Levels

Levels was covered in Tutorial #1 but is also included here as a tonality and colour adjustment tool. The Levels tool enables amendments to three tonal parts of an image, namely highlights, midtones and shadows. When the Levels dialog box is open a histogram is shown which displays the distribution of tones in an image as a 256 step greyscale from pure black to pure white (see dialog box below).

The horizontal greyscale (Input Level) adjusts contrast by moving the black and white point sliders, while the grey point slider adjusts midtones. If the histogram display falls away before reaching the black and white point sliders, moving the sliders towards the edge of the histogram resets the image black and white points.

Moving the greypoint slider towards the white point slider darkens midtones, while moving it towards the black point slider lightens midtones.

If the Preview check box is clicked, adjustments are shown in the thumbnail image in the dialog box. Alternatively, you can preview the effect on the full size image by clicking the Preview button on the dialog box.


Because these simple adjustments often make significant improvements to a photos tonal range, checking and adjusting levels is often a good starting point with any image editing work.

Tone Map 1 (Preset Enhancements)

While Levels allows adjustment of three image areas, namely highlights, midtones and shadows, Tone Map allows up to 11 points for adjusting an images tonal range.

As with Levels, the histogram in the dialog box shows the distribution of tones in an image as a 256 point greyscale, with black on the left and white on the right of the horizontal scale. In addition, there is a line which can be moved and adjusted to alter the tonal range of the image. This line can be adjusted either using the preset enhancements from the pull down menu, or by adding customised control points to change the shape of the line, which then changes the images tonal range.

In the dialog box above, one of the preset adjustments (Darken Midtone) has been selected and applied to the Master channel. Similar adjustments can be made to the Red, Green and Blue (RGB) channels if required. The effects of any adjustments are shown in the righthand thumbnail.

Tone Map 2 (Custom Enhancements)

If Tone Maps preset enhancements do not give the type of results required, you can produce your own custom adjustments by adding Control Points and dragging the line to remap the tonal distribution. To add a Control Point, select Custom from the Enhancement pull down menu, then use the mouse to click one or more points on the line. When the points have been added, use the mouse to drag each point into its new position. The effects of these changes will show in the righthand thumbnail image.

Its also possible to add Control Points to Tone Maps preset enhancements for further adjustment and refinement. After selecting an option from the Enhancement pull down menu, click the Use Control Points box, then click points on the line that you wish to adjust, and drag these into their new positions.

Individual Control Points can be removed by selecting the point with the mouse, right clicking, and selecting delete. To remove all Control Points you have added, click the Reset button.

In the example left, two Control Points have been added to the line related to shadow areas and midtones. The shadow area Control Point (bottom left) has been dragged downwards slightly to darken shadow areas of the image. The midtone Control Point was not moved, but added to keep midtone areas unchanged. This has changed the line from being straight, into a slight S shaped curve, which for many reasonably exposed photographs will give a good tonal distribution from black to white (and other colours in between). Photographs with more under or over-exposure will probably require a larger degree of adjustment.

Brightness and Contrast

Brightness and Contrast controls are, as the name suggests, used for adjusting an images brightness and contrast levels. Adjustments can be made by moving sliders or clicking on thumbnails. Higher numbers on the slider controls produce higher levels of brightness and contrast. Use the Gamma slider for adjusting midtones.

Adjustments can be made to both the Master channel and Red, Green or Blue channels if required. When an adjustment is made with the slider controls, the effect of this adjustment is displayed in the middle thumbnails display (with a blue border around it). This setting can be saved if required to apply to other images. To save the setting, click on the Add button, give the selection a name and save in the Easy Palette for later use.

The Show Clipping display can be used to show on thumbnails which parts of the image will be converted to pure black or pure white as a result of selected brightness and contrast adjustments. This is useful for making sure shadow areas do not become too dark, or highlight areas become burnt out.

The Thumbnail variation slider controls the amount of variation, in terms of brightness and contrast, between the thumbnail images for selecting adjustment. Higher numbers increase contrast while lower numbers reduce contrast.

When the Brightness and Contrast dialog box is open, the default setting for thumbnails shows the whole image. This can be changed by clicking on the Thumbnail button (which opens the dialog box shown left) and selecting an alternative view, for example, zooming in to an area of specific interest. Click OK to return to the Brightness and Contrast dialog box, and the thumbnail view changes to the selected method.