{"id":32908,"date":"2022-06-16T00:00:00","date_gmt":"2022-06-16T00:00:00","guid":{"rendered":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/?post_type=purple_issue&#038;p=32908"},"modified":"2022-07-12T14:59:28","modified_gmt":"2022-07-12T14:59:28","slug":"processing-removing-stars-from-a-deep-sky-nebula-target","status":"publish","type":"post","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/2022\/06\/16\/processing-removing-stars-from-a-deep-sky-nebula-target\/","title":{"rendered":"Processing: Removing stars from a deep-sky nebula target"},"content":{"rendered":"\n<h5 class=\"has-text-align-center\"><span class=\"has-inline-color has-ccp-green-color\">PROCESSING<\/span><\/h5>\n\n<h2 class=\"has-text-align-center article-full-subhead\">Removing stars from a deep-sky nebula target <\/h2>\n\n<p class=\"has-text-align-center intro\">Use a Photoshop plug-in to eliminate stars in an image of the Statue of Liberty Nebula <\/p>\n\n<ul class=\"no-tts wp-block-purple-slider\" data-autoplay=\"true\" data-speed=\"300\" data-effect=\"fade\"><li class=\"no-tts blocks-gallery-item\"><figure><img src=\"https:\/\/dj9jqhxgw9833.cloudfront.net\/uploads\/sites\/77\/2022\/06\/97a2eb77-aac6-4629-8c3a-deb214a04025.jpg\" alt=\"\" data-id=\"32901\" data-link=\"https:\/\/c01.purpledshub.com\/bbcskyatnight\/97a2eb77-aac6-4629-8c3a-deb214a04025\/\"\/><figcaption>A starless image of NGC 3576 shows why the technique of omitting stars during processing can bring out vivid nebulosity in narrowband images&#8230;<\/figcaption><\/figure><\/li><li class=\"no-tts blocks-gallery-item\"><figure><img src=\"https:\/\/dj9jqhxgw9833.cloudfront.net\/uploads\/sites\/77\/2022\/06\/706720b7-b3a1-4fde-ad58-ca18b5f187a4.jpg\" alt=\"\" data-id=\"32902\" data-link=\"https:\/\/c01.purpledshub.com\/bbcskyatnight\/706720b7-b3a1-4fde-ad58-ca18b5f187a4\/\"\/><figcaption>&#8230; and you still have the option of adding the stars back in<\/figcaption><\/figure><\/li><\/ul>\n\n<p class=\"has-drop-cap article-full-body sans-serif\">With the exception of targets like open clusters, stars are generally not the main feature of astro images. In fact, their presence can hinder us from teasing out nebulae and similar objects of interest. While some programs, like Photoshop, offer techniques to partly get around this, a new plug-in makes it much easier. In this article, I will look at the benefits of using StarXTerminator. <\/p>\n\n<p class=\"article-full-body sans-serif\">The plug-in StarXTerminator, by Russell Croman, has been trained to recognise and eliminate stars from an image, by using \u2018machine learning\u2019 (artificial intelligence). Once these have been removed, the image can be processed with full attention paid to the target. When the processing is complete, the stars can be put back in, or left out (see images, above). <\/p>\n\n<p class=\"article-full-body sans-serif\">The starless software revolution itself began with StarNet++, a free script for PixInsight. Several years later, StarXTerminator, a commercial plug-in, built by Croman\u2019s RC Astro, was introduced for Photoshop (and PixInsight). The software is compatible with Windows,<span> macOS and Linux operating systems, and a free 30-day trial is offered (see <\/span><a href=\"https:\/\/www.rc-astro.com\/resources\/StarXTerminator\" data-type=\"URL\" data-id=\"https:\/\/www.rc-astro.com\/resources\/StarXTerminator\">www.rc-astro.com\/resources\/StarXTerminator<\/a>).<\/p>\n\n<p class=\"article-full-body sans-serif\">Why are stars such a challenge? For starters they are already bright, so you can damage them by \u2018stretching\u2019 (boosting) dimmer elements of the picture. Also, unlike the rest of the image, stars do not require sharpening or noise reduction \u2013 the removal of unwanted artefacts. If you are trying to process nebulae that lie within the Milky Way, it can be tricky to enhance their dim tendrils due to the stars in the field. You\u2019ll find that removing the stars makes processing so much easier. <\/p>\n\n<h5 class=\"article-subhead\"><strong>Making life easier <\/strong><\/h5>\n\n<p class=\"article-full-body sans-serif\">In the past, the process of separating stars from the rest of the image was achieved by using a \u2018mask\u2019.<span> Think of the way a house painter uses masking tape to protect wood trim where new colour is unwanted.<\/span> Likewise, applying a virtual mask to an image allows the processor to protect specific elements (eg, stars), so that work performed on other elements doesn\u2019t adversely affect them. This may include noise<span>&nbsp;reduction, sharpening and colour saturation. While masks do this quite well, Photoshop doesn\u2019t offer a way to make a star mask. In the past, Photoshop \u2018Actions\u2019 \u2013 automated sets of procedures \u2013 could be created by advanced users to select the stars, but these involved multiple iterations of several processes and only did a fair job. The StarXTerminator plug-in for Photoshop removes stars at the press of a button!<\/span><\/p>\n\n<figure class=\"no-tts wp-block-image is-style-default\"><img loading=\"lazy\" width=\"1231\" height=\"742\" src=\"https:\/\/dj9jqhxgw9833.cloudfront.net\/uploads\/sites\/77\/2022\/06\/67cad173-b529-41b4-8978-7573debca10b.jpg\" alt=\"\" class=\"no-tts wp-image-32903\" srcset=\"https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/06\/67cad173-b529-41b4-8978-7573debca10b.jpg 1231w, https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/06\/67cad173-b529-41b4-8978-7573debca10b-300x181.jpg 300w, https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/06\/67cad173-b529-41b4-8978-7573debca10b-1024x617.jpg 1024w, https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/06\/67cad173-b529-41b4-8978-7573debca10b-768x463.jpg 768w\" sizes=\"(max-width: 1231px) 100vw, 1231px\" \/><figcaption> Screenshot 1: the topmost layer of the stack contains only the image\u2019s stars <\/figcaption><\/figure>\n\n<p class=\"article-full-body sans-serif\">After purchasing or downloading the free trial of StarXTerminator, the files must be placed in Photoshop\u2019s \u2018Plug-ins\u2019 folder per the instructions in the included PDF. After opening the plug-in within Photoshop\u2019s \u2018Filter\u2019 menu (\u2018RC-Astro\u2019) and entering the key sent by email, you\u2019ll need to download the latest version of the neural network by clicking \u2018Download AI\u2019. At the time of writing, Version 9 had just been released. With each revision, the neural network is trained further with image data from different optical systems. This makes the program better at recognising stars of all shapes and sizes, and preventing damage to non-stellar structures. <\/p>\n\n<p class=\"article-full-body sans-serif\">While it\u2019s recommended that you run StarXTerminator in the workflow, it does a great job at any stage, even on final images. With a TIFF image open in Photoshop, you can duplicate the background layer twice. <\/p>\n\n<p class=\"article-full-body sans-serif\">From the \u2018Filter\u2019 menu, run StarXTerminator on the top layer. Duplicate this layer, then make it invisible by turning off its \u2018eyeball\u2019 icon. Next, set the lower, duplicate starless layer\u2019s blend mode to \u2018Subtract\u2019, and merge this layer with the one below using the keyboard command \u2018Ctrl + E\u2019, or the \u2018Merge Down\u2019 command in the \u2018Layers\u2019 menu. This is now the layer with the stars alone. Next, drag it to the top and set the blend mode to \u2018Linear Dodge (Add)\u2019 (Screenshot 1). <\/p>\n\n<figure class=\"no-tts wp-block-image is-style-default\"><img loading=\"lazy\" width=\"1231\" height=\"743\" src=\"https:\/\/dj9jqhxgw9833.cloudfront.net\/uploads\/sites\/77\/2022\/06\/b6b82041-9ad8-441c-b741-e1d93a70b8e2.jpg\" alt=\"\" class=\"no-tts wp-image-32904\" srcset=\"https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/06\/b6b82041-9ad8-441c-b741-e1d93a70b8e2.jpg 1231w, https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/06\/b6b82041-9ad8-441c-b741-e1d93a70b8e2-300x181.jpg 300w, https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/06\/b6b82041-9ad8-441c-b741-e1d93a70b8e2-1024x618.jpg 1024w, https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/06\/b6b82041-9ad8-441c-b741-e1d93a70b8e2-768x464.jpg 768w\" sizes=\"(max-width: 1231px) 100vw, 1231px\" \/><figcaption>Screenshot 2: the \u2018Starless\u2019 middle layer can be enhanced with various adjustments and filters to accentuate the deep-sky target <\/figcaption><\/figure>\n\n<figure class=\"no-tts wp-block-image is-style-default\"><img loading=\"lazy\" width=\"1231\" height=\"764\" src=\"https:\/\/dj9jqhxgw9833.cloudfront.net\/uploads\/sites\/77\/2022\/06\/48d9ceca-69a1-47ed-92fe-ecfd0230c87f.jpg\" alt=\"\" class=\"no-tts wp-image-32905\" srcset=\"https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/06\/48d9ceca-69a1-47ed-92fe-ecfd0230c87f.jpg 1231w, https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/06\/48d9ceca-69a1-47ed-92fe-ecfd0230c87f-300x186.jpg 300w, https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/06\/48d9ceca-69a1-47ed-92fe-ecfd0230c87f-1024x636.jpg 1024w, https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/06\/48d9ceca-69a1-47ed-92fe-ecfd0230c87f-768x477.jpg 768w\" sizes=\"(max-width: 1231px) 100vw, 1231px\" \/><figcaption> Screenshot 3: a contrast-enhancing \u2018Curves\u2019 adjustment to the \u2018Starless\u2019 layer can make the nebula pop <\/figcaption><\/figure>\n\n<p class=\"article-full-body sans-serif\">You should now have three layers: the original \u2018Background\u2019 photo (bottom), the \u2018Starless\u2019 version (middle) and the stars themselves, \u2018Stars only\u2019 (top).<span> To work on the \u2018Starless\u2019 layer, activate it by clicking on it, and be sure the \u2018eyeball\u2019 icon is switched on. You may wish to briefly turn off the \u2018Stars only\u2019 layer to get a better look at what you\u2019re doing (Screenshot 2).<\/span><\/p>\n\n<p class=\"article-full-body sans-serif\">With the stars out of the way, the nebula or galaxy in the middle layer can be enhanced in various ways.<span> Screenshot 3 shows a \u2018Curves\u2019 adjustment, which is used to boost a nebula\u2019s brightness and contrast.<\/span> When the processing is complete, the layers are \u2018Flattened\u2019 to include the stars, or not: it\u2019s your choice!<\/p>\n\n<section class=\"wp-block-uagb-section uagb-section__wrap uagb-section__background-color uagb-block-0e16eda7-4e6b-4951-8f43-2d5021b7d747 article-boxout\"><div class=\"uagb-section__overlay\"><\/div><div class=\"uagb-section__inner-wrap\">\n<h5 class=\"article-subhead\">3 QUICK TIPS <\/h5>\n\n\n\n<p class=\"article-full-body sans-serif\"><strong>1. <\/strong>Drag and drop the background layer to the \u2018+\u2019 sign in the \u2018Layers\u2019 panel (twice) to duplicate it before applying StarXTerminator. <\/p>\n\n\n\n<p class=\"article-full-body sans-serif\"><strong>2. <\/strong>If your final image will be starless, you can apply StarXTerminator directly to it without the need for additional layers. <\/p>\n\n\n\n<p class=\"article-full-body sans-serif\"><strong>3. <\/strong>Photoshop\u2019s \u2018Clone Stamp Tool\u2019 or \u2018Spot Healing Brush Tool\u2019 can eliminate any large stars or halos that remain. <\/p>\n<\/div><\/section>\n\n<div class=\"no-tts wp-block-image article-in-image photo\"><figure class=\"no-tts alignleft is-resized\"><img loading=\"lazy\" src=\"https:\/\/dj9jqhxgw9833.cloudfront.net\/uploads\/sites\/77\/2022\/06\/a07743d0-ba9f-480b-8393-e7bb344e3da9.jpg\" alt=\"\" class=\"no-tts wp-image-32907\" width=\"79\" height=\"79\" srcset=\"https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/06\/a07743d0-ba9f-480b-8393-e7bb344e3da9.jpg 315w, https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/06\/a07743d0-ba9f-480b-8393-e7bb344e3da9-300x300.jpg 300w, https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/06\/a07743d0-ba9f-480b-8393-e7bb344e3da9-150x150.jpg 150w\" sizes=\"(max-width: 79px) 100vw, 79px\" \/><figcaption> <\/figcaption><\/figure><\/div>\n\n<p>Warren Keller is an astrophotographer and image-processing educator. See www.mastersofpixinsight.com<\/p>\n\n<p><\/p>\n\n<p><\/p>\n\n<p class=\"footer\">ALL PHOTOS: WARREN KELLER <\/p>\n","protected":false},"excerpt":{"rendered":"<p>Photograph the Milky Way<\/p>\n","protected":false},"author":24,"featured_media":32901,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"ub_ctt_via":"","purple_page_number":"78","purple_custom_meta_purple_page_number":"78","purple_seq_number":"1","purple_custom_meta_purple_seq_number":"1","purple_source_article":"article_78-1.xml","purple_custom_meta_purple_source_article":"article_78-1.xml","purple_source_issue":"July-2022","purple_custom_meta_purple_source_issue":"July-2022","purple_external_id":"July-2022-78-1","purple_custom_meta_purple_external_id":"July-2022-78-1","purple_issue_code":"|0000086554||","purple_custom_meta_purple_issue_code":"|0000086554||","purple_android_product":"com.im.skyatnight.206","purple_custom_meta_purple_android_product":"2022skyatnightJuly","purple_ios_product":"com.im.skyatnight.206","purple_custom_meta_purple_ios_product":"2022skyatnightJuly","purple_web_product":"","purple_custom_meta_purple_web_product":"","purple_publication_id":"075fab74-0a21-4201-866a-899d6c41c40c","purple_migrated":"","kt_blocks_editor_width":""},"categories":[34],"tags":[14],"featured_image_src":"https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/06\/97a2eb77-aac6-4629-8c3a-deb214a04025.jpg","author_info":{"display_name":"importmanagerhub@sprylab.com","author_link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/author\/importmanagerhubsprylab-com\/"},"acf":{"readingTimeMinutes":"5","apple_news_title":""},"uagb_featured_image_src":{"full":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/06\/97a2eb77-aac6-4629-8c3a-deb214a04025.jpg",1216,944,false],"thumbnail":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/06\/97a2eb77-aac6-4629-8c3a-deb214a04025-150x150.jpg",150,150,true],"medium":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/06\/97a2eb77-aac6-4629-8c3a-deb214a04025-300x233.jpg",300,233,true],"medium_large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/06\/97a2eb77-aac6-4629-8c3a-deb214a04025-768x596.jpg",768,596,true],"large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/06\/97a2eb77-aac6-4629-8c3a-deb214a04025-1024x795.jpg",800,621,true],"1536x1536":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/06\/97a2eb77-aac6-4629-8c3a-deb214a04025.jpg",1216,944,false],"2048x2048":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/06\/97a2eb77-aac6-4629-8c3a-deb214a04025.jpg",1216,944,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":"Photograph the Milky Way","_links":{"self":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/posts\/32908"}],"collection":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/users\/24"}],"replies":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/comments?post=32908"}],"version-history":[{"count":9,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/posts\/32908\/revisions"}],"predecessor-version":[{"id":33423,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/posts\/32908\/revisions\/33423"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/media\/32901"}],"wp:attachment":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/media?parent=32908"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/categories?post=32908"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/tags?post=32908"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}