Tech bytes for tea?

This basic adjustment command uses a rudimentary algorithm that treats all pixels equally and adjusts them to the same extent. It’s useful if all you need is a quick and dirty adjustment to the photo.

For almost the same effort, the Levels command provides better control and the algorithm yields better results adjusting pixels to different extents depending on the settings you make.

That is why for many free photo editors, more advanced tools like the Levels and Curves command are not available or are only available when you upgrade to a paid version. In GIMP, these tools available for free.

Using the Levels command

Pict 3: This photo of a hanging potted plant is slightly underexposed because the camera has been fooled by the bright background.

Pict 4: The red petals are now more vibrant and discernible after the photo has been enhanced with the Levels command in GIMP.

Last week, we looked at how to analyse a photo’s characteristics and problems by examining its histogram in GIMP.

Using the histogram as a basis, we’ll learn to use the Levels command to improve the tonal distribution of a photo such that the overall brightness and contrast of the photo is just right and the entire range of brightness values (from 0 to 255) available is fully utilised.

With the photo open in GIMP, choose the Colors > Levels command from the main menu. A complicated looking Levels dialog box pops up showing a histogram of the photo as well as many controls and input fields to control the histogram is to be adjusted.

The reason why many beginners hesitate to use the Levels command is the seeming complexity of the dialog box. But in most cases, all you need is to drag one to three of the triangular sliders directly below the histogram. Here’s how.

Darkening a photo

Pict 5: Busy bee working on Lavender flowers in Provence, south of France.

Pict 6: The photo after darkening using the Levels command in GIMP.

Pict 7: Drag the triangular slider from the left edge inwards towards the right.

The three boxes below the histogram shows the numeric brightness values of where the sliders are. It serves as a reference or when you need to key in specific numeric values to use. Most of the time, you should simply drag the slider inwards based on where the bulk of the histogram begins.

Dragging the blackpoint slider to 60 tells GIMP to darken pixels of brightness 60 and below down to zero. The other pixels in the histogram are correspondingly darkened as well. This also increases the overall contrast of the photo because a wider range of brightness value is now used in the photo.

To further finetune the brightness of the photo, drag the centre slider to the left or right to lighten or darken the mid-tones.

Lightening a photo

Pict 8: Drag the triangular slider from the right edge inwards towards the left.

For the slightly underexposed photo of the potted flower on the wall, the histogram stops short at around the brightness level 210. Drag the whitepoint triangular slider from the right edge inwards towards the left until it is at the point where the main bulk of the histogram ends (see Pictures 3, 4 and 8 ).

Dragging the whitepoint slider to 210 tells GIMP to set 210 as the white point – all pixels that are of brightness 210 and greater are increased to the maximum of 255. The other pixels are correspondingly lightened as well.

As before, the overall contrast of the photo is increased because the entire range of brightness values is now used in the photo.

Again, drag the centre slider to the left or right to lighten or darken the mid-tones further.

Adjusting all three sliders

The snapshot of the port of Marseilles was taken on an overcast evening and is not only too dark but sorely lacking in contrast, resulting in a dull and flat photo (See Pictures 1 & 2).

Pict 10: The histogram is now spread across the entire range of brightness.

The histogram in the Levels dialog box shows that all the pixels are bunched up in the mid-tones – there are now extreme white or black pixels – so the highlights are not bright enough while the shadows are not dark enough.

Pict 9: Drag the blackpoint and whitepoint triangular sliders from both edges inwards.

In this case, drag the blackpoint and whitepoint sliders inwards to where the bulk of the histogram begins and ends (see Picture 9). This darkens the shadows and lightens the highlights forcing the bunched up histogram to spread out across the entire range of brightness – thereby increasing the overall contrast of the photo.

As the photo is still too dark, drag the centre slider to the left to further brighten the photo.

The resulting histogram after the adjustment is now spread out across the entire brightness range (see Picture 10).

Make a poster or postcard from your favourite photo.

Ever wanted to make a postcard or a poster from your favourite photo? Here are some techniques using layers and layer masks in GIMP.

Add a grid of white dots

Open the photo in GIMP. From the Layers dialog, you can see it resides in the Background layer which is the only layer for the moment.

The original photo from morguefile.com.

A grid of white dots is overlaid onto the photo.

A new empty layer filled with white is added above the original photo in the Background layer.

Right-click on its thumbnail in the Layers dialog and select “Add Layer Mask” command from the pop-up menu. In the “Add Layer Mask” dialog box that pops up, select the “White (full opacity)” option and press the OK button. A layer mask filled with white is added to the layer – you can see its thumbnail beside the original thumbnail in the Layers dialog.

Use the Grid filter to create the grid of white dots.

From the main menu, select the “Filters > Render > Pattern > Grid” command. In the Grid dialog box that pops up, increase the horizontal width setting until the preview in the dialog box shows a grid of white dots of the desired size. Here I used a setting of 13.

The white layer now appears as a grid of white dots overlaid on the original photo.

Right-click on the upper layer in the Layers dialog and select “Apply Layer Mask” to merge the layer mask into the original solid white layer. The layer mask is removed and the layer becomes a transparent layer with a grid of white dots overlaid on the photo below.

Hiding the white dots from the heads and faces

Use a layer mask to hide the white dots from the heads.

Add a new layer mask on this layer, again selecting the “White (full opacity)” option in the  “Add Layer Mask” pop-up dialog box.

Press “D” on the keyboard to reset the Foreground colour to black. Activate the Paintbrush Tool from the Toolbox and paint on the layer mask in the image window. Paint around the heads and faces of the wedding couple to hide the white dots in that area.

From the main menu, select the “Layer > New from Visible” command to create a new layer that combines all the visible layers in one layer.

Adding the green arc

In the Layers dialog, click to select the layer below the new combined layer. This is so that any new layers created will be added BELOW the combined layer.

Zoom out until the photo is smaller than the image window.

Set the Foreground colour to green (or your preferred colour). Add a new layer by clicking the icon at the bottom left corner of the Layers dialog. In the “New Layer” dialog box that pops up, select the radio button for “Foreground color” option under Layer Fill Type and press the OK button.

A new layer filled with green is added just below the combined layer.

Right-click the combined layer in the Layers dialog to add a layer mask to the layer, using the “White (full opacity)” option. Press the minus key (“-”) on the keyboard to zoom out the view in the image window.

As the photo becomes smaller than the image window, you will see white space between the edges of the photo and the edges of the image window.

Adding a green arc at the bottom of the poster.

Activate the Ellipse Select Tool from the Toolbox and drag an elliptical selection around the couple’s heads. You can begin dragging in the white space between the photo and the edge of the image window so that the elliptical selection covers most of the photo except for a small arc at the bottom of the photo.

Remember you can adjust the size and position of the elliptical selection by dragging the side or corner control handles of the selection outline. Once happy with the selection, use the “Select > Invert” command from the main menu to invert the selection.

Press “D” on the keyboard to reset the Foreground colour to black. Select the “Edit > Fill with FG Color” command to fill the arc with black (in the layer mask).

An arc of green is revealed below the photo.

Adding the white highlight

Click on the green layer in the Layers dialog to select it.

Add a white highlight band in the green arc.

Add another new layer, this time selecting the radio button for “White” option under Layer Fill Type. The new white layer is added above the green layer but below the combined layer.

Add a layer mask to the white layer, selecting the “Black (full transparency)” option in the pop-up dialog box. A layer mask filled with black is added to the layer.

Press “D” to reset the Background colour to white. Using the Rectangle Select Tool from the Toolbox, select a vertical band and use the “Edit > Fill with BG Color” command from the main menu. A white band is added to the layer mask such that a white band runs through the green arc.

Adding the text captions

GIMP's Layers dialog.

Click the combined layer (the topmost layer) in the Layers dialog to select it, so that any text captions added will be added above it.

Activate the Text Tool from the Toolbox. In the Tool Options below the Toolbox, set the font, size and colour settings for the Text Tool. Click in the white band in the arc with the cursor and type the word “Wedding”. Click in the green portion to add the word “Kiss”.

After adding the captions, you can still change the font, size and colour setting for these captions by selecting them first with the Text Tool and then modifying them in the Tool Options.

Add edge shadow

Add a new empty layer right at the top of all other layers. Activate the Blend Tool from the Toolbox. Press “D” to reset the Foreground colour to black and the gradient to “FG to Transparent”.

Again, zoom out the photo (by pressing the minus key on the keyboard) until the photo is smaller than the image window. Drag a black-to-transparent gradient from outside the right edge of the photo (but inside the right edge of the image window) to slightly inside the right edge of the photo.

Save the file in .xcf format so that you can come back to tweak the design in the future. Save as .jpg to send the file for print at the studio.