develops
would be standard English answers (not technical)

"...edge of picture gradually morphs into another" - it´s modern English. "Morph" is used in a lot in computer graphics work, meaning to become transformed from one thing into another, thus in that context that a picture or graphic goes through a number of stages of transformation until ithas become another picture.

Previously it was in science fiction and other fantasy where a being of some kind transforms into another. I don´t think it has French origin, it certainly has a root in classical Greek. I don´t remember the actual word, I just know that the use of "morph" in this way seems perfectly natural to me.

could be used for this kind of gradual change.

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Note added at 14 mins (2003-11-29 16:48:12 GMT)
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blends in

Paradiso XXIII - [ Traduzca esta página ]
... who cannot find, 135 For all his thought, the principle he needs, Just so was I
on seeing this new vision I wanted to see how our image fuses Into the circle ...
www.italianstudies.org/comedy/Paradiso33.htm - 29k - En caché - Páginas similares

Introduction to Paradiso - [ Traduzca esta página ]
... Fascinated and drawn to this likeness of our features (nostra effige), Dante longs
to know how in "this new vision" our image fuses into "the circle and finds ...
www.italianstudies.org/comedy/Paradiso_int.htm - 35k - En caché - Páginas similares

Bundyology - An Article Early MwC - [ Traduzca esta página ]
... Al. But before the double image fuses into focus, the actor reaches
into his pocket and pulls out a prop of his own: dental floss. ...
www.bundyology.com/hanging.html - 38k - En caché - Páginas similares

Stereoptican - [ Traduzca esta página ]
... feet away. When you start to see a double image, slowly converge your
eyes until the middle picture fuses into one image. Slightly ...
www.eng.uci.edu/students/mpontius/ hartley/216x-216.html - 4k - En caché - Páginas similares



ANOTHER APPROACH IS TO GO TO www.thesaurus.com and enter verbs with similar meanings (such as I have done with fuse), so as to search for the word you need.
35 entries found for fuse.
Entry: fuse
Function: verb
Definition: meld
Synonyms: agglutinate, amalgamate, blend, cement, coalesce, combine, commingle, deliquesce, dissolve, federate, flux, integrate, interblend, interfuse, intermingle, intermix, join, liquefy, liquesce, melt, merge, mingle, run, run together, smelt, solder, thaw, unite, weld
Concept: joining physically
Source: Roget's Interactive Thesaurus, First Edition (v 1.0.0)
Copyright © 2003 by Lexico Publishing Group, LLC. All rights reserved.

Entry: alloy
Function: verb
Definition: mix
Synonyms: admix, amalgamate, blend, combine, compound, fuse, intermix, mix
Antonyms: clear, not mix, purify, separate
Concept: joining physically
Source: Roget's Interactive Thesaurus, First Edition (v 1.0.0)
Copyright © 2003 by Lexico Publishing Group, LLC. All rights reserved.

Entry: amalgamate
Function: verb
Definition: blend
Synonyms: admix, alloy, ally, coalesce, combine, come together, compound, consolidate, fuse, incorporate, integrate, interface, intermix, join together, meld, merge, mingle, network, pool, team up, tie in, tie up, unite
Antonyms: diffuse, disperse, divide, separate
Concept: joining physically
Source: Roget's Interactive Thesaurus, First Edition (v 1.0.0)
Copyright © 2003 by Lexico Publishing Group, LLC. All rights reserved.

Entry: ammunition
Function: noun
Definition: projectiles
Synonyms: armament, ball, bomb, buckshot, bullet, cannonball, cartridge, charge, chemical, confetti, explosive, fuse, grenade, gunpowder, iron rations, materiel, missile, munition, napalm, powder, rocket, round, shell, shot, shrapnel, torpedo
Concept: weapon
Source: Roget's Interactive Thesaurus, First Edition (v 1.0.0)
Copyright © 2003 by Lexico Publishing Group, LLC. All rights reserved.

Entry: blend
Function: verb
Definition: mix
Synonyms: amalgamate, cement, coalesce, combine, commingle, commix, compound, fuse, integrate, interblend, intermix, meld, merge, synthesize, unite, weld
Antonyms: divide, separate, unmix
Concept: joining physically
Source: Roget's Interactive Thesaurus, First Edition (v 1.0.0)
Copyright © 2003 by Lexico Publishing Group, LLC. All rights reserved.

Entry: bond
Function: verb
Definition: fasten
Synonyms: bind, connect, fix, fuse, glue, gum, paste, stickum
Antonyms: let go, loosen, open, unfasten, unstick
Concept: attachment
Source: Roget's Interactive Thesaurus, First Edition (v 1.0.0)
Copyright © 2003 by Lexico Publishing Group, LLC. All rights reserved.

Entry: cement
Function: verb
Definition: attach
Synonyms: bind, blend, bond, cohere, combine, connect, fasten, fuse, glue, gum, join, merge, mortar, paste, plaster, seal, solder, stick, unite, weld
Antonyms: divide, separate, unfix
Concept: attachment
Source: Roget's Interactive Thesaurus, First Edition (v 1.0.0)
Copyright © 2003 by Lexico Publishing Group, LLC. All rights reserved.

Entry: close
Function: verb
Definition: join
Synonyms: agree, bind, chain, coalesce, come together, connect, couple, encounter, face, front, fuse, grapple, inclose, meet, tie, unite
Antonyms: disjoin, divide, separate
Concept: joining physically
Source: Roget's Interactive Thesaurus, First Edition (v 1.0.0)
Copyright © 2003 by Lexico Publishing Group, LLC. All rights reserved.

Entry: coalesce
Function: verb
Definition: blend
Synonyms: adhere, amalgamate, associate, bracket, cleave, cling, cohere, combine, commingle, commix, conjoin, connect, consolidate, fraternize, fuse, incorporate, integrate, join, link, merge, mingle, mix, relate, stick, unite, wed
Antonyms: divide, fragment, separate, split
Concept: joining physically
Source: Roget's Interactive Thesaurus, First Edition (v 1.0.0)
Copyright © 2003 by Lexico Publishing Group, LLC. All rights reserved.

Entry: cohere
Function: verb
Definition: stick to
Synonyms: adhere, associate, bind, blend, cleave, cling, coalesce, combine, connect, consolidate, fuse, glue, hold, join, merge, unite
Antonyms: divide, fall off, separate
Concept: joining physically
Source: Roget's Interactive Thesaurus, First Edition (v 1.0.0)
Copyright © 2003 by Lexico Publishing Group, LLC. All rights reserved.

vignette maybe the word you are looking for but Im not sure you are using it correctly. A vignette is a small image with a decorative border, or in the context of things that have a time dimension (theatre / film) it describes short scenes.

vignette is used to describe decorative borders and filters, but the transformation of a decorative border, or the beginings and ends of a theatrical vignette is usually called a 'fade.'