The Layers palette resembles a series of acetate sheets stacked one upon another. Where there is no image on part of a layer you can see straight through to the layer beneath it and where there is an image, you can adjust its transparency to control the degree to which the image below can be seen. You can cut out sections of an image and create a new layer that can be adjusted without affecting other parts of the image or use layers to combine several images into one.

Editing is the aspect of the workflow most subject to the photographer’s whims and level of expertise. It is easy to destroy a good image with excessive and inappropriate editing – but impossible to turn an inferior shot into a great-looking print. When editing images, make adjustments on a copy of the image file, keeping your original shot archived so you can return to it if the adjustments you apply don’t produce the results you want. If your software supports layers, make adjustments on an adjustment layer to see the effect they have before committing to them.


The Layers palette resembles a series of acetate sheets stacked one upon another. Where there is no image on part of a layer you can see straight through to the layer beneath it and where there is an image, you can adjust its transparency to control the degree to which the image below can be seen. You can cut out sections of an image and create a new layer that can be adjusted without affecting other parts of the image or use layers to combine several images into one.

To create a new adjustment layer, click on Layer then select New Adjustment Layer from the drop-down menu. This will open another drop-down menu that allows you to select the type of adjustment you wish to make. Different applications offer different adjustment tools but most will include Levels, Brightness/Contrast and Hue/Saturation adjustments, which are the most useful adjustment tools. In many cases, adjustments can be applied either uniformly across all colour channels or selectively to individual R, G and B channels. The latter allows very subtle colour corrections to be made.


You can also draw, edit, paste and reposition elements on one layer without affecting the other layers and, until you combine, merge or flatten all the layers in the image, each one will remain independent. Some applications include special features like layer masks and layer effects that allow you to create a wealth of special effects.

Because using layers is complex, we lack the space to cover it extensively in this pocket guide. Refer to the instruction manual supplied with your software application and spend time experimenting with the options on offer.

Adjustment Tools

Levels: The Levels control handles the tonal range in an image, which is displayed as a histogram with values ranging from 0 (black) to 255 (white). This plots the distribution of pixels (vertical axis) across 256 degrees of brightness (horizontal axis). A histogram that is weighted to the left side denotes an image with a high concentration of darker pixels, while one that is weighted towards the right represents an image in which light pixels predominate.

Most software applications provide Levels adjustments for the highlights, shadows and midtones and some allow you to adjust individual colour channels. All these adjustments can be used to make the image tonal range fit better into the printer’s output range or to correct for exposure problems when the shot was taken.

If you have captured the image correctly, a Levels edit is all that should be required to correct any minor flaws – and clicking on the Auto Levels setting may be sufficient (although watch for a possible unwanted colour shift in your image).

Most photos will print best when their tonal range is evenly distributed. However you need to make allowances to cope with images that should be printed with dark tones predominating (‘low key’ photos) and those in which light tones should dominate (‘high key’ photos).


To adjust tonal range and brightness using Levels click on Image>Adjustments>Levels for Photoshop or Enhance > Adjust Lighting > Levels for Photoshop Elements or Layers > New Adjustment Layer > Levels, or open an existing Levels adjustment layer. Make sure the Channel pop-up menu is set to RGB so your adjustment affects all three (red, green, and blue) channels. If you are working on a greyscale image, it will have the grey channel only.

Set the shadow and highlight values by dragging the left and right sliders directly below the histogram to the edge of the first group of pixels on either end of the histogram. You can also enter values directly into the first and third Input Levels text boxes. Some software applications can display individual histograms for the red, green and blue components in the image. These graphs can reveal when an image’s colour balance has been skewed and make correcting unwanted colour casts easier.


Tip: You can see which areas of the image will be clipped to black or white by pressing the Alt key (Windows) or Option key (Mac OS) as you drag a slider. As you drag the Shadow slider, black areas (while dragging the shadow slider) indicate which areas will be clipped to black (level 0). As you drag the Highlight slider, white areas (while dragging the highlight slider) indicate which areas will be clipped to white (level 255). Coloured areas show clipping in individual channels.


To adjust the brightness of the middle tones without affecting the shadow and highlight values, drag the grey Input Levels (middle) slider. You can also enter values directly in the middle Input Levels text box. (A value of 1.0 represents the current unadjusted midtone value.) Clicking OK allows you to see the effect of the adjustment in the histogram palette.


Auto levels adjustment spreads the tonal range in the image across the fill 255-step gamut, causing certain tones to ‘drop out’. These ‘gaps’ can be seen as a comb-like effect in the histogram. As long as they remain small, they are effectively invisible to normal vision.

The Auto Levels setting lets you map the midtones in the image to a neutral target by moving the highlight and shadow sliders automatically to the brightest and darkest points in each channel. This may also change some hues in the image.

However, if there are large gaps then you have effectively lost a great deal of data. While this may not show when displaying the image on the monitor, it can really degrade the print (see below). It’s generally best to edit with a light hand, especially if you’re working with JPEG files..


Almost all editing software includes brightness and contrast adjustments that act globally on the image. If you have adjusted an image with the Auto Levels control, these settings allow you to fine-tune the brightness and contrast in the shot. However, because the control applies a blanket adjustment across the entire tonal range, every pixel value in the image is adjusted by the same amount so you can easily lose highlight or shadow details if you move the slider too far – with either Brightness or Contrast.


Note the loss of highlight detail when the brightness adjustment is taken too far.

The latest versions of Photoshop and Photoshop Elements include a very useful highlight and shadow adjustment setting that is accessed by clicking Image>Adjustments> Shadow/Highlight. This powerful tool gives you complete control over densities within the image and supports subtle corrections as well.


Care must be taken when adjusting image brightness and contrast as over-adjustment can cause posterisation (see below) and ruin an otherwise excellent shot.


The Hue/Saturation tool usually contains three sliders: Hue, Saturation and Lightness. Each allows you to adjust specific values. Moving the Hue slider to either end of the scale changes all yellows to blue, all greens to magenta and all reds to cyan. Individual colour casts can be removed by selecting the relevant colour channel and moving the slider until the correct colour is achieved.


Moving the Saturation slider a little to the right increases colour saturation, while moving it left removes any excess colour saturation that may have been applied by the camera and restores colours to a more normal level. Moving it all the way to the left removes all colour information, creating a black and white picture.

The lightness slider can be used to lighten or darken the image. This slider acts globally, regardless of whether you select Master or a specific colour channel. It’s usually better to make such adjustments with the Levels control.


Printing Black and White Photographs outlines some other methods for producing and controlling B&W images. In all cases, it is best to keep the final image in RGB format, when you want a monochrome print. This is what printer drivers expect and, consequently, will yield the best quality print.


The Curves control, which is found in more sophisticated editing applications, works like a Levels adjustment with 16 settings combined with a graphic display of the highlights, shadows and midtones. Consequently, it’s a more precise tool for selectively tweaking a narrow range of tones than the Levels adjustment. For example, you can adjust the brightness and contrast in the shadows without changing values in highlight area – and vice versa.

When you open the Curves dialogue box you see a graph in which the horizontal axis represents the original brightness values of the pixels in the image (input levels) and the vertical axis represents the adjusted brightness values (output levels). The default diagonal line ranges from shadows in the bottom left of the graph, through midtones in the graph’s centre to highlights in the top right corner. The line is straight when the image is opened.


Adjustments are made by clicking on the part of the curve you want to adjust and moving that point up (to lighten that range of tones) or down (to darken it). You can also click on any points that you want to remain fixed to anchor them in place. Most applications with curve controls allow you to adjust the red, green and blue channels in the image separately.


Most software applications include a range of filters, many of which apply special effects. Unsharp masking is a useful tool provided in several image editing applications. Though it may sound counter-intuitive, this filter is used to correct some of the blurring that can be introduced during image capture, scanning, resampling or printing. Users can normally control the Amount of sharpening applied, the Radius of the edge-pixel area to which it is applied and the Threshold of difference between the sharpened pixels and those adjacent to them. Some experimentation will be required to become proficient with this tool.


Cloning and Healing Tools

The Clone tool (which is usually denoted by a rubber stamp icon) is one of the most useful tools in the editing palette. Not only can it be used for removing spots and scratches from image files, it can also be used to edit out distracting background details and smooth joins in stitched panoramas. Select the Clone tool and set the appropriate brush size from the drop-down menu.

Then choose a source area in the image that contains the colour and texture of the area you want to use to cover up the blemish. Alt-Click on this area to pick up the source data and then ‘paint’ over the area you wish to replace with the brush. This copies the pixels from the source area over the new area.


Cloning has been used to eliminate the fluorescent light strips and person entering the building.

Photographers have plenty of control over the Clone tool. As well as adjusting brush size, you can also control the diffuseness of its edges, its opacity, flow and the blend mode (which influences the way the copied pixels interact with the underlying pixels). Proper use of the Clone tool requires practice. Change the brush size and the source area constantly to avoid the telltale stair-stepped look that results from repeated use of the same source material.

The Healing Brush tool works similarly to the Clone tool but samples and matches the texture, lighting, and shading of the sampled pixels to the source pixels. This means that the repaired pixels blend seamlessly into the rest of the image. It can be used to remove wrinkles and blemishes from skin, fine-tune cloned areas, eliminate scratches and dust spots.


The main problem with the Healing Brush is that it doesn’t work well on edges that have different hues and/or contrasts. For this reason, some newer applications have introduced a Spot Healing Brush, which has tighter edges. Unlike the Healing Brush, the Spot Healing Brush doesn’t require you to make a selection or define a source point before using it. It’s particularly useful for removing spots and scratches when restoring old photographs.

8-bit vs 16-bit Editing

Image bit depth plays an important role in the end results you can obtain when you edit digital images. Photographers who shoot JPEG images always end up with 8-bit image files because that’s the only bit depth supported in the JPEG format. This restricts the adjustments they can make because image data is easily lost when adjusting Levels in editing software. When data is lost, intermediate tones ‘drop out’ and the picture becomes posterised, as shown in the “cat” illustration above and below in Posterisation.

Photographers who shoot raw files have the option of converting them to 16-bit TIFF files, which have three times as much data as a JPEG file at the same capture resolution. This gives them three times the adjustment flexibility and minimises the risk of posterisation.

Note: Many entry-level image editors only support 8-bit editing so, if you’re serious about obtaining top picture quality, choose an editor that supports 16-bit adjustment, such as Adobe’s Photoshop Elements. More information on the benefits of 16-bit editing can be found in Printing Raw Files section.


The histograms overlaid on these sample images show the difference between 8-bit and 16-bit editing. After a levels adjustment, the histogram for the 8-bit image takes on a ‘comb-like’ structure, with the gaps in the graph denoting tones that have ‘dropped out’ as a result of the edit. The histogram for the 16-bit edit (above) retains its continuous structure, indicating that no tones have been lost.


When using some editing tools, it is easy to produce radical shifts in the distribution of tones in the image, producing posterisation. Posterisation results when the smooth gradation of continuous tones in an image is disrupted and some tonal bands ‘drop out’, leaving the image rendered in bands of colours. It is very easy to produce posterisation with the Curves control – especially when the curve becomes S-shaped (as shown in the illustration). The Shadow/Highlight tool can also produce posterised results when adjustments are excessive.

The Levels control is much less likely to destroy image data and produce posterisation as its end result. Always check adjustments that may cause images to become posterised by enlarging a section of the image. Posterisation is surprisingly common as slight posterisation can be difficult to detect on a monitor. However, even a small degree of posterisation can ruin an otherwise excellent print.




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