{"id":25353,"date":"2021-10-21T00:00:00","date_gmt":"2021-10-21T00:00:00","guid":{"rendered":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/?post_type=purple_issue&p=25353"},"modified":"2021-10-21T12:32:45","modified_gmt":"2021-10-21T12:32:45","slug":"processing-using-a-histogram-to-improve-nebulae-images","status":"publish","type":"post","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/2021\/10\/21\/processing-using-a-histogram-to-improve-nebulae-images\/","title":{"rendered":"Processing: Using a histogram to improve nebulae images"},"content":{"rendered":"\n

Enrich a nebula\u2019s colours and add depth to the background with photo-editing software<\/p>\n\n

\"\"
After: following colour adjustments to the nebulae and background darkening, the image of the North America and Pelican Nebulae is transformed<\/figcaption><\/figure><\/div>\n\n
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Before: the original stacked nebulae image of 78 images is too green and lacks impact<\/figcaption><\/figure><\/div>\n\n

When you take an image with a camera, in a perfect world you would get every exposure spot-on, meaning there would be no need to make any further adjustments. But the reality is that we nearly always need to make adjustments after taking photographs, usually using our preferred photo-editing software. In most cases it\u2019s a matter of studying a histogram and using the \u2018Levels\u2019 and \u2018Curves\u2019 features or, in the case of PaintShop Pro, an actual \u2018Histogram adjustment\u2019 tool.<\/p>\n\n

The histogram itself is simply a way of showing the varying light levels captured in your image from the dark tones on the left (the \u2018Blacks\u2019) to the white highlights on the right (the \u2018Whites\u2019). A bump in the middle, representing the middle tones, can also be adjusted. The histogram can also be used for adjusting the individual \u2018Red\u2019, \u2018Green\u2019 and \u2018Blue\u2019 (RGB) colour levels in the same way, making it a very flexible and powerful tool in your photo-editing armoury.<\/p>\n\n

In this month\u2019s article we will look at how to use PaintShop Pro\u2019s \u2018Histogram adjustment\u2019 tool to improve the colours in a nebulae image. As an example, we are using an already stacked image of the North America and Pelican Nebulae (above).<\/span><\/p>\n\n

Start on green<\/strong><\/h5>\n\n

The stack of 78 images was taken with a modified Canon 300D DSLR camera through a telescope. As the resulting stack is a little green and lacklustre, the first action in PaintShop Pro is to select and click the following from the top menu: \u2018Adjust > Brightness and Contrast > Histogram adjustment\u2019. This brings up the \u2018Histogram adjustment\u2019 box (as shown on the right-hand side in Screenshot 1). There are plenty of options here, so first ensure you tick the \u2018Preview on image\u2019 so you can see any changes taking place live on the screen. For now, the rest of the options can be left as they are, but the first job is to deal with the greenish tinge.<\/p>\n\n

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Screenshot 1: Locate the \u2018Histogram adjustment\u2019 box in PaintShop Pro<\/figcaption><\/figure><\/div>\n\n
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Screenshot 2: Tweak the green in the image by clicking \u2018Colours > Green\u2019\u2026<\/figcaption><\/figure><\/div>\n\n

To do this select \u2018Colours\u2019 and then \u2018Green\u2019 from the drop-down list in \u2018Histogram adjustment\u2019 box (See Screenshot 2). This shows the histogram for the green part of the image, so now use your mouse to click and hold the left-hand black adjustment handle at the base of the histogram and carefully slide it to the right until it\u2019s close to the start of the green section. The green is now darkened, removing the cast, but it\u2019s showing up some blue in the image that you<\/span> might not want. To deal with this, keep the \u2018Histogram adjustment\u2019 box open and repeat the steps for the \u2018Green\u2019 adjustments, but instead choose \u2018Blue\u2019 from the drop-down list and adjust it slightly (See Screenshot 3). In both the \u2018Green\u2019 and \u2018Blue\u2019 sections, make subtle adjustments until you\u2019re happy with the result and then click \u2018OK\u2019 at the bottom of the box to apply them to the image.<\/p>\n\n

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Screenshot 3: \u2026and then select \u2018Blue\u2019 to remove any unwanted blue cast\u2026<\/figcaption><\/figure><\/div>\n\n
Remember to reset<\/strong><\/h5>\n\n

If the image still looks a little dim, you can adjust it by re-opening the \u2018Histogram adjustment\u2019 box. If the \u2018Settings\u2019 menu says \u2018Last used\u2019 then press the \u2018Reset to default\u2019 to the far right of the box, otherwise the last set of adjustments will be applied again, and you don\u2019t want that. The \u2018Reset to default\u2019 sets the \u2018Histogram adjustment\u2019 function to the default of \u2018Luminance\u2019, which allows you to adjust the black adjustment handle at the left and slide it slightly to the right. Again, do this in small increments and watch carefully how the image changes until you\u2019re happy with the result. Although this has darkened the image slightly, you can amend this by moving the middle \u2018Gamma\u2019 adjuster a little to the right to change the curve of the histogram. Again, do this in small adjustments until you\u2019re happy with the result.<\/p>\n\n

At this stage you haven\u2019t needed to move the white adjustment handle for this particular image, but it may benefit from a slight adjustment. Remember, it is down to personal taste how much you push the adjustments. When you\u2019re happy, click \u2018OK\u2019 to finish the \u2018Luminance\u2019 adjustment.<\/span><\/p>\n\n

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Screenshot 4: \u2026and \u2018Red\u2019 to boost the hydrogen-alpha colours<\/figcaption><\/figure><\/div>\n\n

The image has been improved, but if you\u2019d like the nebulae to be a little redder, you can now open the \u2018Histogram adjustment\u2019 box again and click \u2018Select > Colours > Red\u2019 (See Screenshot 4). This time, move the white adjustment handle inwards a little at a time, watching how the image changes. Once you\u2019re satisfied, click \u2018OK\u2019 to close the box.<\/p>\n\n

These simple steps have removed the green and slight blue cast, darkened the background to a more natural view of space and brought out the hydrogenalpha (Ha) red emission of the nebulae, all by using one tool to make multiple small adjustments. The image can be further processed, if necessary, using the \u2018Saturation\u2019 tool but, for now you can enjoy the final, processed image of the North America and Pelican Nebulae (see main picture).<\/p>\n\n

<\/div>
\n

3 QUICK TIPS<\/h4>\n\n\n\n

1. <\/strong>Always make a series of small adjustments rather than one big one.<\/p>\n\n\n\n

2. <\/strong>Make sure the settings tab is either empty or press the \u2018Reset to default\u2019 button.<\/p>\n\n\n\n

3. <\/strong>Don\u2019t be afraid to explore the other options in the \u2018Histogram adjustments\u2019 box to further enhance your image.<\/p>\n<\/div><\/section>\n\n

\n
\n
\"\"<\/figure><\/div>\n<\/div>\n\n\n\n
\n

Paul Money is an astronomy writer and broadcaster, and is reviews editor for BBC Sky at Night Magazine<\/em><\/p>\n<\/div>\n<\/div>\n\n

ALL PICTURES: PAUL MONEY<\/p>\n","protected":false},"excerpt":{"rendered":"

Enrich a nebula\u2019s colours and add depth to the background with photo-editing software<\/p>\n","protected":false},"author":24,"featured_media":25345,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"ub_ctt_via":"","purple_page_number":"80","purple_custom_meta_purple_page_number":"80","purple_seq_number":"1","purple_custom_meta_purple_seq_number":"1","purple_source_article":"article_80-1.xml","purple_custom_meta_purple_source_article":"article_80-1.xml","purple_source_issue":"November-2021","purple_custom_meta_purple_source_issue":"November-2021","purple_external_id":"November-2021-80-1","purple_custom_meta_purple_external_id":"November-2021-80-1","purple_issue_code":"|0000086546||","purple_custom_meta_purple_issue_code":"|0000086546||","purple_android_product":"com.im.skyatnight.198","purple_custom_meta_purple_android_product":"com.im.skyatnight.198","purple_ios_product":"com.im.skyatnight.198","purple_custom_meta_purple_ios_product":"com.im.skyatnight.198","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\/2021\/10\/ada84a25-de6b-4149-8fb7-5171e2a7d8c6.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\/2021\/10\/ada84a25-de6b-4149-8fb7-5171e2a7d8c6.jpg",1397,951,false],"thumbnail":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2021\/10\/ada84a25-de6b-4149-8fb7-5171e2a7d8c6-150x150.jpg",150,150,true],"medium":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2021\/10\/ada84a25-de6b-4149-8fb7-5171e2a7d8c6-300x204.jpg",300,204,true],"medium_large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2021\/10\/ada84a25-de6b-4149-8fb7-5171e2a7d8c6-768x523.jpg",768,523,true],"large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2021\/10\/ada84a25-de6b-4149-8fb7-5171e2a7d8c6-1024x697.jpg",800,545,true],"1536x1536":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2021\/10\/ada84a25-de6b-4149-8fb7-5171e2a7d8c6.jpg",1397,951,false],"2048x2048":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2021\/10\/ada84a25-de6b-4149-8fb7-5171e2a7d8c6.jpg",1397,951,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":"Enrich a nebula\u2019s colours and add depth to the background with photo-editing software","_links":{"self":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/posts\/25353"}],"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=25353"}],"version-history":[{"count":8,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/posts\/25353\/revisions"}],"predecessor-version":[{"id":25907,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/posts\/25353\/revisions\/25907"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/media\/25345"}],"wp:attachment":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/media?parent=25353"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/categories?post=25353"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/tags?post=25353"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}