### 4.8. Markeringsredigering

Kommandoen Markeringsredigering viser dialogvinduet “Markeringsredigering”. Dette dialogvindue viser den aktive markering i det aktuelle billede og giver dig nem adgang til de markeringsrelaterede kommandoer. Det er egentlig ikke beregnet til at redigere markeringer direkte, men hvis du arbejder på en markering, er det praktisk at have markeringskommandoerne samlet, da det er nemmere at klikke på en knap end at søge efter kommandoer i kommandotræet på menulinjen. “Markeringsredigering” tilbyder også nogle avancerede muligheder for kommandoen “Markering til kurve”.

#### 4.8.1. Aktivering af kommandoen

Du kan tilgå denne kommando i hovedmenuen via Markering → Markeringsredigering.

#### 4.8.2. Beskrivelse af dialogvinduet “Markeringsredigering”

Figur 16.19. Dialogvinduet “Markeringsredigering”

Knapperne

  Dialogvinduet “Markeringsredigering” har flere knapper, som giver nem adgang til markeringskommandoer:

  - Knappen Markér alt.

  - Knappen Markér intet.

  - Knappen Invertér markeringen.

  - Knappen Gem som kanal.

  - Knappen Til kurve. Hvis du holder Skift nede, mens du klikker på denne knap, vises dialogen Avancerede indstillinger. Se næste afsnit for detaljer om disse indstillinger.

  - Knappen Optegn markering.

Visningsvinduet

  I visningsvinduet er markerede områder af billedet hvide, ikkemarkerede områder er sorte, og delvist markerede områder er i gråtoner. At klikke i dette vindue fungerer som Markering efter farve. Se eksemplet nedenfor.

Figur 16.20. Eksempel på klik i visningsvinduet for “Markeringsredigering”

Markeringsredigeringsvinduet efter der er klikket.

Billede med den resulterende markering anvendt.

#### 4.8.3. Dialogen “Avancerede indstillinger for markering til kurve”

Figur 16.21. Dialogvinduet “Avancerede indstillinger”

Dialogen “Avancerede indstillinger for markering til kurve”, som du får ved at klikke på knappen Markering til kurve, mens Skift holdes nede, indeholder en række indstillinger, hvoraf de fleste kan indstilles med enten en skyder eller en tekstboks. Der er også et afkrydsningsfelt. Disse indstillinger bruges mest af avancerede brugere. De er følgende:

Align Threshold

  If two endpoints are closer than this value, they are made to be equal.

Corner Always Threshold

  If the angle defined by a point and its predecessors and successors is smaller than this, it is a corner, even if it is within Corner Surround pixels of a point with a smaller angle.

Corner Surround

  Number of points to consider when determining if a point is a corner or not.

Corner Threshold

  If a point, its predecessors, and its successors define an angle smaller than this, it is a corner.

Error Threshold

  Amount of error at which a fitted spline[6] is unacceptable. If any pixel is further away than this from the fitted curve, the algorithm tries again.

Filter Alternative Surround

  A second number of adjacent points to consider when filtering.

Filter Epsilon

  If the angles between the vectors produced by Filter Surround and Filter Alternative Surround points differ by more than this, use the one from Filter Alternative Surround.

Filter Iteration Count

  The number of times to smooth the original data points. Increasing this number dramatically, to 50 or so, can produce vastly better results. But if any points that “should” be corners aren't found, the curve goes wild around that point.

Filter Percent

  To produce the new point, use the old point plus this times the neighbors.

Filter Secondary Surround

  Number of adjacent points to consider if Filter Surround points defines a straight line.

Filter Surround

  Number of adjacent points to consider when filtering.

Keep Knees

  This check box says whether or not to remove “knee” points after finding the outline.

Line Reversion Threshold

  If a spline is closer to a straight line than this value, it remains a straight line, even if it would otherwise be changed back to a curve. This is weighted by the square of the curve length, to make shorter curves more likely to be reverted.

Line Threshold

  How many pixels (on the average) a spline can diverge from the line determined by its endpoints before it is changed to a straight line.

Reparametrize Improvement

  If reparameterization doesn't improve the fit by this much percent, the algorithm stops doing it.

Reparametrize Threshold

  Amount of error at which it is pointless to reparameterize. This happens, for example, when the algorithm is trying to fit the outline of the outside of an “O” with a single spline. The initial fit is not good enough for the Newton-Raphson iteration to improve it. It may be that it would be better to detect the cases where the algorithm didn't find any corners.

Subdivide Search

  Percentage of the curve away from the worst point to look for a better place to subdivide.

Subdivide Surround

  Number of points to consider when deciding whether a given point is a better place to subdivide.

Subdivide Threshold

  How many pixels a point can diverge from a straight line and still be considered a better place to subdivide.

Tangent Surround

  Number of points to look at on either side of a point when computing the approximation to the tangent at that point.

[6] “Spline” er en matematisk betegnelse for en funktion, der definerer en kurve ved hjælp af en række kontrolpunkter som f.eks. en Bézier-kurve.

Se Wikipedia eller Lex for flere oplysninger.

4.7. Markering fra kurver |  | 4.9. Udtynd

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