Turn one line of a photo into streaks. The effect samples a row or a column, then writes that line over every pixel from there to the edge, so colours smear in straight bands. It is the look behind the stretched-portrait posters and the smeared product backgrounds, and it takes two settings to get there: where the line is and which way it runs.
Line position and direction
Line position is a share of the picture along the stretch axis: with Direction set to Down or Up it is a row, with Right or Left it is a column. The Up and down and Left and right options stretch from the line in both directions at once, which leaves a thin band of the original and smears everything else.
A portrait usually wants the line just below the face and the direction Down. A product on a plain background wants the line through the product’s base, so the streaks pick up its colours rather than the backdrop.
Band
At 0 the streaks come from a single line. That is the sharpest result, and on a busy line it produces thin stripes of every colour that crossed it. Raising Band to 2 or 3 percent averages the lines around it first, so the stripes widen and soften. Beyond 10 percent the streaks turn into broad gradients.
Stretch length
Stretch length stops the streaks short of the edge; at 100 they reach it. A shorter streak fades back into the original picture over its last quarter instead of ending on a hard line, which is how to stretch the middle of a photo without wiping out the edge.
Jitter
Jitter varies each streak’s start point and length at random. Low values break the hard line where the stretch begins; high values make the streaks ragged, like a wind filter. The arrangement is fixed, and because every distance is a share of the picture, the export at full size matches the preview.
Where it stops
The effect copies pixels; it does not blur or interpolate between them, so the streaks are as sharp as the source line. A smoother smear wants a small Band, or a motion blur afterwards in the image workflow.