Tutorial 3: How to darken the background

This Tutorial shows 3 different ways (Levels, Selective Color, Lighting Effects Filter) to darken the background of an image with Photoshop 7/CS.
It also briefly discusses how to use Blending Modes for layers and Layer Masks. Levels, Lighting Effects Filters and Blending also work for Photoshop Elements 3.

There are several other ways to darken backgrounds in Photoshop (Curves, ...) and many other image processing tools offer similar functionality to improve your photos.

Have fun - Sabine

Before	Before	Before

After: Levels	After: Selective Color	After: Lighting Effects Filter

Use the Levels tool to darken the background

When to use:	If you simply want to further darken already dark areas in your image. Remember that you will loose detail on the dark side, i.e. your main subject should be something light.
Photoshop Tool:	Layers menu: New Adjustment Layer: Levels
See also:	Some time ago i wrote a basic page about Levels and Levels Adjustment and a tutorial about Manual and Automatic Level Adjustment.
Image Info:	Risbecia pulchella on ugly sandy background (Kubu, East Bali)
EXIF Info:	Automatic with F11 at 1/100s, full zoom, internal strobe
Problem:	I wanted to generally darken the whole background.

Step 1: Create an adjustment layer for the Levels tool

It is important to use an adjustment layer to be able to fine tune the effect later on by changing opacity or using a blending mode. With Photoshop CS or 7 we can also use the layer mask to apply the effect to specific areas only. This is not possible with Photoshop Elements. To create the layer: In the layers palette, select the background layer. In the Layers menu choose New adjustment layer and select Levels as adjustment tool. The dialog to adjust Levels opens up. Simply click OK to create the adjustment level.
Your layers palette should look like this now: To reopen the Levels dialog, simply double cklick on the Levels icon (red arrow).

Step 2: Increasing the Input Levels Shadow Value with the Levels tool

Reopen the Levels tool and move the left slider under the Input Levels histogram to the right or change the value for Input Shadows to something greater than 0.
This darkens already dark areas in your image. If you move the slider completely to the right almost the whole image turns black.
My Input Shadow Value of 50 is enough to darken the gray sand without loosing too much detail on the nudibranch.

This is probably enough for a quick and easy fix.

Step 3: Use a layer mask to apply the adjustment (Photoshop 7/CS only).

Assuming that i wanted to further darken the background without loosing detail on the nudibranch or if the slug was a bit darker, i could use a layer mask to control the areas where the adjustment should be applied and mask areas that i want to preserve the way they are.
Photoshop 7/CS automatically creates an empty layer mask for each adjustment level.

To activate the layer mask for the adjustment level, simply click on it.
You can mask and unmask image areas by directly painting on the image with a tool of your choice, like the brush. Use Black to mask areas, White to unmask areas and different Greys to create more or less semi-transparent areas (to create smooth transitions).
The layer mask also has it's own channel, simply switch to channels and activate it there to see what is masked

In this version of the image i increased the Input Shadow Value to 75 to better show the effect of the layer mask. Then i activated the mask and carefully painted Black and Gray on the image. here the layer mask is not completed to show the difference between masked and unmasked areas.

Photoshop Element does not support layer masks but you can help yourself by selecting the area to darken (or to keep, depending on what is easier to select), copy your selection to a new layer (Ctrl C, Ctrl V will create a new layer with your selection) and create the adjustment layer for levels on top of the image layer to adjust.

Step 4: Finetuning the Layer Mask

The best way to control your layer mask is to switch from the levels to the channels tab. The Layer mask has it's own channel here. Simply select it and continue to paint on your image.
If you display (small eye left of the channel) the layer mask channel while the RGB channel is also displayed, you can see the mask on your image (default mask color is red). If you hide the RGB channel, you see the mask as you painted it in black, grey and white.

Here is the final result:

Using Selective Color to darken the background (Photoshop CS/7 only)

When to use:	If you need to control exactly which colors to darken and which to keep.
Photoshop Tool:	Layers menu: New Adjustment Layer: Selective Color
Image Info:	Black-spot Surgeonfish (Acanthurus bariene) portrait (Tulamben Wreck, East Bali)
EXIF Info:	Manual with F11 at 1/125s, focal length 8,2mm, external strobe with half power
Problem:	I wanted an almost black background for this fish portrait. I also assumed that after darkening the background, there would be less backscatter to remove.

Step 1: Create an adjustment layer for the Selective Color tool

It is important to use an adjustment layer to be able to use the layer mask to apply the effect to specific areas only.
To create the layer: In the layers palette, select the background layer. In the Layers menu choose New adjustment layer and select Selective Color as adjustment tool.
The dialog to adjust Colors opens up. Simply click OK to create the adjustment level.
To reopen the Selective Color dialog, simply double cklick on the Selective Color icon (as decribed for the levels tool in Step 1 of the previous example).

Step 2: Paint on the layer mask to protect the fish

Create the layer mask as described in Steps 3 and 4 of the previous examle.
You can even apply a Gaussian Blur (of ~ 5 pixels) to the mask to create a smooth transition from masked to unmasked areas.
The resulting mask should look like this (when viewed as channel):

Step 3: Adjust colors to darken the background.

Reopen the Selective Color tool and and select Absolute as Method for now.
The difference between Relative and Absolute is sometimes hard to see and sometimes stunning. Absolute increases or decreases the amount of the chosen color independent of how strong it's amount already is, whereas Relative takes the amount of already existing color into account. If you increase the amount of Black in Red by 100%, Absolute will do this evenly, no matter if it's light Red or dark Red, whereas Relative will add less Black to light Red and more Black to dark Red.
Without our layer mask, Relative would be the better method.

The easiest way to darken a color is to simply increase it's value for black.

In the Selective Color dialog, choose Black as color to adjust.

Increase Black in Black by 100%. Increasing Cyan in Black by 25% and decreasing Yellow in Black by 25% gives our black a nice bluish cast.

Now Choose Grey as color to adjust.
Increase Black in Grey by 100%. Increase Cyan in Grey by 10% and decrease Yellow in Grey by 10% to keep the bluish black background.

Finaly Choose Cyan as color to adjust (no picture) and Increase Black in Cyan by 100%.

Most of the backscatter in the background should be gone by now.

Here is the final result:

I used the clone tool on the original background (make sure to select it before cloning) to get rid of the last backscatter. Then i reduced all my layers to the background layer (Levels menu).

Simulating a strobe with the Lighting Effects Filter to darken the background

When to use:	If you want to highlight a specific area and darken it's surroundings.
Photoshop Tool:	Filter menu: Rendering Filters: Lighting Effects
Image Info:	Pom-Pom Frogfish (Antennarius hispidus sp.) camouflaged in a bed of algae (Secret Bay, West Bali)
EXIF Info:	Automatic with F11 at 1/30s, no zoom, internal strobe
Problem:	I wanted to darken the background on the left side to make the fish pop out a little bit more and get rid of the Anglerfish foot (there were several of them close together) in the top left corner. Using the clone tool to get rid of the other fish and Levels or Selective Color applied to a layer mask to manipulate specific areas of the image would have been other options but applying a simulated strobe was the easiest solution here.

Step 1: Duplicate the background layer

It is important to apply this filter to a copy of the background layer to be able to fine tune the effect later on by changing opacity or using a blending mode.
To create a copy: In the layers palette, select the background layer. Right click on it and choose duplicate layer from the popup menu or choose Duplicate layer from the Layers menu.

Step 2: Apply the Lighting Effects Filter

Select the copy of the background layer in the layers palette. Next choose Rendering Filters: Lighting Effects from the Filters menu.
Set the Style to Strobe and the Light Type to Spot. Adjust the color, center and direction of the light as well as the other properties as shown here to create the desired effect and keep in mind that the direction of the light should match the original strobe position.
(Sorry i had to english version of PS available. The Texture chanel must be set to None)

This looks rather unnatural, we'll have to tone down the effect

Step 3a: Change the layer opacity to tone down the effect.

Fortunately we applied the filter to a copy of our background layer, where we can simply decrease the Opacity to create a much more natural effect..
Select the copy of the background layer in the layers palette and change the value for opacity to ~30% (type in a new value, click into the value field and use the Up and Down arrows to change the value by one or Shift Up/Down to change the value by 10 or use the slider).

By clicking on the small eye symbol left of the layer you can switch the adjustment on and off.

This is better than the original, but i'm not yet really happy with it.

Step 3b: Use another blending mode

So far, we only used the normal blending mode for our layer with the strobe effect.
Photoshop offers a variety of different blending mode to create interesting and sometimes strange effects.
One of my varourite blending modes is Soft Light and i'll use it here to further darken the background.

Make sure that the copy of the background layer is selected in the layers palette.
Set the value for opacity back up to 100% to get a better idea of how different blending modes change your image.
The blending mode of each layer is by default set to Normal. Simply open the Choice list and select Soft Light as new blending mode (or play around with the other options).

With opacity set to 100% the blending effect is rather dramatic. Decrease the opacity until the effect is toned down to look natural (unless you want to create an artsy looking image).
I ended up with an opacity of 50%

Here is the final result:

Remember

Please don't forget to mention corrections and improvements when you publish your pictures ;-)


		Text and Photos: © Sabine Noack, January 2005.