Pict 1: This dull underexposed photo of a pot of Oden in Kyoto, Japan is typical of the flat snapshots churned out by many digital cameras.
Pict 2: After applying Colors > Auto > White Balance followed by Color Enhance, the Oden looks almost as delectable as when I ate it.
Yesterday, we used the Perspective and Crop tools in GIMP to correct perspective distortion and to crop a digital photo. Today, we make simple adjustments to darken or brighten a photo.
Modern digital cameras are rather intelligent in working out the right exposure for most snapshots. However, some photos may still end up too dark or bright for your liking. And dialling up the contrast tends to enhance the appearance of most photos.
GIMP has many ways of enhancing the exposure and contrast of a photo. Let’s start with the automated adjustments.
Automatic adjustments
(see Pictures 1 to 3)
Pict 3: Using Color Enhance in place of White Balance results in a less aggressive adjustment.
There are six quick one-click automatic adjustments in GIMP. They can be found under Colors > Auto in the main menu. These include: Equalize, White Balance, Color Enhance, Normalize, Stretch Contrast and Stretch HSV.
These commands adjust the brightness and contrast of a photo in different ways. Which command is most suitable depends on the nature of each individual photo.
Since it’s so easy to activate each adjustment, just try them on the photo one at a time to see which command yields the best effect. Press Ctrl-Z or Edit > Undo after each command to undo the previous adjustment before trying out the next adjustment.
From experience, I find White Balance gives the best result. Most of the time, applying White Balance followed immediately by Color Enhance may well be all that’s needed to both remove colour casts in photos and to improve the brightness and contrast at the same time.
If the results of using the White Balance adjustment is too exaggerated and contrasty, use Stretch Contrast as an alternative.
Brightness-Contrast command
(see Pictues 4 to 7)
Pict 4: Drag the Brightness and Contrast sliders and see the results in the photo.
Sometimes, none of the automatic adjustments work for a photo – or you may prefer more control over how the brightness/contrast is adjusted. In these cases, activate the Colors > Brightness-Contrast command from the main menu.
A dialog box with two sliders appears – the Brightness slider on top and Contrast slider below.
Drag the Brightness slider to the left to darken the photo or drag it to the right to lighten it. Drag the Contrast slider to the left to reduce the contrast and to the right to increase it.
Pict 5: Retro seems to be fashionable for small cars in Japan now. I snapped this sweet thing in Otsu on an overcast day.
Pict 6: Using Brightness:85 and Contrast:75 with the Brightness-Contrast command, the retro car looks more zappy now.
Pict 7: Using Brightness:100 and maximum Contrast:127 yielded a graphic art effect on the car.
Leave the Preview checkbox checked to see the effect of the adjustments on the photo while dragging the sliders. To compare the photos before and after the adjustments, toggle the checkbox on and off.
Once happy with the adjustments, hit the OK button.
To produce a graphics-art special effect from the photo, push the Contrast slider all the way to the right.
Powerpoint backgrounds
(see Pictures 8 to 10)
Pict 8: It is difficult to make out the text against the distracting background.
Many people use photos as backgrounds for their Powerpoint slides. Some end up making the text unreadable. Here’s a tip to avoid that happening.
Darken the photo (by dragging the Brightness slider to the left) when using light-coloured fonts for the text in the slide. Conversely, lighten the photo if the text in the slide uses dark-coloured fonts.
If the photo is still too distracting, use the Brightness-Contrast command with the Contrast setting lowered to beween zero and -50.
Pict 9: Light-coloured text is more readable against a darkened photo background.
Pict 10: Dark-coloured text is more readable against a lightened photo background.
Tomorrow, we’ll look at some alternative ways of adjusting exposure using Layers and Layer Modes.
