{"id":55282,"date":"2024-02-24T08:28:00","date_gmt":"2024-02-24T08:28:00","guid":{"rendered":"http:\/\/1cbeb69c-6f6e-4370-b39d-070c8d98cb5c"},"modified":"2024-02-24T09:33:48","modified_gmt":"2024-02-24T09:33:48","slug":"dark-frames-master-them-with-our-step-by-step-guide-and-become-an-astrophotography-expert","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/rss_feed\/dark-frames-master-them-with-our-step-by-step-guide-and-become-an-astrophotography-expert\/","title":{"rendered":"Dark frames? Master them with our step-by-step guide and become an astrophotography expert"},"content":{"rendered":"

How to add dark frames to cut down noise in your DSLR deep-sky images <\/p>

By Charlotte Daniels\n <\/p>

Published: Saturday, 24 February 2024 at 08:28 AM<\/p>

\n\n

To maximise the impact of deep-sky images, boosting the signal-to-noise ratio is key, and dark frames can help you do this successfully.<\/p>

In astrophotography, \u2018signal\u2019 is the light emitted from a deep-sky object \u2013 for example, a galaxy<\/a> or nebula<\/a> \u2013 while the \u2018noise\u2019 is produced by our camera\u2019s internal systems.<\/p>

Because we use long exposures in astrophotography<\/a>, our camera sensors start to warm up and introduce thermal and electronic noise into our images.<\/p>

This noise shows up as grainy artefacts that, as we start to stretch our data, can become noticeable and disruptive.<\/p>

Our unprocessed image of the Sadr and Crescent Nebula region, showing unwanted noise artefacts. During the same imaging session we captured 20\u201330 dark frames. Credit: Charlotte Daniels<\/figcaption><\/figure>
While all cameras will produce noise to some extent, DSLRs are particularly susceptible, because they don\u2019t have in-built cooling systems like dedicated deep-sky imaging cameras do.\u00a0<\/p>
One way that astrophotographers combat noise is to take lots of images of targets, known as \u2018light frames\u2019, and then stack them on top of each other.<\/p>
This helps to boost the signal, but doesn\u2019t directly remove the noise of our camera sensors.<\/p>
This is where dark frames come in.<\/p>
**Dark frames explained<\/strong><\/h2>** $\"A$
A stacked master dark frame. Credit: Steve Richards<\/figcaption><\/figure>
Put simply, dark frames capture the random thermal and electronic noise of the camera sensor and, via stacking<\/a> software, allow us to subtract it.<\/p>
This reduces the noise in our image, to give us a helping hand for processing.<\/p>
The good news is that dark frames are arguably the easiest calibration frame to take and can offer significant improvements in noise reduction.<\/p>
Dark frames are simply taken at the same exposure length, temperature and ISO as our light frames.<\/p>
That is, we take them during an imaging session simply by popping our lens cap or telescope cap on.<\/p>
The output will appear to be a black frame, but of course within that frame is the same sensor noise that is in our light frames, which is important!<\/p>
**Step-by-step<\/strong><\/h2>** $\"dark$
In Photoshop, open the stacked image and use Levels to stretch the data in the RGB channels. You\u2019ll notice noise starting to appear<\/figcaption><\/figure>
To show how it\u2019s done, let\u2019s go through how we added dark frames to our processing workflow for a DSLR widefield image of the Sadr<\/a> and Crescent Nebula<\/a> regions of Cygnus<\/a>.<\/p>
In the \u2018Before\u2019 image at the top of this article, you can see our unprocessed image stacked using DeepSkyStacker (DSS).<\/p>
We opened this image in Photoshop and used the Levels<\/em><\/strong> function to stretch the data (click ***Image > Adjustments > Levels<\/em><\/strong>).<\/p>***
In the Levels window, we used the dropdown menu to select between the red, green and blue (RGB) channels, dragging the anchor points until they met the histogram (highlighted in the image above).\u00a0<\/p>
We performed this step multiple times, each time re-clicking on the ***Levels<\/em><\/strong> icon to reset the histogram and bring up a new adjustment window.<\/p>***
***Our histogram widened each time as the data \u2018stretched\u2019.<\/p>***
***However, we weren\u2019t able to stretch the data much before we saw the tell-tale grainy effects of noise.<\/p>***
***We zoomed into a region of the Butterfly Nebula to show this clearly (highlighted in the image above).<\/p>***
***It was then time to restack using our dark frames.<\/p>***
***$\"dark$*** Using DeepSkyStacker<\/a>, open the file again. Restack the image, but this time click on Dark Files<\/em><\/strong> to add in the dark frames<\/figcaption><\/figure>
Heading back to DSS, we re-added our light frames, then clicked on ***Dark Files<\/em><\/strong> (highlighted, Screenshot 2).<\/p>***
***We navigated to where we had saved our DSLR flat frames and selected them all (pressing Ctrl A simultaneously).<\/p>***
After that, we clicked ***Check all<\/em><\/strong>.<\/p>***
***Our dark files now appeared as registered, next to our light frames, in the bottom window of DSS (highlighted in the image above).<\/p>***
***Our dark frames had a red tinge to them, as you can see in the image above.<\/p>***
This was because we used an astro-modified DSLR in which the red spectrum filter had been removed (this allows hydrogen-alpha light to hit the sensor, one of the key wavelengths emitted by nebulae).\u00a0<\/p>
***We then reprocessed our image with the dark frames added.<\/p>***
***Loading our new image in Photoshop, we performed the same data stretch that we did previously, using the*** ***Levels<\/a> function.<\/p>***
$\"dark$
With your dark frames now included, return to Photoshop to adjust the colour balance and make other tweaks until you\u2019re happy with the final result<\/figcaption><\/figure>
This time, there was noticeably less noise in the same region of the Butterfly Nebula (highlighted, Screenshot 3).<\/p>
Finally, we adjusted the colour balance (Image > Adjustment > Colour Balance<\/em><\/strong>) and used noise reduction (***Filter > Noise > Reduce Noise<\/em><\/strong>).<\/p>***
We applied the median filter (click Filter > Noise > Median<\/em><\/strong>) and the colour range function (click ***Select > Colour Range<\/em><\/strong>) to reduce the size and impact of the stars, allowing the nebulous details to come through.<\/p>***
***$\"dark$ <\/figure>*****Dark frames in astrophotography: 3 quick tips<\/strong><\/h2>**Take dark images at the start or end of your imaging session, using all the same settings as your light frames.<\/li>
Aim for 20\u201330 dark frames per image \u2013 more than this won\u2019t result in a noticeable improvement.<\/li>
For DSLRs, add a cap to the viewfinder while shooting darks to stop stray light entering and reaching the sensors.<\/li><\/ol>
***Are you an astrophotographer? Don’t forget to*** ***send us your images<\/a>.<\/em><\/strong><\/p> <\/body><\/html>\n***
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How to add dark frames to cut down noise in your DSLR deep-sky images <\/p>\n","protected":false},"author":24,"featured_media":55283,"template":"","categories":[34],"acf":{"readingTimeMinutes":"5"},"uagb_featured_image_src":{"full":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2024\/02\/dark-frames-master-them-with-our-step-by-step-guide-and-become-an-astrophotography-expert.jpg",1200,834,false],"thumbnail":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2024\/02\/dark-frames-master-them-with-our-step-by-step-guide-and-become-an-astrophotography-expert-150x150.jpg",150,150,true],"medium":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2024\/02\/dark-frames-master-them-with-our-step-by-step-guide-and-become-an-astrophotography-expert-300x209.jpg",300,209,true],"medium_large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2024\/02\/dark-frames-master-them-with-our-step-by-step-guide-and-become-an-astrophotography-expert-768x534.jpg",768,534,true],"large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2024\/02\/dark-frames-master-them-with-our-step-by-step-guide-and-become-an-astrophotography-expert-1024x712.jpg",800,556,true],"1536x1536":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2024\/02\/dark-frames-master-them-with-our-step-by-step-guide-and-become-an-astrophotography-expert.jpg",1200,834,false],"2048x2048":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2024\/02\/dark-frames-master-them-with-our-step-by-step-guide-and-become-an-astrophotography-expert.jpg",1200,834,false]},"uagb_author_info":{"display_name":"importmanagerhub@sprylab.com","author_link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/author\/importmanagerhubsprylab-com\/"},"uagb_comment_info":0,"uagb_excerpt":"How to add dark frames to cut down noise in your DSLR deep-sky images","_links":{"self":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/rss_feed\/55282"}],"collection":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/rss_feed"}],"about":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/types\/rss_feed"}],"author":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/users\/24"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/media\/55283"}],"wp:attachment":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/media?parent=55282"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/categories?post=55282"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}

Our unprocessed image of the Sadr and Crescent Nebula region, showing unwanted noise artefacts. During the same imaging session we captured 20\u201330 dark frames. Credit: Charlotte Daniels<\/figcaption><\/figure>
While all cameras will produce noise to some extent, DSLRs are particularly susceptible, because they don\u2019t have in-built cooling systems like dedicated deep-sky imaging cameras do.\u00a0<\/p>
One way that astrophotographers combat noise is to take lots of images of targets, known as \u2018light frames\u2019, and then stack them on top of each other.<\/p>
This helps to boost the signal, but doesn\u2019t directly remove the noise of our camera sensors.<\/p>
This is where dark frames come in.<\/p>
**Dark frames explained<\/strong><\/h2>** $\"A$
A stacked master dark frame. Credit: Steve Richards<\/figcaption><\/figure>
Put simply, dark frames capture the random thermal and electronic noise of the camera sensor and, via stacking<\/a> software, allow us to subtract it.<\/p>
This reduces the noise in our image, to give us a helping hand for processing.<\/p>
The good news is that dark frames are arguably the easiest calibration frame to take and can offer significant improvements in noise reduction.<\/p>
Dark frames are simply taken at the same exposure length, temperature and ISO as our light frames.<\/p>
That is, we take them during an imaging session simply by popping our lens cap or telescope cap on.<\/p>
The output will appear to be a black frame, but of course within that frame is the same sensor noise that is in our light frames, which is important!<\/p>
**Step-by-step<\/strong><\/h2>** $\"dark$
In Photoshop, open the stacked image and use Levels to stretch the data in the RGB channels. You\u2019ll notice noise starting to appear<\/figcaption><\/figure>
To show how it\u2019s done, let\u2019s go through how we added dark frames to our processing workflow for a DSLR widefield image of the Sadr<\/a> and Crescent Nebula<\/a> regions of Cygnus<\/a>.<\/p>
In the \u2018Before\u2019 image at the top of this article, you can see our unprocessed image stacked using DeepSkyStacker (DSS).<\/p>
We opened this image in Photoshop and used the Levels<\/em><\/strong> function to stretch the data (click ***Image > Adjustments > Levels<\/em><\/strong>).<\/p>***
In the Levels window, we used the dropdown menu to select between the red, green and blue (RGB) channels, dragging the anchor points until they met the histogram (highlighted in the image above).\u00a0<\/p>
We performed this step multiple times, each time re-clicking on the ***Levels<\/em><\/strong> icon to reset the histogram and bring up a new adjustment window.<\/p>***
***Our histogram widened each time as the data \u2018stretched\u2019.<\/p>***
***However, we weren\u2019t able to stretch the data much before we saw the tell-tale grainy effects of noise.<\/p>***
***We zoomed into a region of the Butterfly Nebula to show this clearly (highlighted in the image above).<\/p>***
***It was then time to restack using our dark frames.<\/p>***
***$\"dark$*** Using DeepSkyStacker<\/a>, open the file again. Restack the image, but this time click on Dark Files<\/em><\/strong> to add in the dark frames<\/figcaption><\/figure>
Heading back to DSS, we re-added our light frames, then clicked on ***Dark Files<\/em><\/strong> (highlighted, Screenshot 2).<\/p>***
***We navigated to where we had saved our DSLR flat frames and selected them all (pressing Ctrl A simultaneously).<\/p>***
After that, we clicked ***Check all<\/em><\/strong>.<\/p>***
***Our dark files now appeared as registered, next to our light frames, in the bottom window of DSS (highlighted in the image above).<\/p>***
***Our dark frames had a red tinge to them, as you can see in the image above.<\/p>***
This was because we used an astro-modified DSLR in which the red spectrum filter had been removed (this allows hydrogen-alpha light to hit the sensor, one of the key wavelengths emitted by nebulae).\u00a0<\/p>
***We then reprocessed our image with the dark frames added.<\/p>***
***Loading our new image in Photoshop, we performed the same data stretch that we did previously, using the*** ***Levels<\/a> function.<\/p>***
$\"dark$
With your dark frames now included, return to Photoshop to adjust the colour balance and make other tweaks until you\u2019re happy with the final result<\/figcaption><\/figure>
This time, there was noticeably less noise in the same region of the Butterfly Nebula (highlighted, Screenshot 3).<\/p>
Finally, we adjusted the colour balance (Image > Adjustment > Colour Balance<\/em><\/strong>) and used noise reduction (***Filter > Noise > Reduce Noise<\/em><\/strong>).<\/p>***
We applied the median filter (click Filter > Noise > Median<\/em><\/strong>) and the colour range function (click ***Select > Colour Range<\/em><\/strong>) to reduce the size and impact of the stars, allowing the nebulous details to come through.<\/p>***
***$\"dark$ <\/figure>*****Dark frames in astrophotography: 3 quick tips<\/strong><\/h2>**Take dark images at the start or end of your imaging session, using all the same settings as your light frames.<\/li>
Aim for 20\u201330 dark frames per image \u2013 more than this won\u2019t result in a noticeable improvement.<\/li>
For DSLRs, add a cap to the viewfinder while shooting darks to stop stray light entering and reaching the sensors.<\/li><\/ol>
***Are you an astrophotographer? Don’t forget to*** ***send us your images<\/a>.<\/em><\/strong><\/p> <\/body><\/html>\n***
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How to add dark frames to cut down noise in your DSLR deep-sky images <\/p>\n","protected":false},"author":24,"featured_media":55283,"template":"","categories":[34],"acf":{"readingTimeMinutes":"5"},"uagb_featured_image_src":{"full":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2024\/02\/dark-frames-master-them-with-our-step-by-step-guide-and-become-an-astrophotography-expert.jpg",1200,834,false],"thumbnail":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2024\/02\/dark-frames-master-them-with-our-step-by-step-guide-and-become-an-astrophotography-expert-150x150.jpg",150,150,true],"medium":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2024\/02\/dark-frames-master-them-with-our-step-by-step-guide-and-become-an-astrophotography-expert-300x209.jpg",300,209,true],"medium_large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2024\/02\/dark-frames-master-them-with-our-step-by-step-guide-and-become-an-astrophotography-expert-768x534.jpg",768,534,true],"large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2024\/02\/dark-frames-master-them-with-our-step-by-step-guide-and-become-an-astrophotography-expert-1024x712.jpg",800,556,true],"1536x1536":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2024\/02\/dark-frames-master-them-with-our-step-by-step-guide-and-become-an-astrophotography-expert.jpg",1200,834,false],"2048x2048":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2024\/02\/dark-frames-master-them-with-our-step-by-step-guide-and-become-an-astrophotography-expert.jpg",1200,834,false]},"uagb_author_info":{"display_name":"importmanagerhub@sprylab.com","author_link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/author\/importmanagerhubsprylab-com\/"},"uagb_comment_info":0,"uagb_excerpt":"How to add dark frames to cut down noise in your DSLR deep-sky images","_links":{"self":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/rss_feed\/55282"}],"collection":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/rss_feed"}],"about":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/types\/rss_feed"}],"author":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/users\/24"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/media\/55283"}],"wp:attachment":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/media?parent=55282"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/categories?post=55282"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}

Dark frames in astrophotography: 3 quick tips<\/strong><\/h2>Take dark images at the start or end of your imaging session, using all the same settings as your light frames.<\/li>Aim for 20\u201330 dark frames per image \u2013 more than this won\u2019t result in a noticeable improvement.<\/li>