ICDL Image Editing (ICDL) flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Raster image

An image built from a rectangular grid of pixels, each holding a colour value. Its quality depends on fixed pixel dimensions, so enlarging it beyond that size makes edges appear blocky or pixelated.

Vector image

An image defined by mathematical points, lines and curves rather than pixels. It can be scaled to any size or printed at any resolution without losing sharpness or showing pixelation.

Colour depth

The number of bits used to store the colour of each pixel. Eight bits give 256 levels per channel, and 24-bit RGB provides about 16.7 million possible colours.

PPI versus DPI

PPI counts image pixels per inch and determines print size from pixel dimensions. DPI counts printer ink dots per inch and describes device output, so the two terms are not interchangeable.

Lossy compression

A compression method that permanently discards some image data to shrink file size. JPEG is the common example, and repeated saving progressively degrades edges and fine detail.

Aspect ratio

The proportional relationship between an image's width and height, written as two figures such as 4:3 or 16:9. Changing it without cropping stretches or squashes the picture.

RGB and CMYK

RGB is an additive colour model mixing red, green and blue light, used for screens. CMYK is subtractive, mixing cyan, magenta, yellow and black inks for print output.

Optical zoom

Zoom produced by physically changing the camera lens focal length. It magnifies the scene using the full sensor resolution, so image detail and sharpness are preserved.

Digital zoom

Zoom produced by cropping the sensor image and enlarging the remaining pixels through interpolation. It reduces effective resolution and usually gives softer, noisier results than optical zoom.

EXIF metadata

Data automatically written into a photo file by the camera, recording settings and context such as shutter speed, aperture, ISO, date, camera model and sometimes location coordinates.

Scanner resolution setting

The pixels per inch value chosen when scanning. Scanning at 300 ppi suits printing at original size, while enlarging the print requires a proportionally higher scanning setting.

RAW file format

A minimally processed camera file that retains sensor data without in-camera sharpening or strong compression. It gives the greatest editing latitude but must be converted for general use.

TWAIN driver

Software that lets an image-editing program communicate directly with a scanner or camera. Selecting the TWAIN or WIA source opens the device's own capture interface.

Cropping

Removing the outer parts of an image to change its framing or aspect ratio. Cropping deletes those pixels and reduces overall pixel dimensions rather than scaling the content.

Resampling

Changing the number of pixels in an image by interpolation. Downsampling removes pixels; upsampling invents new ones from neighbours, softening detail without restoring missing information.

Histogram

A graph showing how many pixels sit at each brightness level, with shadows on the left and highlights on the right. It reveals clipping and tonal bias without altering the image.

Levels adjustment

A tonal control that sets new black, midtone and white points. Moving the sliders darkens shadows, brightens highlights or changes midtone brightness and overall contrast.

Feathering a selection

Softening a selection edge so edits fade gradually into surrounding pixels. A feathered edge prevents a hard visible line when deleting, filling or pasting inside the selection.

Clone stamp tool

A retouching tool that paints with pixels copied from a sample point you set elsewhere in the image. It removes blemishes, dust marks and small unwanted objects.

Layer mask

A greyscale channel attached to a layer that controls where that layer shows. Black hides, white reveals and grey produces partial transparency, allowing non-destructive editing.

Layer blending mode

A setting determining how a layer's pixels combine with the pixels beneath it. Multiply darkens, Screen lightens and Normal simply covers the layers below.

Canvas size

The dimensions of the working area, changed without scaling existing content. Enlarging adds empty space around the image; reducing it crops or hides content near the edges.

Free transform

A command that scales, rotates, skews, distorts or flips a selected layer or selection. Holding the shift key while dragging a handle usually constrains proportions.

Batch processing

Applying the same action, such as resizing, renaming or format conversion, automatically to many files in one run. It saves repetitive work when preparing large groups of images.

Image catalogue keywords

Descriptive tags stored in image metadata by photo-management software. They make files searchable by subject, so pictures can be found without relying on filenames or folders.

Panorama stitching

Software combines several overlapping photographs into one wide image by matching shared features and blending the joins. Frames must overlap substantially and share consistent exposure.

Soft proofing

Simulating on screen how an image will appear when printed with a particular ink, paper and printer profile. It previews colour shifts before committing to final output.

PNG transparency

PNG supports an alpha channel, so parts of an image can be fully or partly transparent. It is lossless and suits logos and graphics placed over coloured backgrounds.

Output sharpening

A sharpening pass applied after an image is resized to its final output dimensions, compensating for softness introduced by resampling and by printing or display.

sRGB colour space

A standard colour space covering the range typical of consumer monitors and the web. Images exported for screen viewing are normally converted to sRGB for consistent colour.

Print size formula

Divide the image pixel width and height by the intended output PPI. A 3000-pixel-wide image printed at 300 ppi produces a print 10 inches wide.

Bleed area

Extra image area extending beyond the trimmed edge of a printed page. It prevents white slivers appearing if the cutting drifts slightly during trimming.