Well, that depends… mostly on what filter(s) you’re using and what object you’re imaging. If you’re imaging in mono, using narrowband filters, you probably know everything below, and you can get better data and images in worse conditions. But if you’re using a dual, tri or quad-band filter with a color camera and imaging any one of the endless number of Ha & OIII rich objects in the sky, you don’t have to just settle for the endless sea of red nebulosity.
You can’t achieve a true SHO Hubble Palette with these multi-narrowband filters and a color camera, as SII and Ha can’t be separated in the red channel, you can use other palette options and photoshop layering to obtain varying results that you can tweak to your tastes. What I’ll talk about here are the Ha/H+O/O palette and blending that image with an RGB image.
The examples below of the Jellyfish Nebula (IC443) show both subtle and more obvious differences from a regular RGB. All images were created using the same stack of 30, 10 minute exposures (5 hours). After the descriptions of each image is a gallery that you can click on to look at larger versions of the Jellyfish variants and some other out there color options for other object. This doesn’t work well with all objects – M42 was a miserable failure – but it’s worth playing around with those having a decent amount of OIII data.
- Meade Series 6000 80mm APO Refractor
- Meade LX85 Mount
- ZWO ASI071MC Pro
- Radian Telescopes Triad Ultra Quadband filter
A video should be coming soon going over these techniques in more detail if you’re interested. I’ll embed it in this page when I get a chance to make it.
Image 1 – RGB
This image was created using standard processing techniques – Stretching, levels, stretching, levels, minimize stars, noise removal, etc.
Image 2 – H/HO/O
This is where the processing time really lengthens. you’ll use this created
- Stretch the RGB image until you’re happy with the stars and you have some good visibility of the nebula.
- Select color range – highlights, expand the selection and copy them into a new image. I like to create a bottom black layer and paste the stars on top to get better visibility so I can tweak them.
- Copy the Red (Ha) channel and Green (OIII) channel into new 16bit grayscale images, save them and run them through Starnet++.
- After Starnet, copy and assign the Ha image to the Red channel of a new RGB image, and assign the OIII to the Blue channel.
- Copy the Ha image as a new layer on top of the OIII image and reduce the opacity to 50% and merge the layers. Copy this into the green channel of your new RGB image.
- From there you can play with colors using the Selective Color tool in photoshop.
- I also like to stretch the blue channel quite a bit and then run an aggressive noise reduction with the Camera Raw tool on that channel. The red and green channels provide the detail, so you really won’t lose much in sharpness, but you’ll gain a lot in color.
- Once you’re happy with the nebula, you can paste in the stars that you saved in a separate image earlier. I like to set the layer to either Screen, Lighten or Pin Light. Experiment and see what you think looks best. This is definitely not as natural of a look, but it really gives the nebulosity center stage.
Image 3 – A Layered Blend (Screen)
The rest of the images are a blend of the H/HO/O and RGB images using different layer settings in Photoshop. The first is created by using the Screen setting for the layer. This very subtly allows some blues to come through on the edges of the Jellyfish. After pasting, you may want to adjust the opacity of the layer, along with bringing the curves down to avoid blowing out brighter parts of the nebula. As with everything, it’s to taste.
Image 4 – A Layered Blend (Color)
This is a similar process to Image 3, except this time you’ll set the H/HO/O layer to Color. You may find that you can keep the opacity at 100% and no need to reduce the curves in this one. You’ll notice more blue around the edges of the Jellyfish as well as some other areas, but the red will dull slightly. If you want something more vibrant, you can use the Selective Color tool to tweak the reds, or use the layer setting in Image 5 – Hue.
Image 5 – A Layered Blend (Hue)
This is my favorite, and most dramatic of the blended images. The H/HO/O image is simply pasted on top of the RGB image and set to Hue. The blues really come through and the reds transition to more of a fuchsia.
Click the images below for larger versions.
Some other color option examples.
My images aren’t necessarily meant to be a pure representation of what’s in the sky. My skies are too polluted, my time outside and ability to travel too limited, and my brain too easily bored with red to just do a few stretches and send along a cookie cutter image. Some of them end up looking like absolute crap, and some of them surprise me. But three-and-a-half years later, I still learn from each and every one. Enjoy what you’re doing, and make it yours!
Clear Skies, Bleary Eyes – KA