Using blend modes on clips in Video by Zaweba

Blend modes decide how one clip's pixels mix with the pixels on the tracks underneath it. Normally the top clip simply covers what is below, but a blend mode changes the sum, so a clip can darken, lighten, add contrast or pass on only its colour. Video by Zaweba has all 26 of the standard blend modes, set per clip, and it works them out with the W3C compositing formulas, the same maths that web browsers and many design tools use. A clip blended in the editor therefore behaves the way you would expect from other software you know.

Because the setting belongs to the clip, you can stack several layers on different tracks and give each its own mode. One overlay can lighten, the next can add contrast, and a third can tint, all over the same piece of footage.

The modes worth learning first

You don't need to know all 26 to get good results. Multiply darkens: white in the top clip disappears and dark areas press down onto the picture below. It suits paper textures, shadows and anything printed on a white background. Screen does the opposite. Black disappears and bright areas glow through, which is why light leaks, lens flares, dust and fire footage shot on black are usually set to screen.

Overlay and soft light add contrast while keeping the base picture in charge. They work well for texture layers and for gentle grading tricks, where a coloured clip on top shifts the mood without hiding detail. Soft light is the quieter of the two. Colour dodge brightens hard and can blow out quickly, so keep it for small glows.

The component modes, hue and luminosity among them, split a picture into its parts. Luminosity takes only the brightness of the top clip, and hue takes only its hue, so you can borrow the colour of one shot or the tones of another. Those are handy when two clips need to feel related.

Putting a blend on a clip

Put the clip that should do the mixing on a higher track, select it and choose its blend mode in the Inspector. The Effects tab also lists blend modes alongside effects, transitions and graphics, with a search box, so you can find one by name if you prefer browsing. Play the section back in the preview, because some modes look very different on moving footage than on a single frame.

Opacity still applies on top of the blend. A screen layer at full strength may be too much, and pulling the opacity down is usually a better fix than changing to another mode. Both can be keyframed in Video by Zaweba, so a texture can fade up over a title or a flare can swell for a moment and go.

How blends fit with the rest of the app

Blend modes are one part of the compositing tools. Masks let you limit an overlay to part of the frame. An adjustment layer from Graphics changes everything on the tracks below it, which is a different job: it applies a grade or effect, where a blend mode mixes the picture of one clip into another. You will often use both together, perhaps a grain clip on screen or overlay for texture with an adjustment layer above it for the final look.

The colour tools also sit on each clip, so you can grade an overlay before it blends. Warming a light leak or lowering the saturation of a texture often matters more than which mode you picked.

Mistakes that cause a muddy result

The most common one is putting the blend mode on the wrong clip. The mode belongs to the upper clip, the one doing the mixing, not to the footage underneath. If nothing changes when you switch modes, check which clip is selected.

Another is stacking too many lightening or darkening layers. Each multiply darkens further and each screen lifts further, and before long the shadows are crushed or the highlights are a flat grey. Look at the scopes from the View menu if you are unsure, since the waveform shows clipping plainly.

Finally, remember that a blend on a clip with black or white bars, or with a logo on a solid background, blends the bars and the background too. Crop or mask the overlay first so only the part you want takes part in the mix.

Used lightly, blend modes are one of the quickest ways in Video by Zaweba to add texture and atmosphere without any extra effects at all.