Trick Photoshop

Suppose you have a dark image, you can change the tone with Levels in Photoshop, but you can do it another way too. Similalry, if you have an image which is light in tone, you can always darken it. 

Here is a free stock photo. It belongs to *FullBodyShotsHelping manipulators everywhere

The image has dark tones and may be purposefully so.

 Step 1 : Go to the Channels palette.

Step 2 : Rotate through the Red, Green and Blue channels. See which is the lightest. Here the Red channel is the lightest.

 Step 3 : Press CTRL+A (Select All), then press CTRL+C (Copy).

Step 4 : Click on the RGB channel.

 Step 5 : Go over to the Layers palette.

 Step 6 : Press CTRL+V (Paste). The selection is pasted into a new Layer1.

 Step 7 : Click on the Blend Modes and change it to Screen from Normal.

 And here is the effect that I wanted. It works all the time and is very simple to do.

 Step 8 : You can lower the Opacity a tad. I have reduced it to 90%. This is optional.

 This is how the image looks after lowering the Opacity to 90%.

 Now let us take an image like this, where there is excess of light. This is a free stock image. It belongs to =Falln-Stock