By Jim Pickrell.
This section covers three commonly used Blending Modes - Multiply, Screen, and Overlay. These three Blending Modes are used frequently by photographers for image processing.
Nikolai has already discussed the Normal Blending Mode, as well as Dissolve, Difference and Exclusion. Therefore, the reader is expected to know, and understand, the basics of creating a duplicate layer with the command CTRL-J ( Apple-J on the MAC) to create a copy of the background layer in the Layers Palette. This is done when using the Multiply or Screen Blending Modes.
The reader is also assumed to know how to use the Opacity Slider in the Layers Palette to modify the intensity of the Blend Mode being used.
The Overlay Blending Mode may be performed with a new solid color layer of medium gray, or may simply be brushed onto the image with the Brush Tool.
Here is an image of a white barn that looks a little too bright. We can darken it with the Multiply Blending Mode.
The Help section in PSCS 2 says about Multiply Blending "Multiply looks at the color information in each channel and multiplies the base color by the blend color. The result color is ALWAYS a darker color. Multiplying any color with black produces black. Multiplying any color with white leaves the color unchanged. When youre painting with a color other than black or white, successive strokes with a painting tool produce progressively darker colors. The effect is similar to drawing on the image with multiple marking pens."
Martin Evening in his "Adobe Photoshop CS2 for Photographers" says "the Multiply Blending Mode Multiplies the base by the blend pixel, except where the blend color is white" So what are these paragraphs really saying?? The darker the pixel in the top layer, which is multiplied by the base pixel beneath it, the darker the resultant final pixel. Black in the upper layer (blend) give the darkest pixel, and white (upper layer ) causes no effect.
So, with Multiply Blending, we CAN darken a moderately over exposed image.
If you open an image and duplicate it on the Layers Palette with a CTRL-J ( or Apple-J on the MAC) and then use the Multipy Blending Mode, the result is a significantly darker image overall, similar to sandwiching two Kodachromes together in a slide projector. The Opacity slider can then be used to diminish the effect from 100% down to a not discernible 1%.
Duplicate the barn image with CTRL-J(Apple -J) and you will have two layers, the background and the upper layer. If these are then Multiply Blended, they will become significantly darker.
Here is the barn image after being duplicated in the Layers Palette and then applying the Multiply Blending Mode at 100% (If the effect is not strong enough, just hit CTRL-J a second time for an additional blending layer and see the effect grow right before your eyes.)
Of course, as Nik demonstrated so well, masks can be used to limit the effects of the blending modes, and that is also true with the Multiply blending mode. Blending Modes are not limited to the RGB channels either. You can convert the image to LAB, and then use the Blend IF commands to limit the Multiply Blending Mode to just a limited portion of the Lightness or the A or B channels. This can be used to darken a sky without doing any selections first, just letting the color of the sky act directly through the B channel to limit the effect to the blue pixels only.
Here the image was duplicated with CTRL-J and the switched to LAB. In the Layers Palette, the Blend If command was selected from the drop down menu elicited by the Blending Options button in the upper right of the Layers Palette.
The Blending Options dialogue box looks like this.
This Blending Options box is for blending in the Normal Mode, but another selection offered by the Blend Mode box will be Multiply Blending.
This Blending Options box is being used with an image in the LAB color space, as the Lightness channel is selected in the lowest box. This could be changed to the A or B channel also. If the B channel is selected the effect can be limited to the yellow or blue portions of the base image, or some combination of the two by the sliders below the Blend If box.
By moving the image to the LAB color space, and Multiply Blending limited to the blue half of the the B channel, skies that are too thin can be nicely thickened as seen in the last barn image above.
This can be far more precise than trying to do a selection, then feathering it to hide the selection.
Multiply Blending can also be done on the Lightness Channel to darken it and increase its contrast.
The Multiply Blend can also be performed on a single layer of an image with the Brush Tool set to Multiply mode with Black ink, and a light opacity ~ 10-20% with a very soft feathery brush.
Screen Blending is almost exactly the opposite of Multiply Blending. Photoshop CS2 Help command says "Screen Looks at each channels color information and multiplies the inverse of the blend and base colors. The resultant color is always a lighter color. Screening with black leaves the color unchanged. Screening with white produces white. The effect is similar to projecting multiple photographic slides on top of each other."
Martin Evening in his book says that "Screen mode multiplies the Inverse of the Blend and the Base pixels, always making a lighter color, except where the blend color is black".
The effect is to lighten an underexposed, too dark image.
Again create a copy of the background layer with CTRL-J(Apple -J or Command-J on the MAC ) and then use Screen Mode to lighten the image. A Mask ( like the luminosity channel inverted ) can be used to help limit the effects only to the darker values.
Here is an image of a wasp that is too dark. ( I picked this image because it could be lighter )
Here we see the very average green frog that could use a bit of pop.
Which brings us to the Overlay Blend Mode, which Photoshop PSCS2 says "Overlay Multiplies or Screens the colors, depending on the base color. Patterns or colors overlay the existing pixels while preserving the highlights and shadows of the base color. The base color is not replaced but is mixed with the blend color to reflect the lightness or darkness of the original color."
Author Martin Evening says Overlay "superimposes the blend image on the base ( multiplying OR screening the colors depending on the base color) whilst preserving the highlights and shadows. Blending with 50% gray ( neutral gray) has no effect"
Now this description is not intuitively obvious to me at all!!
There is an easier way to think of, and use Overlay Blending. It does not require two layers, but just uses the Brush Tool in the Overlay Blending Mode, which is how I usually use the Overlay Blending Mode. If the Brush is set to use Black ink, then it will act like Burning an image in an enlarger in the darkroom. Darks will get darker with more contrast. If the Brush tool is used with White ink, the result will be to dodge the light beam to the print in the enlarger and will make the image lighter with higher contrast.
So set the ink for the Brush tool to black and the opacity to maybe 15-20% and use a soft, featherd brush to begin painting in some darker, deeper tones with more contrast. Or switch the ink to white in the Brush tools ( hit the D Key for the default ink colors and the X key to switch from black to white ), set the opacity to 10% or so, and begin to paint on the image to lighten selected areas with the Brush tool in the Overlay Mode. This is the way I most frequently use the Overlay Blend Mode - to replace the dodging and burning tools which seem rather crude by comparison.
My preferred way is to use the Overlay Blend Mode with the Brush Tool on a duplicate of the base image in an adjustment layer. That allows me to alter the image editing, and then finally tune the amount via the Opacity Slider.
Here is the frog with the chest lighted by painting with the Brush Tool with White ink in the Overlay Blending Mode with an opacity of 20% and darkening the skin and dark green areas by using the Brush in Overlay Blending Mode with Black ink at 20% opacity.
The nice aspect of doing it this way is that no selections were necessary, I could just watch the image as I worked. If I got too much darkening outside the frogs legs, a very brief touch up with the history brush quickly brushed the mistake away.
I was introduced to using Overlay Blending as an improvement to the Dodge and Burn Tools, by Cletus, 2 years ago here on Digital Grin.
His post said "Ditch the burn tool!"
He said "There is a pretty cool way to get the same effect as the dodge/burn tools in an pseudo adjustment layer:
1. Alt + click (Mac: Option+click) on the new layer button in the layers palette.
2. In the New Layer dialog, change the mode of the new layer to Overlay
3. Make sure that Fill with Overlay-neutral color is checked
4. Click OK You've just added a new layer filled with 50% gray. In overlay mode 50% gray has no effect. So how do you use this new layer???
1. Set your foreground color to black (actually any shade of gray darker than 50% will work)
2. Grab the paintbrush (use a fairly large soft-edged
brush) 3. Set the paintbrush opacity (and/or flow) in the 20-50% range
4. Start painting on your new layer
Any areas on the layer that are darker than 50% gray will darken the underlying image (burning). Guess what happens if your foreground color is white (or a shade of gray lighter than 50%)??? You start to lighten the underlying image (dodging). If you dodge or burn an area and you don't like the result? Set your foreground color to 50% gray and paint over the area. The dodge/burn effect will be wiped away!
Because you're doing the dodge/burn with a layer, you can do all kinds of cool stuff:
Use selections to dodge/burn areas of an image (select the area then fill it with an appropriate shade of gray)
Use paths to dodge/burn areas
Use adjustment layers to control the amount of dodge/burn the layer gives
Run filters on your dodge/burn effect (I'm not quite sure why you would want to, but hey, as with anything in photoshop, at some point someone is going to find an application for it)"
Cletus has us add a new layer over the existing background layer, and fill it with neutral 50% gray. This can be gotten from the Color Picker or just selected as an option when Overlay Blend mode is selected. Then, using a brush with Black or White ink, the base image can be lightened or darkened. This allows you to return and change the edit later, without any destructive effects to the base image.
I just find it easier to just create a duplicate layer with CTRL-J and then use the Brush tool directly on the duplicate image in the Overlay Mode with black or white ink as called for and lighten or darken to taste.
In summary, I have discussed some of the uses of the Multiply, Screen and Overlay Blending Modes for Image editing.
You can discuss or ask questions about this tutorial on Digital Grin.