB at 2x2 will scale well.

Any suggestions are welcome...


General / Heart Nebula Advice
« on: 2010 December 06 21:48:58 »
Hi folks,

I have a couple of questions about processing nebulae (like the heart nebula).  First a bit of data...  I took ~3 hrs of Ha (1x1) data with 1 hr each of RGB (2x2) with intent to use Ha as the luminance channel.

My general approach was to take and process the RGB data and ensure that it has the desired color.  It is a bit difficult to use tools like color balance because nebulous gas covers the entirety of the frame.  This scenario does not allow for the use of a background reference and, as such, the entire frame yields background stars that are a bit too "orange-red".

So... my first question is:

1.) How does one go about balancing colors where there is no "empty" (non-dso) background to reference?

Next, I think I have a fundamental misunderstanding about the Lum channel.  When I arrived on an RGB frame that was ok and had the right shade of red (except as described above), I went to register and combine this with my Ha data.  Using the LRGB combine module, I select the Ha as "L" and apply this to the registered RGB data.  The resultant image has changed the deep red color created in the RGB to a pale salmon color.  I know that combining the Ha with the Red channel can sometimes crate this color, but I didn't know that the Lum channel could change color this drastically.  I think that Juan may have explained to me how this can happen, but it was probably above my head...

2.) So... is there a better way to use Ha data as the Lum and retain color?  Perhaps I am going about this the wrong way entirely.

Thanks for any help,


Gallery / M33, ET and the Flaming Star
« on: 2010 November 12 16:10:33 »
Hi folks,

The links below point to data I captured at the Eldorado Star Party in Texas.  Three beautiful nights of clear crisp skies allowed for a good deal of exposure time.  M33 might be a little over-processed.  This is likely a matter of taste, but I had to darken the background a bit more than I like because applying ACDNR to an over-stretched background lends itself to a "mottled" look of which I am not too fond.  The ET cluster is nice, but can probably use a bit more saturation in the stars.  The flaming star I found a bit hard to frame.  As a result I ended up cutting some of the most interesting parts out...  oh well.

Comments and criticism welcome.  I am always looking to refine my techniques.


ET Cluster:

Flaming Star:


Gallery / M31 with Ha and RGB (No Lum)
« on: 2010 October 13 08:39:08 »
Hi Folks,

Following some advice from Juan, I decided to see what this whole "No Lum" thing was all about.  Since I had time to capture over 7 hours of RGB from a dark sky, I felt that was sufficient to overcome the need for luminance frames.  After this, I was able to add in a couple hours of Ha in order to emphasize the faint HII knots on the outer arms.

Here is the result:

Wide field:


Exposure and Equipment Details:


General / HII Advice
« on: 2010 October 11 08:21:31 »
Hi folks,

I have recently acquired about 7 hrs of 1x1 RGB data of M31.  After processing, I was generally pleased with the result, but thought it lacked proper emphasis of the HII regions.  As such, I collected about 2.5 hrs of Ha data (1200 s ea.).


I am wondering if integration of Ha data for HII emphasis is any different from normal Ha blending.  That is to ask:  should I just experiment with blending the Ha into the red channel with Pixel math?  Or is there a different procedure in this case?

Thanks for any advice,

General / HDRComposition exposure question
« on: 2010 October 07 22:46:15 »
Hi folks,

I think that I would like to try the new HDRComposition on M31, but before I go out and collect data, I have a couple quick questions:

I haven't quite resolved the entire process in my brain and I am wondering if the decreasing exposure times need only apply for Lum or should this pattern be applied to RGB as well.  For example, can I take Lum at 10 min, 5min, 2 min and 30 sec and then a series of RGB all at 5 min?  Will the core be tamed by the Lum channel or will the color combination still blow it out if I don't take smaller increments of RGB (2 min & 30 sec)?

Thanks for any advice,

Off-topic / So many stars...
« on: 2010 September 06 18:32:25 »
Hoping somebody can help here...

Below you can see my first attempt at the crescent nebula.  I am concerned because there are SO MANY stars that they actually drown out the DSO.  Is there a way to tame these stars without affecting the nebula (too much)?  Thanks for any tips.


General / Combining Different Image Scales
« on: 2010 August 06 11:01:43 »

I'm sure this has been discussed before, but I am having difficulty locating a conversation I once read concerning this issue.

If I have a friend who will take 2x2 RGB images at a different image scale than my L images, what is the best way to "match" the images for LRGB combination?  Can the Image Registration Module do this?

RGB taken at 2x2 with QHY9 and 480mm FL Refractor
L taken at 1x1 with QHY9 and 780mm FL Refractor

Thanks for any advice.


Off-topic / Star Damage Question
« on: 2010 June 20 16:08:36 »
Hi Folks,

This has happened in at least 3 images that I have processes with PI.  At Some time during the processing, I seem to be "damaging" larger stars, but only in the cores.  The star halos still look OK.  Tracing this back is a little difficult, because the damage seems to manifest itself as a small "lighter" spot in the star's core during the beginning steps, but is readily apparent when any attempt to saturate the image is made.  HDR Wavelets seems to enhance the core spots, but I am not sure if they are the root cause.

Here are a couple stars from an image of M101 that are representative of the damage I describe above:

If there is any interest or information that can be gleaned by inspecting the full image, the wide field can be found here:

and the crop here:

I have attached my processing steps for M101 and a basic outline is as follows:
  • Calibrate (flats and bias)
  • Debayer
  • Register
  • Stack
  • BG Neutralization
  • DBE x2
  • Color Calibration
  • SCNR for green
  • Masked Stretch (15 iterations)
  • HDR Wavelets
  • Unsharp Mask
  • Curves for Saturation
  • Final Histogram tweak
  • Curves for small contrast boost

Thanks for any help,

Off-topic / HaRGB with OSC
« on: 2010 June 03 11:59:37 »
Hi folks,

I have a OSC camera (QHY8) and I was curious if anyone else has attempted Ha imaging with something similar...

I have read many posts here about various methods by which Ha may be combined with RGB, but was curious about the steps prior to these methods for OSC type cameras.

When using an Ha filter over a Bayer matrix, I assume that only the red pixels actually get any data.  Is it fair to say that in order to get my hands on an Ha image, I would debayer the frame, extract the RGB channels and toss the green and blue (meaning only the red frame is of interest)?  At this point, I think that I would desaturate (extract lum) the red channel in order to prepare it for use in pixel math.

Any thoughts on this roughly outlined process?

I apologize if this has already been asked, but it is difficult to search for terms like "Ha" and "OSC"

Lastly, I have read a lot of chatter about "NB Channel Mixer" modules and the like from last year.  Is pixel math still the accepted way to perform HaRGB combinations in PI 1.6?


R: (1 - k)*$T + k*Ha  where k between 0-1
G: $T
B: (1 - j)*$T + j*Ha where j between 0-1

Thanks for the help,

Gallery / M3 HDR Composition
« on: 2010 May 04 19:52:17 »
Hi folks,

Thought I would share this composition of M3 I put together from data captured last Sunday.  It consists of 5m x 12 (for the base) and then is composed of 150s x 10; 60s x10; 30s x 10 and 10s x10 in order to keep the core resolved and still be able to see some of the less prominent stars in the most distant parts of the cluster. 

Basic Process (have not deviated too far from Harry's tutorials  :P):
- Color Correction
- SCNR (Green)
- Stretch
- HDR Wavelets
- Deconvolution
- Color Saturation
- Final color tweaks

Of note: 
First time I never had to leave PI from calibration to finish!  Awesome!  All of my bias and flat frames were done within PI.

On the wide field image, I have a gradient I cannot tame in the lower right hand corner.  DBE and flats tamed a good deal of the vignetting, but that last spot is left over.  Anyone have any ideas on "tidying up" issues like this?

Wide Field:


Equipment and Exposure Details:

Comments and criticism welcome:


Bug Reports / Clone Stamp - Out of Memory
« on: 2010 April 09 20:52:18 »
Not a big deal, but thought I would report it anyhow.  When opening the Clone Stamp module and changing the radius to 1, an "Out of Memory" dialog pops up.

Changing this value to "2" or higher yields no problems.

Other Info:
OS: Mac 10.6.3
PI: (Snow Leopard Build)

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