{"id":4162,"date":"2018-11-04T14:20:26","date_gmt":"2018-11-04T14:20:26","guid":{"rendered":"http:\/\/dunchurchps.com\/dps-wp\/?page_id=4162"},"modified":"2018-11-05T09:54:11","modified_gmt":"2018-11-05T09:54:11","slug":"luminosity-masks","status":"publish","type":"page","link":"https:\/\/dunchurchps.com\/dps-wp\/luminosity-masks\/","title":{"rendered":"Luminosity Masks"},"content":{"rendered":"

Illuminating Luminosity Masks\u00a0<\/strong>\u00a0(Author: Eric Tatham)<\/em><\/p>\n

As an example, here\u2019s an image in which I want to lighten the foreground to bring out some shadow detail but do not want to blow out the highlights in the sun and sky. (See Fig 1)<\/p>\n

\"\"(Fig 1 – The original image)<\/em><\/p>\n

I could use the Burn Tool<\/strong> in Photoshop but I would have to be quite careful to only brush over the regions I want to affect.<\/p>\n

In this particular image there is quite straightforward separation between the darker foreground and the lighter background so I could simply select the foreground and create a mask to protect the background.<\/p>\n

Masking images according to lightness and darkness is known as luminance<\/em><\/strong> or luminosity masking<\/em><\/strong>.<\/p>\n

For our purposes we can think of luminance as being equivalent to brightness. If you convert any colour image to black and white the resulting greys represent luminance values; the lighter areas having a higher luminance values. (See Fig 2)<\/p>\n

\"\"(Fig 2 – Original image converted to Black and\u00a0White to show luminance levels)<\/i><\/p>\n

The separation between light and dark areas of an image may not be as clear-cut as in our sample photograph and such a mask would be hard to produce by hand. Fortunately we can use Photoshop to help us create a much more accurate mask.<\/p>\n

Here\u2019s how.<\/p>\n

Use Cmd-J<\/strong> on a Mac (or Ctrl-J<\/strong> in Windows) to create a copy of your image.<\/p>\n

\"\"<\/p>\n

(Fig 3 – Copy layer)<\/em><\/p>\n

Switch from the Layers<\/strong> Panel<\/strong> to the Channels<\/strong>.<\/p>\n

Hold the cursor over the RGB <\/strong>Channel and left-click whilst holding down the Cmd<\/strong> key on a Mac (Ctrl<\/strong> key in Windows).<\/p>\n

Marching ants should appear on your image showing the regions selected. This region will include all pixels that have a luminance value of greater than 50%. (See Fig 4)<\/p>\n

\"\" (Fig 4 – Highlight selection)<\/em><\/p>\n

Go back to the Layers<\/strong>\u00a0panel and select your image layer. Right-click on the Create New Fill or Adjustment Layer <\/strong>icon and select Curves<\/strong> from the drop-down list. (See Figs 5 and 6)<\/p>\n

\"\"<\/p>\n

(Fig 5 – Create new adjustment layer)<\/em><\/p>\n

\"\"<\/p>\n

(Fig 6 – Create new Curves adjustment layer)<\/em><\/p>\n

This will create a Curves Adjustment Layer<\/strong> with a mask that protects the pixels that have a luminance level darker than 50%. (See Fig 7)<\/p>\n

\"\"<\/p>\n

(Fig 7 – Luminosity mask for highlights)<\/em><\/p>\n

The mask effectively divides the image into two regions. One containing all pixels with less than 50% luminance and the other with 50% luminance or more.<\/p>\n

Remember the Black areas of the mask protect the underlying image layers and White areas are transparent.<\/p>\n

You can view the mask by selecting it in the Layers<\/strong> panel then clicking whilst holding down the Alt<\/strong> key on a Mac (or the Option<\/strong>\u00a0key with Windows). (See Fig 8)<\/p>\n

\"\"<\/p>\n

(Fig 8 – Luminosity mask for highlights)<\/em><\/p>\n

Once again, click with Alt<\/strong> or Option<\/strong> held down to change back to the main image.<\/p>\n

Now if we manipulate our adjustment\u00a0Curve<\/strong> only the lighter areas of the image are affected. (See Fig 9)<\/p>\n

\"\"<\/p>\n

(Fig 9 – Curve adjustment for highlights)<\/em><\/p>\n

For this particular image it was actually the darker areas that we wanted to adjust so to do this we need to Invert<\/strong> the mask.<\/p>\n

We can quickly invert by selecting the mask in the Layers<\/strong> panel then pressing Cmd-i<\/strong> on a Mac (or Ctrl-i<\/strong> with Windows).<\/p>\n

The mask now protects the lightest parts of the image and allows us to adjust the Curve<\/strong> for the dark areas. (See Figs 10, 11 and 12)<\/p>\n

\"\"<\/p>\n

(Fig 10 – Luminosity mask for shadows)<\/em><\/p>\n

\"\"<\/p>\n

(Fig 11 – Luminosity mask for shadows)<\/em><\/p>\n

\"\"<\/p>\n

(Fig 12 – Curve adjustment affecting only the shadows)<\/em><\/p>\n

It is possible to take the highlight and shadow masks we have produced and from them create additional masks that further sub-divide the highlight regions and the shadows. In this way we can create a whole stack of luminosity masks<\/strong> that will allow us to selectively adjust more refined ranges of luminance.<\/p>\n

 <\/p>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

Illuminating Luminosity Masks\u00a0\u00a0(Author: Eric Tatham) As an example, here\u2019s an image in which I want to lighten the foreground to bring out some shadow detail but do not want to […]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"open","ping_status":"closed","template":"","meta":{"_eb_attr":"","_templately_pack_id":"","_templately_imported_at":"","_templately_source":"","_templately_import_session_id":"","footnotes":""},"class_list":["post-4162","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/dunchurchps.com\/dps-wp\/wp-json\/wp\/v2\/pages\/4162","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/dunchurchps.com\/dps-wp\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/dunchurchps.com\/dps-wp\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/dunchurchps.com\/dps-wp\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/dunchurchps.com\/dps-wp\/wp-json\/wp\/v2\/comments?post=4162"}],"version-history":[{"count":5,"href":"https:\/\/dunchurchps.com\/dps-wp\/wp-json\/wp\/v2\/pages\/4162\/revisions"}],"predecessor-version":[{"id":4182,"href":"https:\/\/dunchurchps.com\/dps-wp\/wp-json\/wp\/v2\/pages\/4162\/revisions\/4182"}],"wp:attachment":[{"href":"https:\/\/dunchurchps.com\/dps-wp\/wp-json\/wp\/v2\/media?parent=4162"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}