An international standard for color measurements developed by the Commission Internationale de L’Eclairage (CIE).

It’s capable of reproducing all the colors of RGB and CMYK and uses three channels - one for luminosity and the other two for RGB type color ranges.

Some users prefer to work in this mode as it’s device independent and colors that fall into the CMYK gamut aren’t changed when you convert to CMYK.

One of the many ways that you can organize the files that are displayed in the Bridge workspace is by attributing a label to the picture.

In CS2 and CS3 the labels option is supplied in two forms - a color tag, called Label (2) or star value, called Rating (4). Either or both (3) label types can be applied to any picture.

Labels are attached by selecting the thumbnail(s) in the workspace and then choosing the desired label from the list under the Label menu (1). Keyboard shortcuts are also provided for each label option making it possible to quickly apply a label to a thumbnail or group of thumbnails. The label tag can then be used to sort or locate individual pictures from groups of photos.

As the name suggests, the Lasso tools are designed to capture picture parts by surrounding them with a drawn selection marquee (1).

The standard Lasso tool (2) works like a pencil, allowing the user to draw freehand shapes for selections. In contrast, the Polygonal Lasso tool draws straight edge lines between mouse-click points. Either of these features can be used to outline and select irregular-shaped image parts. A third version of the tool, the Magnetic Lasso, helps with the drawing process by aligning the outline with the edge of objects automatically.

For most tasks, the Magnetic Lasso is a quick way to obtain accurate selections, so it is good practice to try this tool first when you want to isolate specific image parts.

Once a filter has been used to change the appearance of a picture, it can be reapplied using the same settings by selecting the filter’s name from the top of the Filter menu. As a shortcut alternative the Ctrl and F keys can be pressed (Command F for Macintosh).

To reapply the last filter but allow for the settings to be changed via the filter’s dialog use the Ctrl Alt F keystroke combination (Command Option F for Macintosh).

This feature, introduced with version 6.0, lets you cut up, or slice, your picture into several pieces. Then when the image is used in a web page each slice is saved as an independent file with a piece of HTML code containing instructions for recombining the photo so that it appears as a single image.

The HTML code contains color palette info and links, rollover effects, and animations can be added in ImageReady (in versions previous to CS3). Slices help you gain faster download speeds and increased image quality.

Apply a layer-based slice on a layer with a selection and the slice will be positioned around it. This can then be moved and scaled using the Move tool.

In the example a selection was made around the fishing reel and this was copied and pasted onto a new layer. Now when you request a New Layer Slice it appears around the selection and can be set to be used as a hot link on a web page.

A layer clipping mask is used to control what section of lower layers is hidden and what parts are displayed. The bottommost layer is used as the mask with solid areas - picture parts - displaying the contents of the grouped layers above and the transparent areas letting the layers beneath show through.

In this way the feature is often used to insert the contents of one layer into the non-transparent areas of another. The example shows the flag image (top layer) being clipped by the flower shape layer (non-transparent areas) of the middle layer with the bottom gradient layer showing through.

Only the flag and the flower layers are part of the clipping mask. The effect occurs because all the layers in the clipping group have the opacity attributes and blend mode of the bottom-most layer in the group (1).

You can create a clipping mask in two different ways:

1. Select the top layer and then choose Layer > Create Clipping Mask.

2. Hold down the Alt/Opt key whilst you click on the boundaries between the two layers you wish to group.

To unclip a set of layers, select the bottom layer in the group (name underlined) and then choose Layer > Release Clipping Mask.

Layer Comps is a feature that first appeared in CS. It lets you create a snapshot of a state of the Layers palette.

Layer Comps records a layer’s position in the Layers palette and whether it’s showing or hidden. It also records whether layer styles are applied. This is a useful feature if you want to try different effects to show a client. You can then turn each version on or off in the Layer Comps palette and view the differences with speed.

To make a new layer comp arrange the layer content, styles and opacity and then click the Create New Layer Comp button at the bottom of the palette. Insert a name for the comp in the dialog that is displayed and click OK. The new comp appears in the palette.

To display a comp click on the empty box at the left of the comp name. To cycle through all comp options (from top to bottom) press the Apply Next Selected Layer Comp button (right arrow) at the bottom of the palette.

The bottom-most layer of any layer stack is called the background layer.

By default this layer is locked, which means that you cannot change its position in the layer stack, its opacity or the blend mode. In order to make these type of changes to the background layer it must be first converted to a standard image layer. This can be achieved by making the background layer active (click on the layer) and then choosing the Layer From Background option from the Layer > New menu (1). Alternatively, double-clicking the background layer in the Layers palette will perform the same function.

After multi-selecting at least two layers in the Layers palette (1) you can move these layers into a new Layer Group (2) by selecting Group Layers from the Layer menu.

To ungroup a set of layers select the group first and then choose Layer > Ungroup Layers.

Layer Groups are a collection of layers that have been moved into a single layer folder. When working with a complex picture that contains many layers, grouping layers into logical folders makes their management easier and the Layers palette less crowded. Layers can be dragged into an existing folder from elsewhere in the palette or placed into a newly created group folder by multi-selecting and then pressing the Create New Group button at the bottom of the palette. In previous versions this feature is referred to as Layer Sets.

Each time you add a fill or adjustment layer to an image two thumbnails are created in the Layers palette. The one on the left controls the settings for the adjustment layer (1). The thumbnail on the right represents the layer’s mask that controls how the adjustment is applied to the picture ( 2 ).

The mask is a grayscale image. When it’s colored white no part of the layer’s effects are masked or held back from the picture below. Conversely, if the mask thumbnail is totally black then none of the layer’s effects are applied to the picture. Shades of gray equate to various levels of transparency. In this way the adjustment or fill layer can be selectively merged with the picture beneath by painting (in black and white and gray) directly on the layer mask thumbnail.

The opacity or transparency of each layer in Photoshop can be changed independently. Depending on the level of opacity the parts of the layer beneath will become visible. Change the opacity of each layer by moving the slider in the Layers palette. A value of 100 % means the layer is completely opaque, 50% translates to half transparent and 0% means that it is fully transparent.

Just like the new Layer Groups in Photoshop CS2, the Layer Sets used in previous versions of the program are designed to help organize the many layers that combine to form a complex Photoshop document.

Whilst the layers reside in the Layer Set they can be hidden, modified, moved and locked as a single entity.

To create a Layer Set in Photoshop CS click on the Create New Layer Set button at the bottom of the Layers palette. Click and drag layers from the palette into the new set. The layers that reside inside a set are indented in the palette.

sets can also be nested inside other sets creating a hierarchy of layers.

Photoshop CS3 Extended introduces a new way to compare and contrast the content of several layers in the Layers palette. Called Stack Mode, the feature can be used for a range of advanced enhancement techniques.

• 1. Using Stack Mode is a three-step process. Firstly, the separate source images are layered in a single document and auto aligned to ensure registration of important details.
• 2. Next the layers are multi-selected in the layer stack and converted to a Smart Object (Layer > Smart Object > Convert to Smart Object).
• 3. Now the method, or rendering option, used for comparing the content of the layers is selected from the Layer > Smart Object > Stack Mode menu.

Photoshop CS3 Extended contains a range of analysis or rendering options in the Stack Mode menu. These options manage how the content of each of the layers will interact with each other.

One example of how Layer Stack Mode analysis can be used is in the case of Noise reduction (see before and after images). With this technique the Median option is used to create a composite result retaining only those image parts that appear (in the same spot) in more than 50% of the frames (layers). As noise tends to be random, its position, color and tone changes from one frame to the next and so it is removed from the rendered photo leaving just the picture itself.

Layer Styles, sometimes referred to as layer effects, are a set of preset effects that can be applied to the contents of a layer by simply clicking a thumbnail in the Layer Styles palette.

When a style is applied to the contents of a layer a small ‘f’ appears to the right end of the layer in the palette (1). The style effects are now linked with the layer and will move and change as the content is edited.

Multiple styles can be applied to a single layer and their effects can be cleared or hidden using the options in the Layer > Layer Styles menu. The individual settings used for the style can be adjusted by doubleclicking the Effects area (2) of the palette and then changing the settings in the Layer Style dialog.

The Layer via Copy command creates a new layer and copies the contents of the current selection onto it.

The Layer via Cut command cuts the contents of a selection, creates a new layer and pastes it into the layer.

If the detail is cut from a background layer then the empty space is filled with the background color. When the detail is cut from a layer the space is left transparent.

When downloaded straight from the camera digital photographs are flat files with all the picture parts contained in a single document, but Photoshop also contains the ability to use layers with your pictures.

This feature releases your images from having to keep all their information in a flat file. Different image parts, added text and certain enhancement tasks can all be kept on separate layers. The layers are kept in a stack and the image you see on screen in the work area is a composite of all the layers.

Sound confusing? Well try imagining, for example, that each of the image parts of a simple portrait photograph is stored on separate plastic sheets. These are your layers. The background sits at the bottom. The portrait is laid on top of the background and the text is placed on top. When viewed from above the solid part of each layer obscures the picture beneath. Whilst the picture parts are based on separate layers they can be moved, edited or enhanced independently of each other.

When layered files are saved in the PSD or Photoshop file format all the layers will be preserved and present the next time the file is opened. Photoshop supports the following layer types:

Image layers - This is the most basic and common layer type and contains any picture parts or image details. Background is a special type of image layer (3).

Text layers - Designed solely for text, these layers allow the user to edit and enhance the text after the layer has been made (1). They are vector-based layers and must be simplified (rasterized) to apply a filter or to paint on. Adjustment layers - These layers alter the layers that are arranged below them in the stack. They act as a filter through which the lower layers are viewed (2). You can use adjustment layers to perform many of the enhancement tasks that you would normally apply directly to an image layer without changing the image itself.

Fill layers - Users can also apply a Solid Color, Gradient or Pattern to an image as a separate layer. These three selections are available as a separate item (Layer > New Fill Layer) under the Layer menu or grouped with the adjustment layer options via the quick button at the bottom of the Layers palette.

Smart Object layers - A Smart Object layer is a special layer that encapsulates another picture (either vector or pixel based). As the original picture content is always maintained any editing actions, such as transforms or filtering, that are applied to a Smart Object layer are non-destructive.

3D layers (extended only)- Photoshop CS3 Extended also has the ability to open and work with 3D architectural or design files.

Shape layers - Drawing with any of the shape tools creates a new vector-based shape layer. The layer contains a thumbnail for the shape as well as the color of the layer. Background layers - An image can only have one background layer. It is the bottommost layer in the stack. No other layers can be moved beneath this layer and you cannot adjust this layer’s opacity or its blending mode (4).

By default Photoshop classifies a newly downloaded picture as a background layer. You can add extra ‘empty’ layers to your picture by clicking the New Layer button at the bottom of the Layers palette. The new layer is positioned above your currently selected layer. Actions, such as adding text with the Type tool, automatically create a New Layer for the content. When selecting, copying and pasting image parts, Photoshop also creates a new layer for the copied portion of the picture.

The way that layers are linked changed with the release of Photoshop CS2.

In previous versions of Photoshop layers were linked by clicking in the link box on the left of the layer but now linking several layers is a simple matter of multi-selecting the candidate layers and then pressing the Link button (1) at the bottom of the Layers palette.

A Link or Chain icon is then displayed on the right of the individual layers that are linked together ( 2 ).

Once layers are linked the relationship of the content of each layer is fixed and all picture parts move together when one layer is repositioned.

To unlink a group of layers select any layer in the linked set and click on the Link button at the bottom of the Layers palette.

In CS2 and CS3 layers can be more easily grouped, moved and managed than in previous releases of the program. It is now possible to multi-select layers inside the Layers palette using the same keystrokes employed for selecting thumbnails in Bridge.

Select a group of layers - Click on the top-most layer and then hold down the Shift key and click on the bottom-most layer in the group. All layers between these layers and the layers themselves will be selected ( 1 ).

Select individual layers - Select the first layer and hold down the Control key (Command - Mac) and select the other individual layers ( 2 ).

In addition to selecting layers in the Layers palette you can also select groups of layers that combine to make up an image part by dragging a Move tool marquee around the image area. For this feature to work the Auto Select Layer and Auto Select Groups options must be selected in the Move tool’s options bar (3).

The Layers palette displays all your layers and their settings in the one place. Display the palette by selecting Window > Layers. Individual layers are displayed, one on top of the other, in a ‘layer stack’. The composite image you see in the workspace is viewed from the top down through the layers. Each layer is represented by a thumbnail on the left and a name on the right.

You can edit or enhance only one layer at a time. To select the layer that you want to change you need to click on the layer. At this point the layer will change to a different color from the rest in the stack and is now called the active layer (3).

Layers can be hidden from display in the workspace by clicking the eye symbol (4) on the far left of the layer so that it is no longer showing. This action removes the layer from view but not from the stack. You can redisplay the layer by clicking the eye space again.

The blend mode (1) and opacity (2) of individual layers can be altered using the controls at the top of the palette. New layers (5) as well as new adjustment layers ( 6 ) can be created by clicking the buttons just below the Blend and Opacity controls. The Dustbin button (7) is used to delete unwanted layers and the Lock Transparency ( 8 ) and Lock All (9) buttons are used to restrict layer changes.

Originally referring to the small pieces of lead that were placed in between lines of metal type used in old printing processes, nowadays it is easier to think of the term referring to the space between lines of text.

Smaller values reduce the space between lines ( 1 ) and larger numbers increase this space ( 2 ).

Photoshop includes the ability to alter the leading of the type input in your documents. The leading control can be found in the Character dialog (3).

Start with the Auto setting or a value equal to the font size you are using and increase or decrease from here according to your requirements.

The sophisticated Lens Correction filter (Filter > Distort > Lens Correction) first introduced in Photoshop CS2.

The feature is specifically designed to correct the imaging problems that can occur when shooting with different lenses. Apart from correcting Barrel and Pincushion distortion, the filter can also fix chromatic aberration or color fringing (color outlines around subject edges) and vignetting (darkening of the corners) problems that can also occur as a result of poor lens construction. Controls for changing the perspective of the picture (great for eliminating the issue of converging verticals) as well as how to handle the vacant areas of the canvas that are created after distortion correction are also included.

The example image, photographed with a wide-angle auxiliary lens, displays both Barrel distortion and converging verticals that are in need of correction.

1. With a suitable image open select Filter > Distort > Lens Correction. Adjust the Zoom control and drag the grid with the Move Grid tool, so that it aligns with a straight edge in the photo. Adjust the Remove Distortion slider to the right to correct the barrel effects in the picture. Your aim is to straighten the curve edges of what should be straight picture parts.

2. Now concentrate on correcting the converging verticals. Move the Vertical

Perspective option to the left to stretch the details at the top of the photo apart and condense the lower sections. Again aim to align straight and parallel picture parts with the grid lines.

3. If necessary, lighten the edges of the image by moving the Amount slider to the right and adjusting the percentage of the picture that this control affects with the Midpoint control.

4. Zoom in to at least 600% to check for chromatic aberration problems and use the Fix Red/Cyan Fringe or Fix Blue/Yellow Fringe controls to reduce the appearance of color edges. Click OK to apply the correction settings. Crop the ‘fish tail’ edges of the corrected photo to complete.

The Lens Flare filter, as one of the group of Render filters, adds a bright white spot to the surface of photos in a way that resembles the flare from light falling on a camera lens.

This filter is often used when light sources such as the sun, a street lamp or car headlights are part of the picture.

The filter dialog contains a preview thumbnail on which you can position the center of the flare by click-dragging the cross hairs (1). Also in the dialog is a Brightness or Strength slider (2) and a selection of lens types to choose from (3).

The filter has been revamped for CS2 so that it can also be used in 16 bits per channel mode.

You can set the Lens Flare center precisely by Alt/Opt-clicking on the preview image and then inputting the X and Y coordinates for the center of the effect.

Looking very similar to the Histogram, this feature allows you to interact directly with the pixels in your image.

As well as a graph (1), the dialog contains two slider bars. The one directly beneath the graph has three triangle controls for black (2), midtones (3) and white (4), and represents the input values of the picture.

The slider at the bottom of the box shows output settings, and contains black (5) and white ( 6 ) controls only.

To distribute the picture tones across the whole of the spectrum, drag the input shadow (left end) and highlight (right end) controls until they meet the first set of pixels at either end of the graph. When you click OK, the pixels in the original image are redistributed using the new white and black points.

Altering the midtone control will change the brightness of the middle values of the image, and moving the output black and white points will flatten, or decrease, the contrast.

Clicking the Auto button is like selecting Image > Adjustment > Auto Levels from the menu bar.

To help you gauge the darkest and lightest points hold down the Alt key (Option on a Mac) whilst you click on the white or black triangle.

This creates a posterized image showing the lightest point as white and the darkest point as black. As you drag the markers inwards you will see the white or black areas increase over the picture. This will give you an indication of how far to drag the sliders to make effective use of clipping the image. Use the values displayed as your highlight and shadow points.

The Lighten blending mode is one of the group of Lighten modes that base their effects on combining the light tones of the two layers.

Both top and bottom layers are examined and the lightest tones of either layer are kept whilst the darker values are replaced. This mode always produces a lighter result.

The Lighting Effects filter, as one of the group of Render filters, simulates the look of various light sources shining onto the picture surface. Single or multiple light sources can be added to the photo.

The filter dialog contains a preview thumbnail that is used to adjust the position, shape and size of the projected light (1). The rest of the dialog is broken into four different control sections:

Style (2) - Provides a drop-down menu of pre-designed light styles along with any customized styles you have created and saved.

Light type (3) - Alters the color, intensity and focus of the selected light.

Properties (4) - Contains controls for how the subject reacts to the light.

Texture Channel (5) - Has options for creating texture with the light shining onto the photo.

This feature is often used for creating, or enhancing existing, lighting type effects on the main subject in a picture.

An image that’s drawn using one color on a background color with no midtones.

Line art is a popular giveaway on royalty-free CDs and websites. This frog was found on www.free-graphics.com, a website with over 130,000 free graphics for use when downloaded.

I’ve picked a small sized one to show you what happens to line art if the file size is too small. It looked sharp on screen, but here in print it looks smudged so choose with care.

The Linear Burn blending mode is one of the group of Darken modes that base their effects on darkening the picture by adjusting the brightness of the blended image. This option analyzes the brightness of the details in the top and bottom layers and darkens the bottom layer to reflect the tone of the top layer. The filter always produces a darker effect and blending with a white top layer produces no change.

The Linear Dodge blending mode is one of the group of Lighten modes that base their effects on lightening the picture by adjusting the brightness of the blended image.

This option analyzes the brightness of the details in the top and bottom layers and brightens the bottom layer to reflect the tone of the top layer.

The filter always produces a lighter effect and blending with a black top layer produces no change.

Photoshop has five different gradient types. All the options gradually change color and tone from one point in the picture to another.

The linear gradient (1) changes color from start to end point in a straight line.

To create a gradient start by selecting the tool and the linear gradient type (2). Then adjust the controls in the Options palette.

Choose the colors from the Gradient Picker drop-down menu and the style from the five buttons to the right.

Click and drag the mouse pointer on the canvas surface to stretch out a line that marks the start and end points of the gradient. Release the button to fill the layer with the selected gradient.

The Linear Light blending mode is one of the group of Overlay modes that base their effects on combining the two layers depending on the tonal value of their contents.

This option combines both burning and dodging of the picture in the one mode.

If the tone in the top layer is lighter than 50% then this section of the bottom layer is lightened; if the tone is darker, then it is darkened.

Blending with 50% gray produces no change.

The Line tool is one of the vector-based shape tools. Unlike the Brush or Pencil tool, which draws with pixels, the lines created with this tool are always sharp edged and high quality.

To create a line with the tool click and drag on the canvas surface. Holding down Shift when drawing restricts the tool to drawing straight lines at intervals of 45°.

The options bar for the tool contains the following settings:

Arrowhead start and end - Determines which end of the line an arrowhead will be added. Leaving the boxes unchecked creates a line with no arrowheads.

Arrowhead width and length - Sets the width of the arrowhead at the base and the overall length of the head based on a percentage of the line weight.

Concavity - Determines the degree to which the arrowhead is concaved as a percentage of the total length of the head.

Weight - Controls the thickness of the line in pixels.

Color - Sets the line color.

Style - Determines if a layer style is automatically added to the line as it is drawn.

• (1) 3 pixels weight, black.
• (2) 10 pixels weight, gray.
• (3) 20 pixels weight, red, arrowheads start and end.
• (4) 20 pixels weight, chrome style, arrowheads start and end.

The Liquify filter is a very powerful tool for warping and transforming your pictures. The feature contains its own sophisticated dialog box complete with a preview area and no less than ten different tools that can be used to twist, warp, push, pull and reflect your pictures with such ease that it is almost as if they were made of silly putty. In CS2 the filter also works with 16-bit images. The effects obtained with this feature can be subtle or extreme depending on how the changes are applied. Stylus and tablet users have extra options and control based on pen pressure (in Photoshop only).

Liquify works by projecting the picture onto a grid or mesh (1). In an unaltered state, the grid is completely regular; when liquifying a photo the grid lines and spaces are intentionally distorted, which in turn causes the picture to distort. As the mesh used to liquify a photo can be saved and reloaded, the distortion effects created in one picture can also be applied to an entirely different image.

The tools contained in the filter’s toolbox are used to manipulate the underlying mesh and therefore distort the picture. Areas of the picture can be isolated from changes by applying a freeze mask to the picture part with the Freeze Mask tool.

Whilst working inside the filter dialog it is possible to selectively reverse any changes made to the photo by applying the Reconstruct tool. When applied to the surface of the image the distorted picture parts are gradually altered back to their original state (the mesh is returned to its regular form). Like the other tool options in the filter, the size of the area affected by the tool is based on the Brush Size setting and the strength of the change is determined by the Brush Pressure value.

New brushes can be added into the Brush Preset palette (Brush tool’s options bar) by pressing the sideways button at the top of the dialog and then selecting the Load Brushes item from the pop-up menu.

The feature opens a file browser dialog so that you can search for ABR or Adobe Brush files to load. Photoshop includes a range of predefined brush sets, or ABR files, that can be loaded from the Photoshop/ Presets/Brushes folder.

Alternatively you can download and install extra brush tips from resource sites on the internet or create and save your own brush sets using the Edit > Define Brush from Selection feature and the settings in the tool’s option bar.

Photoshop ships with a variety of gradient styles which are displayed in the Gradient Preset palette (Gradient tool’s options bar). New gradients can be added into the Preset palette by pressing the sideways button at the top of the dialog and then selecting the Load Gradients item from the pop-up menu.The feature opens a file browser dialog so that you can search for GRD or Adobe Gradient files to load. Those GRD files included in Photoshop can be loaded from the Photoshop/Presets/Gradients folder. Alternatively you can create and save your own gradients using the Gradient Editor.

A variety of patterns is preloaded in the Photoshop program when it is shipped. New options can be added into the Pattern Preset palette (Pattern Stamp tool’s options bar) by pressing the sideways button at the top of the dialog and then selecting the Load Patterns item from the pop-up menu. The feature opens a file browser dialog so that you can search for PAT or Adobe Pattern files to load. Those PAT files included in Photoshop can be loaded from the Photoshop/Presets/Patterns folder. Alternatively you can create and save your own patterns using the Edit > Define Pattern from a selection feature. Patterns can be used with the Paint Bucket tool and are also located as an option in the Fill Layer dialog box.

Photoshop thankfully gives you the option to save complex selections so that they can be used again later.

With your selection active choose the Save Selection option (1) from the Select menu. Your selection will now be saved as part of the file.

When you close your file and then open it again later you can retrieve the selection by choosing Load Selection from the same menu.

This feature is particularly useful when making sophisticated multi-step selections, as you can make sequential saves, marking your progress and ensuring that you never lose your work.

The Save Selection dialog also provides you with another way to modify your selections. Here you will find the option to save a newly created selection in any of the four selection modes (2). This provides you with an alternative method for building complex selections which is based on making a selection and then saving it as an addition. In this way you can create a sophisticated selection one step at a time.

A variety of color swatch palettes are supplied with Photoshop. A default set is the preloaded Swatches palette. Other swatch options - custom colors you have created or downloaded from the web - can be loaded into the palette by pressing the sideways button at the top of the dialog and then selecting the Load Swatches item (1) from the pop-up menu. The feature opens a file browser dialog so that you can search for ACO (Swatch) or ACT (Color Table) files to load. Swatch files are generally stored in the Photoshop/ Presets/Color Swatches folder.

Other industry-based color swatch sets ( 2 ) are also listed in the menu and can be added to the current list by selecting and appending the Swatch list.

Photoshop provides the option to lock layers so that their transparency, pixels or position cannot be changed.

This option is great for fixing the current editing state of a layer so that neither its content nor its position are changed by subsequent enhancement steps.

The Lock All button located at the top of the Layers palette locks and unlocks selected layers (1). A Locked padlock icon is displayed on the right-hand end of all locked layers (2). A dark shaded padlock indicates that the layer has been locked with the Lock All button.

To lock a layer, select the layer and click on the Lock All button at the top of the Layers palette. The shaded padlock will be displayed.

To unlock a locked layer, select the layer and then press the Lock All button. The shaded padlock will be removed from the right end of the selected layer.

As well as the option to lock all the attributes of a layer, Photoshop also provides an option to lock the transparent parts (1), pixels (2) and/or position (3) of a layer.

Use the Lock Transparent option to ensure that editing changes do not alter, or impinge upon, the transparent part of the layer.

The Lock Image Pixels feature ensures that no editing can take place in the image parts of a layer. Use this lock to protect layer content from inadvertent changes during the editing process.

The third option, Lock Position , stops the layer content from being moved. This option doesn’t protect the layer from being edited.

To lock the transparency of a layer, select the layer and click on the Lock button of your choice at the top of the Layers palette. The lightly shaded padlock will be displayed

(4). To unlock a layer with its transparency locked, select the layer and then press the same Lock button. The lightly shaded padlock will be removed from the right end of the selected layer.

Lossless compression is an approach to reducing the size of picture files that does not lose any image details or quality in the process. The same details are present in pictures after compressing and decompressing as were present in the original file.

At best the lossless approach produces compressed files that are half their original size. Some file formats such as JPEG2000 have options for both lossless and lossy compression ( 1 ).

A lossless file format should always be used to save original photos and artwork.

Common file formats that use lossless compression are:

• • TIFF (available in uncompressed and compressed lossless forms)
• • PNG
• • GIF (only supports 256 colors)
• • JPEG2000
• • DNG supports lossless compression of Raw file information

Lossy compression is an approach to reducing the size of picture files that discards image details and reduces photo quality in the process of creating smaller files.

The Save dialogs for file formats that use this method of compression generally contain a slider control that adjusts picture quality and file compression ( 1 ).

In general terms, the better the picture quality the larger the files (less compression) will be and, conversely, the smaller the file size (most compression) the worse the resultant image quality.

The Photoshop Save for Web feature contains a visual before and after preview of the results of differing levels of lossy JPEG compression. This provides the opportunity to preview the visual results of the compression to ensure that the degree of quality loss is acceptable.

Picture files can be dramatically reduced in size using lossy compression algorithms, which makes this approach most suitable for shrinking files for internet work or file transmission. Lossy file formats should not be used as primary archival format. Common file formats that use lossy compression are:

• • JPEG
• • JPEG2000 (has lossy and lossless options)
• • Photoshop PDF (JPEG option)
• • Photoshop TIFF (JPEG option)

The Luminosity blending mode is one of the group of Hue modes that base their effects on combining the hue, saturation and luminosity of the two layers.

This option creates the result by combining the hue and saturation of the bottom layer with the luminosity of the top layer.

The final image is the inverse of the results obtained when the Color mode is selected.

LZW or Lempel-Ziv-Welch compression is a lossless compression algorithm used to shrink the size of picture files by recognizing repeating patterns in the picture and only storing these once.

The algorithm is commonly used in the GIF format and is an option when saving TIFF files (1). Though LZW doesn’t reduce file sizes as small as JPEG, it does have the advantage of not losing any of the original data in the compression process.