ICDL Image Editing (ICDL) cheat sheet

Raster (bitmap) images are grids of pixels; vector images are mathematical paths and scale without any loss of sharpness.

Print size in inches = pixel dimension ÷ PPI (for example 2400 px ÷ 300 ppi = 8 in).

Uncompressed file size in bytes ≈ width × height × (bit depth ÷ 8); a 24-bit 1000 × 1000 px image is about 3 MB.

Colour depth: 1-bit = 2 colours, 8-bit = 256 levels per channel, 24-bit RGB = 16 777 216 possible colours.

RGB is an additive model used for screens and projectors; CMYK is a subtractive ink model used for commercial print.

JPEG compression is lossy; PNG, GIF and TIFF are lossless formats, so repeated JPEG re-saving accumulates visible artefacts.

Aspect ratio is width:height (common values 4:3, 3:2, 16:9); changing it without cropping stretches or squashes the picture.

300 ppi is the conventional print standard; 72–96 ppi matches typical on-screen display density.

PPI counts image pixels per inch and sets print size; DPI counts printer ink dots per inch and describes the output device.

Optical zoom changes the lens focal length and keeps full sensor resolution; digital zoom crops and interpolates, lowering effective resolution.

Doubling scanner ppi doubles each linear dimension, so the total pixel count and file size increase fourfold.

Required scan ppi = target print ppi × (final print size ÷ original document size).

RAW keeps unprocessed sensor data for maximum editing latitude; JPEG applies in-camera processing and lossy compression.

EXIF metadata stored in the file records camera model, date and time, shutter speed, aperture, ISO and often GPS coordinates.

Scanners and cameras are acquired through TWAIN or WIA drivers, card readers, USB cables or wireless transfer.

Camera resolution is quoted in megapixels, where 1 MP is approximately 1 000 000 pixels of the recorded image.

Screenshots, scanned documents, stock libraries, downloaded web graphics and camera files are all valid acquisition sources; confirm the licence before reuse.

Cropping deletes pixels outside a chosen area and reduces pixel dimensions; resizing resamples the entire image content.

Lock or constrain proportions when resizing so the aspect ratio stays fixed and the image is not distorted.

On a histogram, shadows sit on the left, midtones in the centre and highlights on the right; data touching either end is clipped.

Brightness shifts all tones together; contrast expands or compresses the tonal distance between shadows and highlights.

Levels sets input black, gamma and white points; Curves maps input tones to output tones along an adjustable line.

Main selection tools: marquee for fixed shapes, lasso for freehand outlines, magic wand for colour similarity, quick selection for edge-aware brushing.

Feathering softens a selection border so edits fade into neighbouring pixels instead of leaving a hard visible line.

Bicubic resampling suits photographs; nearest-neighbour resampling preserves hard edges in graphics and pixel art.

Layers combined with layer masks allow non-destructive editing; erasing or applying destructive filters changes pixels permanently.

Layer order sets the stacking: an upper layer covers those below unless opacity or a blending mode alters the result.

Canvas size changes the working area without scaling content; image size resamples the content itself.

Blending modes: Multiply darkens, Screen lightens, Overlay boosts contrast, Normal simply covers the layers beneath.

Free transform applies scale, rotate, skew, distort and flip; constrained dragging of a corner handle preserves proportions.

Paste Into (paste inside a selection) confines the pasted content to a layer mask built from the selection.

Panorama stitching needs roughly 20–30% overlap between frames plus consistent exposure across the sequence.

Organise with folders, meaningful filenames, keywords, star ratings and captions so files remain searchable in a catalogue.

Batch commands apply renaming, resizing or format conversion to an entire folder in a single run.

Output print size = pixel dimensions ÷ chosen PPI; increasing PPI shrinks the printed size while pixel dimensions stay unchanged.

Work in RGB and convert to CMYK only at final output for commercial print.

Format choice: JPEG for photographs and web, PNG for transparency and lossless graphics, GIF for simple animation, TIFF for print archiving, SVG for vector artwork.

JPEG quality settings around 60–80 balance small file size against visible compression artefacts for web delivery.

Export screen images in the sRGB colour space, resized to the exact display pixel dimensions required.

Apply output sharpening after the final resize; over-sharpening produces visible halos along high-contrast edges.

Print layouts include bleed (commonly 2–3 mm) beyond the trim edge, with text kept inside safe margins.

Transparency support: PNG carries a full alpha channel, GIF supports one fully transparent colour, JPEG supports none.

Soft proofing simulates a printer and paper profile on screen so colour shifts can be judged before output.