Mon, Apr 15, 19

Simple Processing for TRIAD Filter Imaging

Simple Processing for TRIAD Filter Imaging

The TRIAD filter is a revolutionary, new filter that allows for narrowband imaging with one-shot color cameras in just about any light-pollution conditions.

The method presented in this video is just one way to process a TRIAD filter image and you may discover other methods that work equally well. However, if you feel lost and aren’t sure where to start with processing TRIAD images, then this tutorial is definitely for you.

It works by isolating hydrogen-alpha in the red and the oxygen and hydrogen-beta lines in the blue and green channels, allowing you to capture a narrowband image without the need for multiple narrowband filters or a filter wheel.

OPT Triad H-Alpha H-Beta and OIII Narrowband Light Pollution Filter Transmission

In this tutorial, we will give you a short, quick run-through of how to process images shot with the TRIAD filter.

Getting Started


TRIAD Processing Imaging Conditions OPT Parking Lot

The image used for this tutorial was taken from the old OPT parking lot with about a quarter-moon rising, which added even more pollution to the already light-polluted setting.

TRIAD Processing Image Start

Despite intentionally hindering our conditions, TRIAD-filtered images taken directly from the camera will appear fairly dark, showing some stars but not much else. This is a testament to just how well the TRIAD filter blocks light pollution.

Follow the steps in our images below to have a clear path on effectively processing images using the TRIAD filter.

Assessing Image Levels Menu TRIAD Processing Tutorial

Assessing Image TRIAD Processing Tutorial

Since the default image is so dark to the human eye, you’ll need to use some other means to assess the image. This is can be done using the Levels function, which lets you see how dark the image truly is, in terms of color information. Prior to processing, a TRIAD filter image will have a very strong, yet narrow, color range.

Wavelength chart TRIAD Processing Tutorial

This is the result of only letting through a little sliver of light at hydrogen-alpha and another narrow band for the hydrogen-beta and oxygen-III lines. While what is visible on the graph doesn’t seem like much, you’d be surprised how much color can be gleaned from the small ranges of light that the TRIAD allows through.

Camera Raw Filter TRIAD Processing

This tutorial will incorporate some features that are new to Photoshop CC, such as the latest version of the Raw Converter. This latest iteration can be used on any image, whether it’s a DSLR RAW file or not, which is a feature we will make use of later in this tutorial.

RC-Astro GradientXTerminator Plugin

This tutorial also makes use of an after-market Photoshop filter known as the GradientXTerminator plug-in created by RC Astro. This filter costs $50, so if you already have another preferred method of removing gradients from images, that can be substituted instead.

Dedicated astrophotography programs such as PixInsight or Nebulosity have their own built-in gradient removal tools, so if you are already comfortable those, you may not need RC Astro’s filter. However, since GradientXTerminator integrates directly into the Photoshop filter menu, it is useful for more Photoshop-centric workflows, which is why it is being used for this tutorial.

The image seen here is actually the result of several images which were combined to create one. These were aligned and stacked in Nebulosity and then flattened down to the single, final image. These programs are ideal for stacking a large number of images. While Nebulosity and other programs are ideal for stacking, it is possible to do simple stacking in Photoshop if you only have a handful of images to stack. This video will help you with this process:


Getting Started with Curves and Levels


First Curves Menu Selection TRIAD Tutorial

First Curves Aggressive TRIAD Tutorial

Start out with a very aggressive Curve to bring up the information. In doing so, you can start to see some nebulosity. Be careful to not be too aggressive with your Curves, as you don’t want to cut off-color information without good reason.

First Levels Preserve Black Information TRIAD Tutorial

Next step, go to Levels. Bring up the black point while being careful not to lose too much information.

Red Hydrogen-Alpha After First Curves Levels TRIAD Processing Tutorial

As the Levels are adjusted you will start to see the reddish hydrogen coming through very clearly.

Second Curves Bring Out Background TRIAD Tutorial

After this is another round of Curves, this time a bit more subtle than in the first round. The goal is to bring out the background colors.

Second Levels Menu TRIAD Processing Tutorial

Next, go to Levels again. We’re starting to see some gradient in the background. This is because the image was taken with a fairly extreme amount of light pollution in the sky and without the use of flat frames. In this case, taking the “lazy way out” and not using flats means having to deal with more in the way of gradients.

Second Levels Red Channel Black Point TRIAD Processing Tutorial

Second Levels Green Channel Black Point TRIAD Processing Tutorial

Second Levels Blue Channel Black Point TRIAD Processing Tutorial

With this second round of levels, you’ll want to set the black point for each of the three channels individually. In doing so, you will see a slight blue shift in the background, which is a result of the hydrogen-beta and oxygen-III bands being a little broader to encompass both of those wavelengths. This has the consequence of letting in far more in the way of blueish light, while the red channel, which is isolated hydrogen, shows more defined contrast.

Third Curves Brightness Increase TRIAD Tutorial

After this second Levels adjustment, do one more Curve adjustment to get the image moderately bright. In doing so, you will start to see some of the gradient intrude.

Noise Reduction with the Camera Raw Filter


Now, because the image was the product of a color camera, it ultimately had to pass through that camera’s Bayer matrix.

Bayer Matrix RGGB Pattern TRIAD Tutorial

A Bayer matrix is the pattern of filters laid over a sensor’s pixels that make it into a color camera. This consists of a repeating pattern of four pixels in a sequence of red, green, green, and blue. A byproduct of this filter is that only one out of every four pixels picks up red light and the other three-quarters share the blue and green light between them. Any restrictive filtering like the Bayer matrix brings the risk of added noise, and there is some additional noise added by the TRIAD as well. However, anyone who’s shot narrowband images in monochrome knows that noise is just a fact of life when it comes to narrowband filters.

Camera Raw Window TRIAD Processing Tutorial

Camera Raw Window Noise Reduction Detail Luminance Color TRIAD Processing Tutorial

To help remove noise, we can use the Camera Raw filter. The Luminance slider in the Noise Reduction section should be pushed to around 20-25 and the Color slider pushed up a little higher than that. This will clean up a lot of the noise and help correct some small-scale color blotching, which can affect the gradient removal process.

Gradient Reduction with GradientXTerminator


Gradient Removal Select Area TRIAD Processing Tutorial

Next, we will use the GradientXTerminator tool to remove the gradient. Using the Lasso or another selection tool, make a selection around the nebula or central object in your image. Don’t be too concerned with perfection in this step, as it’s not necessary for the gradient removal process to work. In fact, if the entire image is selected it won’t do much good for gradient removal. The area that has been selected reflects the area we want GradientXTerminator to ignore.

Gradient Removal Select Inverse TRIAD Processing Tutorial

Gradient Removal Feather Selection TRIAD Processing Tutorial

Select Inverse and then create a Feathered edge. Choose a Feather of about 20 pixels.

Gradient Removal RC-Astro GradientXTerminator TRIAD Processing Tutorial

The GradientXTerminator menu has a very simple layout. We have Detail: Fine/Medium/Coarse and Aggressiveness: Low/Medium/High. The layout indicated here with Coarse Detail and High Aggressiveness with “Balance background color” checked will provide the best results for this particular image.

Gradient Removal Results TRIAD Processing Tutorial

Running this does a pretty good job of cleaning up the blueshift in the background, as well as the dark lower-right corner and the overly-bright upper-left corner.

More Curves and Levels 


More Curves TRIAD Processing Tutorial

After this, make some additional adjustments to Curves and Levels. Once again, don’t push things too far, as you don’t want to blow out the stars in your image.

More Levels Red TRIAD Processing Tutorial

More Levels Blue TRIAD Processing Tutorial

When adjusting Levels, adjust them for each color channel so that you can fine-tune the exact background color.

More Levels Green TRIAD Processing Tutorial

If the green channel is a little too hot and you have to push it really hard to bring out the color, don’t worry about cutting off data from this channel at this point in the process. There’s not a ton of green out in space, even when viewing with a narrowband filter, meaning that it’s not a terrible thing to let a little bit of it go.

More Curves Second Round TRIAD Processing Tutorial

“Season-to-taste” at this point, making fine adjustments to bring out the faint structure in the hydrogen, which shows up prominently in the red channel. While the green and blue channels look very similar, the blue channel brings in a little bit more of the hydrogen-beta and the green channel pulls in a little bit more of the oxygen.

High Pass Filtering


High Pass Menu TRIAD Processing Tutorial

High Pass TRIAD Processing Tutorial

Fade High Pass Menu TRIAD Processing Tutorial

Fade High Pass Adjustments TRIAD Processing Tutorial

At this point run a High Pass filter at about 40 pixels and then Fade High Pass to Soft Light with about 50%. This allows you to really boost contrast, making everything pop that much more.

Clarity Adjustment in Camera Raw


Detail-Luminance Camera Raw Second TRIAD Processing Tutorial

Next, you’ll want to do one more round of the Camera Raw filter, which can help remove a little bit of residual noise in the background. Adjust Luminance under the Detail tab.

Basic Clarity Camera Raw Second TRIAD Processing Tutorial

Under the Basic menu, use the Clarity slider to really bring out the structures. Be careful, because if you push it too far you may lose Saturation. Boosting Clarity to around 30 or so can give you a really nice result.

Hue and Saturation


Hue Saturation Menu TRIAD Processing Tutorial

Hue Saturation Adjustment TRIAD Processing Tutorial

Lastly, you can adjust Hue and Saturation if you like. While this may not be a completely “finished” image at this point, it’s a testament to the TRIAD filter’s capabilities that so much structure could be pulled out of an image that was considerably darker at the start.




Using the TRIAD filter allows you to achieve amazing results from highly light-polluted locations. Considering the image here was taken in about magnitude 4 skies with a quarter-moon rising, the results from this basic image processing are all the more impressive. With the TRIAD filter, you can achieve results like this under equally bright skies.

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