Photographers are not infallible. In spite of having advanced exposure metering systems, we sometimes do mess up the exposures. In some cases, the subject’s contrast and dynamic range may be greater than what the sensor was capable of recording.
In other cases, it could be human error. Whatever be the reason, we often land up with images that are underexposed, overexposed, or having too high or too low contrast. Very often, such pictures are confined to the trash can. But why do that when we can easily salvage them?
Our good old friend – Photoshop – allows us to correct certain errors. And of course, there are several ways to do the same thing in Photoshop. In this article, we shall learn the use of ‘Multiply’ and ‘Screen’ blending modes, along with some simple techniques that will further improve our pictures.
‘Screen’ Blending Mode
The Screen blending mode allows us to easily lighten an underexposed (dark) image.
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We have here a stock photograph of a city skyline taken after dusk but before the sky turned too dark. While the lights within the buildings seem reasonably well exposed, the dark areas are a bit too dark. Let’s try to balance the contrast.
1. Open the image in Photoshop. Ensure that the Layers palette is open (F7 key on the keyboard). I am using Photoshop CS3.
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2. It is important not to directly edit the pixels on the original image (that would be ‘destructive editing’). Hence always make a copy of the Background layer. You do that by dragging the Background layer to the ‘Create a new layer’ icon at the bottom of the Layers palette(Screen 1).
3. Now go to the Blending mode and select ‘Screen’ (click on the small downward pointing arrow where it says Normal and then click Screen in the drop-down menu, Screen 2). The entire picture will lighten(Screen 3). If you feel that the picture has become too light, you can control the lightness by using the Opacity control (Screen 4).
4. If you want to further lighten the image, drag the Background copy once more to the ‘Create a new layer’ icon at the bottom of the Layers palette (which will create Background copy 2).
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5. Now let’s take a look at our lightened copy (that is, Screen 3). Let’s say you like the lightening of the water but dislike the lightening of the sky. You would like the sky to be back to the original tone (or may be a tone that is in-between the original and the lightened tone). If that is the case, here is what you should do:
6. Whilst keeping Alt key pressed, click on ‘Add layer mask’ icon at the bottom of the layers palette (the icon with the circle in a square). This will add a black mask which will hide the entire effect of the Screen blending mode.
7. Now select the Brush tool (B) with somewhat medium hardness, and using white as the foreground color (at the lower end of the toolbox, the white square should be at the front. If not, just click the double-sided arrow next to the squares which says ‘Switch Foreground and Background Colors’), simply paint over the darker water and the buildings. If needed, you can also control the effect of the Brush tool by controlling the Opacity from the top of the screen. If you observe the black mask, the white area within the mask shows the area where you have cut a hole in the mask, thus reveling the tones below.
TIP: When painting on the buildings, you could inadvertently paint outside the required area. If that happens, just press the ‘X’ key on the keyboard and re-paint the affected area. It will also help if you enlarge the image to 100 percent before doing any intricate work on a small area.
8. Save your image using the Save As command. I have added a thin white frame around the image to confine the viewer’s attention to stay within the image.
Contd. on next page
‘Multiply’ Blending Mode
The Multiply blending mode allows us to easily darken an overexposed (light) image.
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This time we have a landscape that is too light in tone except for the rocks at the left and the foreground. Let’s try to balance the tones and the contrast.
1. Open the image in Photoshop. Ensure that the Layers palette is open (F7 key on the keyboard). I am using Photoshop CS3.
2. It is important not to directly edit the pixels on the original image (that would be ‘destructive editing’). Hence always make a copy of the Background layer. You do that by dragging the Background layer to the ‘Create a new layer’ icon at the bottom of the Layers palette.
3. Now go to the Blending mode and select ‘Multiply’. (click on the small downward pointing arrow where it says Normal and then click Multiply in the drop-down menu).
Observe that the blended image shows better tones in the background but the foreground and the rocks at the left have become too dark.
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There are two methods to proceed. Either create a white mask and paint away the dark areas with a ‘black’ brush (Foreground color should be black), or create a black mask (which will hide the effect of the Multiply blending mode) and then using a ‘white’ brush (Foreground color should be white), you paint away only on the areas you wish to darken (the sky area in our example). I am going to follow the black mask method.
4. Keeping Alt pressed click on ‘Add layer mask’ icon at the bottom of the layers palette. This will create a black mask which will hide the effect of the Multiply blending mode.
5. Finally, select the Brush tool (B) and using the brush’ hardness at zero, paint away the sky area to reveal the effect of the Multiply blending mode. Observe the black mask that you had created in step
4.The top of the mask turns white, indicating the area of the main image that was painted by you.
Rohinton Mehta
