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Image.draw_* fail on images from Image.Read: pixel data is not C-contiguous (cv2 line/circle/putText layout error)

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Seit 21.10.2026.

  • #162 von @petercorke — offen

Bewertung

Schwierigkeit
3/5
Geschätzter Aufwand
1-2 Tage
Anfängerfreundlichkeit
35/100
Issue-Typ
Bug
Klarheit
Klar beschrieben
Aktivitätsstatus
Veraltet
Tech-Stack
opencv, python
Bereich
backend, computer-vision

Rechercherichtung

Start in base/graphics.py, where draw_point calls cv2.putText, and inspect the other draw_* functions that pass the image to OpenCV drawing calls. Reproduce with the issue's Image.Read("monalisa.png") example and check the array's contiguity; add the requested regression test for drawing text on an image read this way. Done when the drawing call succeeds on OpenCV 5 and the regression test passes; pull request #162 is already open.

Vom Indexierungsmodell aus dem Issue-Text verfasst.

Beschreibung

bug

On OpenCV 5.0, Image.draw_point(..., text) raises when the image comes straight from Image.Read. This breaks the example in its own docstring, so the published docs show a traceback.

Reproduce

OpenCV 5.0.0 (also 5.0.0.93 from PyPI), origin/main at 77a3da9c:

from machinevisiontoolbox import Image
img = Image.Read("monalisa.png")
img.draw_point((270, 194), "+", "eye", fontsize=1, color="yellow")

File ".../machinevisiontoolbox/base/graphics.py", line 782, in draw_point
    cv2.putText(
cv2.error: OpenCV(5.0.0) :-1: error: (-5:Bad argument) in function 'putText'
> Overload resolution failed:
>  - Layout of the output array img is incompatible with cv::Mat
>  - Expected Ptr<cv::UMat> for argument 'img'

Likely cause

The array that Image.Read returns is not C-contiguous. For monalisa.png it has shape (700, 677, 3), strides (677, 1, 473900) and flags["C_CONTIGUOUS"] == False: the memory is planar (channel-first) and the Image holds a transposed view. cv2.putText on 5.0 rejects an output array in that layout.

Not yet checked:

  • whether OpenCV 4 accepts it (the test machines used here all had OpenCV 5.0.0);
  • why Image.Read produces a planar layout;
  • whether the other draw_* functions in base/graphics.py that pass the image to cv2 drawing calls fail the same way.

Fix ideas

  • Make the draw_* functions work on a contiguous copy and write the result back (or return it), or
  • have Image.Read / Image construction keep arrays C-contiguous, which is the more general fix but touches more code.

Whichever is chosen, add a regression test that draws text onto an Image.Read image on OpenCV 5 (the existing suite passes on 4 and 5, so it does not exercise this path).

Found while investigating broken examples in the docs build; see the tech-debt issue #159.

Vorherrschende Sprache
Python
Sterne
224
Forks
31
Ø Merge
1 T. 22 Std.
Gemergte PRs (30 T.)
29

Entwicklungsumgebung

Erste Schritte

  1. Lesen Sie das ganze Issue und danach den Beitragsleitfaden des Projekts.
  2. Schreiben Sie ins Issue, dass Sie es übernehmen — das erspart doppelte Arbeit.
  3. Forken Sie das Repository und arbeiten Sie in einem Branch.
  4. Öffnen Sie einen Pull Request, der die Issue-Nummer nennt.

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