Common Photoshop Terms Glossary

When you first start using Photoshop, it can seem like it is full of strange terms like Aliasing, Dithering and Gamut. Learning what these terms mean takes time, making this glossary of Photoshop terms a very handy time-saver!

Photoshop – A list of terms you may encounter as you learn

Active layer

The layer currently selected in the Layers panel.

Adjustment layer

A layer that lets you apply colour and tonal adjustments to your image without permanently changing pixel values. Use adjustment layers to experiment with colour and colour tones. You can think of an adjustment layer as a veil through which the underlying layers are seen.

Adobe RGB

The RGB colour space profile created by Adobe Systems, Incorporated. It provides a large gamut of colours. (See also RGB.)


The jagged edges seen at the edges of diagonal lines, arcs, and so on, caused by pixels lining up in a saw-tooth pattern.

Alpha channels

Masks, which let you manipulate, isolate, and protect specific parts of an image. In Photoshop, alpha channels are called saved selections. To save an alpha channel, choose Select > Save Selection. To load an alpha channel, choose Select > Load Selection.


The smoothing of jagged edges in digital images by averaging the colours of the pixels at a boundary.
Artefact Any unexpected and undesired change to a digital image caused by incorrect settings or faulty processing. Examples include blooming, moiré, sharpening, and noise.

Aspect ratio

The ratio of an image’s width to its height. It is used to determine how an image fits on a page or monitor.

Background layer

The bottom-most layer in an image, usually containing the image data. The Background layer is always locked. If you want to change its stacking order, blending mode, or opacity, you must first convert it to a regular layer.


Light coming from a source behind the subject.

Batch processing

Performing one or more tasks to a group of files at the same time.

Bit depth

The number of colours used to represent a pixel in an image. A 1‑bit image is black and white; an 8‑bit image can have 256 colours or shades of grey; a 16‑bit image can have 65,536 colours.

Bitmap image

An image consisting of rows and columns of pixels in computer memory. Also called a raster image. Bitmap file formats include BMP, GIF, JPEG, PSD, PICT, and TIFF. (See also vector graphics.)

Bits per channel

Determines how many tones each colour channel can contain.

Blending mode

A feature that controls how pixels in an image are affected by a painting or editing tool. The blend colour is applied to the base (original) colour to produce a new colour.

Brush preset

A brush with preset settings for size, thickness and so on. Photoshop includes several brush presets for you to choose from, and you can create a large number of your own presets as well.


The selective darkening of a part of an image.

Camera raw format

A format describing data exactly as it is captured by a camera sensor, with no in‑camera processing applied to the capture.


The workspace around an existing image, within the image window. Layer data may lie outside of the canvas, but it will be clipped to the canvas when the image is flattened. You can change the size and colour of the canvas by choosing Image > Resize > Canvas Size.


A construct for describing the colour data in an image. A black-and-white greyscale image has one channel, an RGB image has three, and a CMYK image has four.


The temporary holding area for data stored with the Cut or Copy commands.


To paint with the Clone Stamp tool. You must set a sampling point on the active layer before you paint with the Clone Stamp tool.


Cyan, magenta, yellow, and black; the inks most printers use to produce colour images. Photoshop includes full support for CMYK mode.

Colour cast

An unwanted or unexpected colour shift in a photo. For example, a photo taken indoors without a camera flash may have too much yellow.

Colour channels

The component colours from which all colours in an image are created. Usually refers to red, green, and blue (RGB).

Colour depth

Measures how much colour information is available to display or print each pixel in an image. Greater colour depth means more available colours and more accurate colour representation in the digital image.

Colour management

A system used to achieve consistent colour as an image travels from one device to another.

Colour temperature

The degree of heat (in degrees Kelvin) that an object would have to absorb before it glowed in a certain colour. Each colour is associated with a colour temperature, as are various kinds of light.


A technique that reduces the file size of bitmap images.


Trimming a portion of an image to improve its composition or to create a frame around it.


Sharpness or clarity of detail in an image.


The approximation of an unavailable colour through the use of two or more available colours. The colour of adjacent pixels is changed in an attempt to reproduce the unavailable colour.


The selective lightening of any part of an image.

Dots per inch (dpi)

A measure of printer resolution. High dpi settings produce prints with fine detail. Also used for monitors. (See also pixels per inch (ppi).)


A two‑colour greyscale file that uses two custom inks.

Embedded profile

An ICC (colour) profile resident in an image file. This profile ensures that image colours are correctly interpreted.


Encapsulated PostScript. A file format used to save images that will be used in illustration and pagelayout programs.


Exchangeable Image File Format. A standard for simplifying the exchange of data between cameras and software. The data may include camera model, date and time the photo was taken, camera settings, shutter speed, and so on.


A measure of the amount of light in which a photo was taken. Underexposed digital photos are too dark; overexposed ones, too light.


The softening of an edge of a selection.

Fill layer

A type of layer that contains a solid colour, a pattern, or a gradient as an interchangeable attribute. (See also layer and adjustment layer).


Options to alter the look of an image, for instance, to make it look like a mosaic, add unique lighting, apply distortions, and so on.


Merging all visible layers into the Background layer to reduce file size.


A set of letters, numbers, punctuation marks, and symbols that share a common weight, width, and style.

48‑bit RGB colour

A high‑bit image mode that can contain thousands of colours per channel. Photoshop supports 8‑bit or 16‑bits per colour channel, so an RGB image can be a total of 24‑bit or 48‑bit, depending on the bit depth per channel.

Gamma adjustment

The contrast resulting from darkening or lightening the mid-tones of an image.


The range of colour that a device can reproduce.

Gaussian blur

A softening effect applied through a bell-shaped distribution of tones and colours.


Graphic Image File Format. A file format suitable for images that contain line art, large areas of a single colour, and text. Web animations are done with images in GIF format.


Any of several methods for achieving a smooth transition between two adjacent colours, including black and white.


A single-channel image that includes only black, white, and shades of grey. Depending on the bit depth, greyscale images can reproduce various shades of grey.


A monochrome image made up of variably sized dots simulating the shades of grey in a photograph. It is used for reproducing photographs on PostScript printers and printing presses.

Highlight and shadow

The lightest and darkest colours in an image.


A bar chart showing the distribution of the pixel values in a digital image.


The colour reflected from or transmitted through an object. In common use, hue is the property that allows a colour to be distinguished as red, blue, yellow, and so on.


International Colour Consortium. ICC device profiles are the industry standard for reproducing colours accurately across devices such as scanners, monitors, and printers.

Image cache

A section of hard disk space used as virtual memory. The image cache speeds the on‑screen redraw of high-resolution images.

Image mode

The colour mode of an image, such as Greyscale or RGB.

Indexed colour

A colour that is rendered by using a pixel value as an index to a panel of 256 or fewer colours.


Joint Photographic Experts Group. A committee of experts that develops algorithms for compressing computer image files. Also, any graphic file to which a JPEG algorithm is applied. JPEG is the format generally used to share photographs over the web.

JPEG compression

A lossy compression technique that reduces image data and file size.


A mechanism for overlaying and combining multiple images. Layers are like transparent sheets of glass that you can stack and rearrange.

Layer group

A collection of layers saved with a Photoshop image.

Layer mask

A protected area in an adjustment layer. Areas below the mask cannot be edited.


Functionality for adjusting colour and tone. With a Levels adjustment, you can set shadow and highlight values to use a full tonal range, adjust middle tones only, correct colour casts, and so on.

Locked layer

A layer in the Layers panel that has the lock icon applied. No changes can be made to a locked layer. A Background layer is always locked.

Lossless compression

An image-compression technique that prevents image degradation caused by data loss. Lossless techniques usually use lower compression ratios than lossy techniques.

Lossy compression

An image-compression technique using compression ratios that result in the loss of some image data.


A method for simulating transparency in images displayed on web pages. When transparency is not supported, you can specify a matte colour that matches the background to simulate transparency.


An area that falls between the brightest highlight and the darkest shadow.


A wavy striped pattern in an image, resembling the pattern of watered silk. Moiré can be an artefact caused by a camera’s inability to capture the detail in an image.

Monitor resolution

The resolution of a monitor, described in pixel dimensions. The size of an image displayed on‑screen depends on the pixel dimensions of the image, the size of the monitor, and the monitor resolution.


An artefact caused by interference or camera error. Noise is often seen as stray pixels of unexpected colour or a generally “grainy” appearance. Certain compression techniques can amplify noise.


The extent to which something blocks light. You can change the opacity of layers, filters, and effects so that more (or less) of the underlying image shows through.


A broad view of a subject, usually a landscape, made by overlapping individual shots as they are taken and then merging them to form one image.


Portable Document Format. An Adobe file format that captures the elements of a printed document, including graphics and photos, as an electronic image. You can search, navigate, print, and e‑mail PDF documents.


The angle or level from which a photograph is taken; the camera-eye view.


The basic, rectangular unit of data that a digital image consists of. The edges of pixels can produce a saw-tooth pattern unless anti-aliasing is used.

Pixel dimensions

The number of pixels along the width and height of an image. This is a measure of the amount of image data in the photo, not its physical size when printed or displayed on a monitor.

Pixels per inch (ppi)

A measure of image resolution stored in a camera or computer file. High ppi settings produce photographs with fine detail and large file size. (See also dots per inch (dpi).)


A language developed by Adobe that describes the appearance of text, graphic shapes, and sampled images on printed or displayed pages.

Printer profiles

Profiles that describe how printers reproduce colours.

Progressive scan

A process of displaying images on‑screen that draws 60 complete frames of video from left to right every second. Progressive scan creates a cleaner, clearer picture than interlaced video.


The native uncompressed file format of Adobe Photoshop, based on the TIFF standard.

Quick mask

A mask channel created in Quick Mask mode.

Red eye

The reflection of the camera flash from the retina of a photographed subject, resulting in a red dot in the subject’s eye. You can eliminate it automatically when you import images or by using the Red Eye
Removal tool.


Converting a vector layer such as a shape layer or a text layer into a normal layer.


To change the resolution of an image by changing its pixel dimensions. Downsampling is decreasing the number of pixels, and resampling up (or upsampling) is increasing the number.


A measure of the clarity and sharpness of an image. In digital images, it is measured in pixels per inch.


A model for representing colours on a computer display. Red, green, and blue (RGB) are combined in different proportions to represent any colour. The RGB model can represent 256 x 256 x 256 colours.


To select a colour with the eyedropper in order to use it with a drawing or painting tool.


The purity, or strength, of a colour. A fully saturated colour contains no grey. Saturation controls make colours more vivid (less black or white added) or more muted (more black or white added).


A part of an image selected for manipulation of any kind, duplication in a layer, colour correction, deletion, rotation, and so on. The selection consists of all the pixels, fully or partially selected, contained within the selection boundary.


In photo-editing programs, any functionality that enhances the details at the edges of photographed objects and people. Sharpening is often applied as part of in‑camera processing as well, although no sharpening is applied to camera raw file images.


Deviation of the content of an image from a vertical or horizontal axis. Skewing can be a camera artefact or an intentionally applied effect.


A technique for averaging the values of neighbouring pixels to reduce contrast and create a soft, blurry effect.


(1) An outline around an image or part of an image created with the Stroke command or with a drawing, painting, or selection tool. (2) The characteristics of the lines created with one of the painting or drawing tools, especially brushes.


Preset colours that you can choose from in the Colour Swatches panel.


Tagged Image File Format. A digital image format widely used for images that are to be printed or published. TIFF images can be compressed losslessly.


To scale, shrink, enlarge, skew, distort, rotate, or change the perspective of a layer, selection, or shape.


In digital photography, the functionality that supports transparent areas in an image or image layer. Certain image formats do not support transparency.

Unsharp mask

A technique that sharpens details in an image by increasing the contrast between light and dark areas. (The name originates from traditional photography, where contrast is increased by adding a slightly blurred negative over the original.)

Vector graphics

Lines, shapes, and other graphic image components stored in a format that incorporates geometric formulas for rendering the image elements. For this reason, the graphics scale without degradation of image quality, and there are no jagged lines in the output. Adobe Illustrator is a vector graphics program.

Vignette, Vignetting

A darkening of the edges of an image.


A distortion of an image, often text, to conform to a variety of shapes. For instance, a line of text can be warped in the shape of an arc or wave.

White balance

A function that compensates for the different rendering of identical colours under different sources of light: incandescent, fluorescent, sunlight, and so on.

White point

A reference point used to represent white. This reference point is used to calculate all other colours in the image.

Russ Ware

Russ has been testing, reviewing and writing guides for tech since the heady days of Windows 95 and the Sega Saturn. A self-confessed (and proud) geek about all things tech, if it has LED's, a screen, beeps or has source code, Russ will want to master it (and very likely take it apart to see how it works...)

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