Selecting image luminosity
Video: Selecting image luminosityWith just one click, you can make a selection based on the tonal value or the luminosity of pixels in an image. This opens up all kinds of creative possibilities. In this movie, I'll show you how quick and easy it is to make an image luminosity selection and I'll give you one example of something creative you can do with that selection which is to create a split toned image. To make a selection based on the luminosity of the tonal values in the image, I'm going to go to the Channels panel. There in the Channels panel, you can see the Red, Green and Blue color channels that make up the color image as well as a Composite RGB Channel.
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Choosing the right selection tools for the job and using those tools effectively are among the most important skills for Photoshop users. In Photoshop CS4: Selections in Depth, Jan Kabili goes deep into the subject, showing the best practices for making and working with selections. Jan walks through the manual and automatic selection methods in Photoshop and offers pointers on choosing the most effective selection methods for an image. She explains the underlying relationship between selections and alpha channels, and shows how to fine-tune selections to get the desired results. Exercise files accompany the course.
- Selecting manually with the Marquee, Lasso, and Pen tools
- Saving time with automatic selection methods like the Quick Selection tool and the Magic Wand tool
- Fine-tuning selections with Refine Edge
- Working with selections in Quick Mask mode
- Moving, modifying, and combining selections
- Saving selections as alpha channels
- Making complex selections from color channels
- Using the Background Eraser tool to replace a background
- Installing and using the legacy Extract plug-in to isolate an object from its background
Selecting image luminosity
With just one click, you can make a selection based on the tonal value or the luminosity of pixels in an image. This opens up all kinds of creative possibilities. In this movie, I'll show you how quick and easy it is to make an image luminosity selection and I'll give you one example of something creative you can do with that selection which is to create a split toned image. To make a selection based on the luminosity of the tonal values in the image, I'm going to go to the Channels panel. There in the Channels panel, you can see the Red, Green and Blue color channels that make up the color image as well as a Composite RGB Channel.
The way to load image luminosity as a selection is to hold down the Command key on the Mac or the Ctrl key on the PC. And click on the thumbnail on that RGB Channel. This creates a selection with the brightest areas fully selected and the less bright areas partially selected according to their brightness. It's hard to visualize that in this marching ants view of the selection. I am going to show you this selection as a grayscale mask in an Alpha channel, which as you know from other movies in this course is just another way to represent a selection.
To create an Alpha channel from this selection, I'll go to the bottom of the Channels panel and I click this icon which saves the selection as a channel. Then I'm going to deselect by pressing Command +D on the Mac or Ctrl+D on the PC, and I'm going to click on that Alpha Channel to display it here in the document window. It looks almost like a black and white photograph. Doesn't it? What it really is, is a representation of the selection with the fully selected pixels in white, the fully non- selected pixels in black, and the partially selected pixels in all of the shades of gray and between.
Now that you have had a chance to see this visual representation of an image luminosity selection, I'm going to delete this Alpha channel because it's really not necessary for the rest of the exercise. So I'll click on it in the Channels panel and drag it to the Trashcan. So what can you do with the selection based on image luminosity? There are lots of things. Once you've got the highlight areas selected, you might brighten them to increase contrast. You might invert your selections so that you have the shadow areas selected, and darken those. What I'm going to do is tone the highlight areas in gold and then tone the shadow areas in a dark purple blue to create what's known as a split toned image.
Simulating the kind of split toning that you can do with a lot more time and some chemicals in the traditional dark room. The first step in making a split toned image is to convert a color image to black and white. To do that, I'm going to click on the Layers panel. There is a single layer in the file which I do have selected and so I'm going to convert that to black and white by going up to the Image menu, choosing Adjustments and choosing Black & White. I'm going to accept all of the black and white settings and just click OK.
Now I'm going to go back to the Channels panel because I want you to see that this is still a Red, Green, Blue color mode image. I had basically just taken the color out and I'm left with the same tonal values that were underlying the image when you saw it in color a few moments ago. Because these tonal values are the same, I can load them again as a selection by going to the RGB Composite Channel, and again holding down the Command key on a Mac or the Ctrl key on a PC and clicking on the thumbnail on the RGB Channel.
So now I have the highlight selected in the image and I would like to tone them a gold color. I'll go back to the Layers panel and then I'm going to go to the bottom of the Layers panel and click this icon, the Black & White circle to create a new fill layer. This menu lists all of the adjustment layers and at the top, it lists three flavors of fill layer. I'm going to choose Solid Color. That opens the Color Picker where you can choose a color for tinting the highlights. I'm going to use this gold color and I'll click OK.
Now all of the highlights in the image are tinted gold. And there is a mask that automatically comes with every fill layer that is protecting the non-selected areas, the dark areas here from that gold tint. Displaying the gold tint on the brightest areas and partially displaying the gold tint on the gray areas in between. Next, I would like to add a tint to the shadows in this image. I'm going to bring back my selection of the highlights by going to the Select menu and choosing Reselect.
And then I'm going to invert that selection so the shadow areas are selected rather than the highlights. So I'll go to the Select menu and I'll go to Inverse. Now with the shadow areas selected, I'm going to add another fill layer by going to the bottom of the Layers panel, clicking that Black & White circle icon and choosing Solid Color again. In the Color Picker that opens, I'll use the slider in the middle to move to the blue purple range, somewhere around there and I want a very dark purple, something like that. I'll click OK.
And now I have another color fill layer with its own layer mask based on the inverted image luminosity selection and the purple color is tinting all of the dark areas of the image, the lighter areas are protected from this tint. I think this tint is actually a little bit too strong, so I'm going to reduce the opacity of the purple color fill layer by making sure I have that layer selected in the Layers panel and then going to the Opacity slider at the top of the Layers panel, moving my mouse over the Opacity label and dragging to the left and maybe I'll put this at about 50%.
So I have managed to use that image luminosity selection that was so quick and easy to make by clicking on the thumbnail on the RGB Channel. As the basis for double tinting this image, tinting the highlights gold and the shadows dark blue. This is just one of the creative possibilities that you have when you make a selection based on image luminosity. As you can see, making a selection like this is a really powerful feature but it's one that's sometimes overlooked, and I urge you to keep it in mind as you are working on your own images.
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