Extend a photo to a new aspect ratio with Flux.1 Fill outpainting

SOURCE IMAGE AND MASK
storefront_original.jpg — a 4:5 photo of a café storefront, cropped tightly around the entrance, with the outpaint mask covering a strip added to both the left and right sides to convert the crop from 4:5 to a 16:9 banner — the new blank canvas area beyond the original frame's edges that Fill needs to generate.

WHAT THE ORIGINAL FRAME CONTAINS
the café's glass double door, a chalkboard sign, and one outdoor table, all in soft midday shade. This part of the image is fixed and must not be altered, recolored, or redrawn — Fill's job is only to generate the masked extension, not to touch the kept region.

WHAT SHOULD LOGICALLY CONTINUE INTO THE NEW AREA
the same brick facade continuing on both sides, with the neighboring shop's awning edge just visible entering frame on the right. Describe this as a continuation of the same physical scene, not a new scene bolted on — the same brick course lines and mortar color, and the same pavement level and curb height should carry the same light direction, the same lens perspective, and the same surface or material continuing believably past the original edge.

PERSPECTIVE AND SCALE MATCHING
The new region must obey the same vanishing points and scale established in the kept region. If a floor, horizon line, or receding surface is visible at the original edge, continue it at the same apparent rate rather than resetting perspective — a mismatched horizon is the most common visible tell that an outpaint was added rather than shot in-camera.

LIGHT AND COLOR CONTINUITY
identical soft midday shade with no direct sun anywhere in frame, matching the kept region's slightly cool color temperature. The extended area's exposure, color temperature, and grain should match the kept region exactly at the seam, fading only if the scene itself would naturally do so — for example, deeper shadow further from a window.

WHAT SHOULD NOT APPEAR IN THE NEW AREA
Since there is no negative-prompt field, state this positively instead: the extended region contains only the continuation content described above — no new subject, no text, no logo, no object that would draw more attention than what is already in the kept frame.

IF THE EXTENSION IS LARGE
When the masked area is wide relative to the kept region — extending a tight crop into a full billboard aspect ratio, for instance — treat the far edge of the new canvas with the same discipline as the seam itself: it should still look like a continuation of one believable physical space, not a second, looser guess once it's far enough from the original photograph to feel unconstrained. State explicitly whether any variation is acceptable that far out (a slight change in what's visible on a wall, for example) or whether it must remain just as tightly matched as the area right at the seam.

CHECK BEFORE FINALIZING
Look specifically at the exact boundary line between kept and generated pixels at full resolution — a faint value or color-temperature step at that line, even a subtle one, is the most common outpainting defect and is often only visible on close inspection rather than at a quick glance, which is exactly why it's worth checking deliberately rather than assuming a generally good result means the seam is clean too.

OUTPUT
One image at the full new 16:9 for a website hero banner canvas, with a seam between the original photograph and the generated extension that is not detectable on close inspection.