diff --git a/.gitignore b/.gitignore
index 26c6b31da..c43b51452 100644
--- a/.gitignore
+++ b/.gitignore
@@ -15,6 +15,9 @@ pids
 *.seed
 *.pid.lock
 
+# Python stuff
+.venv
+
 # Directory for instrumented libs generated by jscoverage/JSCover
 lib-cov
 
diff --git a/Development.md b/Development.md
new file mode 100644
index 000000000..ca55eee1a
--- /dev/null
+++ b/Development.md
@@ -0,0 +1,26 @@
+# Development documentation
+
+## Writing unit tests
+
+### Tests that compare with OpenCV
+
+[OpenCV](https://opencv.org/) is a popular image processing library for C++ and Python.
+We use it as a reference for some of the functions implemented in ImageJS.
+
+All images used for comparison with OpenCV are generated by the Python script [`test/img/opencv/generate.py`](./test/img/opencv/generate.py).
+
+To add a new test reference file:
+
+- Update [`generate.py`](./test/img/opencv/generate.py) with the OpenCV code that creates the file.
+- Run `generate.py` (see following paragraph).
+- Add the new filename to the [`TestImagePath`](./test/TestImagePath.ts) type (alphabetical order).
+
+To run the generation script, use the following steps:
+
+- Install Python 3.x
+- Run `python3 -m venv .venv` to create a virtual environment for the project
+- Activate the venv or run the local `pip` and `python` commands.
+  - `source .venv/bin/activate` (UNIX)
+  - `.venv/Scripts/Activate.ps1` (Windows)
+- Run `pip install opencv-python`
+- Run `python test/img/opencv/generate.py`
diff --git a/README.md b/README.md
index b96bf021a..da9dfa2d9 100644
--- a/README.md
+++ b/README.md
@@ -15,6 +15,10 @@ Image processing and manipulation in JavaScript.
 
 Look at the [examples](./examples) directory for how the API is being designed.
 
+## Development
+
+See [Development documentation](./Development.md).
+
 ## License
 
 [MIT](./LICENSE)
diff --git a/test/TestImagePath.ts b/test/TestImagePath.ts
index 92c92414a..9e513eef8 100644
--- a/test/TestImagePath.ts
+++ b/test/TestImagePath.ts
@@ -1,5 +1,39 @@
 // Update this type when test/img content changes.
 export type TestImagePath =
+  | 'align/cropped.png'
+  | 'align/cropped1.png'
+  | 'align/croppedRef.png'
+  | 'align/croppedRef1.png'
+  | 'correctColor/color-balance.png'
+  | 'correctColor/exposure-minus-1.png'
+  | 'correctColor/exposure-plus-1.png'
+  | 'correctColor/inverted.png'
+  | 'correctColor/offsets.png'
+  | 'correctColor/test.png'
+  | 'featureMatching/alphabet.jpg'
+  | 'featureMatching/alphabetRotated2.jpg'
+  | 'featureMatching/alphabetRotated5.jpg'
+  | 'featureMatching/alphabetRotated10.jpg'
+  | 'featureMatching/alphabetRotated-2.jpg'
+  | 'featureMatching/alphabetRotated-5.jpg'
+  | 'featureMatching/alphabetRotated-10.jpg'
+  | 'featureMatching/alphabetTranslated10.jpg'
+  | 'featureMatching/alphabetTranslated20.jpg'
+  | 'featureMatching/alphabetTranslated50.jpg'
+  | 'featureMatching/id-crops/crop1.png'
+  | 'featureMatching/id-crops/crop2.png'
+  | 'featureMatching/id-crops/crop3.png'
+  | 'featureMatching/patch.png'
+  | 'featureMatching/polygons/star.png'
+  | 'featureMatching/polygons/scaleneTriangle.png'
+  | 'featureMatching/polygons/scaleneTriangle2.png'
+  | 'featureMatching/polygons/scaleneTriangle10.png'
+  | 'featureMatching/polygons/scaleneTriangle90.png'
+  | 'featureMatching/polygons/scaleneTriangle180.png'
+  | 'featureMatching/polygons/polygon.png'
+  | 'featureMatching/polygons/polygon2.png'
+  | 'featureMatching/polygons/polygonRotated10degrees.png'
+  | 'featureMatching/polygons/polygonRotated180degrees.png'
   | 'formats/grey6.jpg'
   | 'formats/grey8.png'
   | 'formats/grey12.jpg'
@@ -15,74 +49,40 @@ export type TestImagePath =
   | 'formats/rgba32.png'
   | 'formats/rgba64.png'
   | 'formats/tif/grey8.tif'
+  | 'formats/tif/grey8-multi.tif'
   | 'formats/tif/grey16.tif'
+  | 'formats/tif/grey16-multi.tif'
   | 'formats/tif/grey32.tif'
   | 'formats/tif/greya16.tif'
   | 'formats/tif/greya32.tif'
+  | 'formats/tif/palette.tif'
   | 'formats/tif/rgb16.tif'
-  | 'formats/tif/rgba8.tif'
-  | 'formats/tif/grey8-multi.tif'
-  | 'formats/tif/grey16-multi.tif'
   | 'formats/tif/rgb16-multi.tif'
+  | 'formats/tif/rgba8.tif'
   | 'formats/tif/rgba8-multi.tif'
-  | 'formats/tif/palette.tif'
+  | 'morphology/alphabetCannyEdge.png'
+  | 'morphology/grayscaleCannyEdge.png'
+  | 'morphology/grayscaleClearBorder.png'
   | 'opencv/test.png'
   | 'opencv/testAffineTransform.png'
+  | 'opencv/testAntiClockwiseRot90.png'
   | 'opencv/testBlur.png'
+  | 'opencv/testClockwiseRot90.png'
   | 'opencv/testConvolution.png'
   | 'opencv/testGaussianBlur.png'
   | 'opencv/testInterpolate.png'
-  | 'opencv/testRotateBicubic.png'
-  | 'opencv/testRotateBilinear.png'
-  | 'opencv/testTranslate.png'
+  | 'opencv/testReflect.png'
   | 'opencv/testResizeBilinear.png'
   | 'opencv/testResizeNearest.png'
-  | 'opencv/testAntiClockwiseRot90.png'
-  | 'opencv/testClockwiseRot90.png'
+  | 'opencv/testRotateBicubic.png'
+  | 'opencv/testRotateBilinear.png'
   | 'opencv/testScale.png'
-  | 'opencv/testReflect.png'
-  | 'various/grayscale_by_zimmyrose.png'
-  | 'various/alphabet.jpg'
-  | 'various/without-metadata.jpg'
-  | 'morphology/alphabetCannyEdge.png'
-  | 'morphology/grayscaleCannyEdge.png'
-  | 'morphology/grayscaleClearBorder.png'
-  | 'correctColor/test.png'
-  | 'correctColor/color-balance.png'
-  | 'correctColor/exposure-minus-1.png'
-  | 'correctColor/exposure-plus-1.png'
-  | 'correctColor/inverted.png'
-  | 'correctColor/offsets.png'
-  | 'ssim/ssim-original.png'
-  | 'ssim/ssim-contrast.png'
-  | 'ssim/ssim-saltPepper.png'
+  | 'opencv/testTranslate.png'
   | 'ssim/ssim-blurry.png'
   | 'ssim/ssim-compressed.png'
-  | 'featureMatching/alphabet.jpg'
-  | 'featureMatching/alphabetRotated2.jpg'
-  | 'featureMatching/alphabetRotated5.jpg'
-  | 'featureMatching/alphabetRotated10.jpg'
-  | 'featureMatching/alphabetRotated-2.jpg'
-  | 'featureMatching/alphabetRotated-5.jpg'
-  | 'featureMatching/alphabetRotated-10.jpg'
-  | 'featureMatching/alphabetTranslated10.jpg'
-  | 'featureMatching/alphabetTranslated20.jpg'
-  | 'featureMatching/alphabetTranslated50.jpg'
-  | 'featureMatching/id-crops/crop1.png'
-  | 'featureMatching/id-crops/crop2.png'
-  | 'featureMatching/id-crops/crop3.png'
-  | 'featureMatching/patch.png'
-  | 'featureMatching/polygons/star.png'
-  | 'featureMatching/polygons/scaleneTriangle.png'
-  | 'featureMatching/polygons/scaleneTriangle2.png'
-  | 'featureMatching/polygons/scaleneTriangle10.png'
-  | 'featureMatching/polygons/scaleneTriangle90.png'
-  | 'featureMatching/polygons/scaleneTriangle180.png'
-  | 'featureMatching/polygons/polygon.png'
-  | 'featureMatching/polygons/polygon2.png'
-  | 'featureMatching/polygons/polygonRotated180degrees.png'
-  | 'featureMatching/polygons/polygonRotated10degrees.png'
-  | 'align/cropped.png'
-  | 'align/croppedRef.png'
-  | 'align/cropped1.png'
-  | 'align/croppedRef1.png';
+  | 'ssim/ssim-contrast.png'
+  | 'ssim/ssim-original.png'
+  | 'ssim/ssim-saltPepper.png'
+  | 'various/alphabet.jpg'
+  | 'various/grayscale_by_zimmyrose.png'
+  | 'various/without-metadata.jpg';
diff --git a/test/img/opencv/generate.py b/test/img/opencv/generate.py
index df354b696..d4a6f91dc 100644
--- a/test/img/opencv/generate.py
+++ b/test/img/opencv/generate.py
@@ -1,7 +1,13 @@
 import numpy as np
 import cv2 as cv
+from os import path
 
-img = cv.imread('./test.png')
+dirname = path.dirname(path.abspath(__file__))
+
+def writeImg(name, img):
+    cv.imwrite(path.join(dirname, name), img)
+
+img = cv.imread(path.join(dirname, 'test.png'))
 assert img is not None, "file could not be read, check with os.path.exists()"
 rows, cols = img.shape[0], img.shape[1]
 
@@ -10,67 +16,65 @@
 M = np.float32([[scale, 0, 0], [0, scale, 0]])
 dst = cv.warpAffine(img, M, dsize=(cols * scale, rows * scale), flags=cv.INTER_LINEAR, borderMode=cv.BORDER_CONSTANT,
                     borderValue=0)
-cv.imwrite('testScale.png', dst)
+writeImg('testScale.png', dst)
 
-# Image resizing by 10.
+# Image resizing.
 dst = cv.resize(img, (80, 100), interpolation=cv.INTER_NEAREST)
-cv.imwrite('testResizeNearest.png', dst)
+writeImg('testResizeNearest.png', dst)
 dst = cv.resize(img, (80, 100), interpolation=cv.INTER_LINEAR)
-cv.imwrite('testResizeBilinear.png', dst)
+writeImg('testResizeBilinear.png', dst)
 
 # Image rotate counter-clockwise by 90 degrees
 M = np.float32([[0, 1, 0], [-1, 0, cols - 1]])
 dst = cv.warpAffine(img, M, (rows, cols), flags=cv.INTER_LINEAR, borderMode=cv.BORDER_CONSTANT)
-cv.imwrite('testAntiClockwiseRot90.png', dst)
+writeImg('testAntiClockwiseRot90.png', dst)
 
 # Image rotate clockwise by 90 degrees
 M = np.float32([[0, -1, cols + 1], [1, 0, 0]])
 dst = cv.warpAffine(img, M, (rows, cols), flags=cv.INTER_LINEAR, borderMode=cv.BORDER_CONSTANT)
-cv.imwrite('testClockwiseRot90.png', dst)
+writeImg('testClockwiseRot90.png', dst)
 
 # Image interpolation
 matrix = cv.getRotationMatrix2D((2, 4), angle=30, scale=0.8)
 dst = cv.warpAffine(img, matrix, dsize=(cols, rows), flags=cv.INTER_NEAREST, borderMode=cv.BORDER_REFLECT)
-cv.imwrite('testInterpolate.png', dst)
+writeImg('testInterpolate.png', dst)
 
 # Image bilinear interpolation
 matrix = cv.getRotationMatrix2D((2, 4), angle=30, scale=1.4)
 dst = cv.warpAffine(img, matrix, dsize=(cols, rows), flags=cv.INTER_LINEAR, borderMode=cv.BORDER_REFLECT)
-cv.imwrite('testRotateBilinear.png', dst)
+writeImg('testRotateBilinear.png', dst)
 
 # Image bicubic interpolation
 matrix = cv.getRotationMatrix2D((2, 4), angle=30, scale=1.4)
 dst = cv.warpAffine(img, matrix, dsize=(cols, rows), flags=cv.INTER_CUBIC, borderMode=cv.BORDER_REFLECT)
-cv.imwrite('testRotateBicubic.png', dst)
+writeImg('testRotateBicubic.png', dst)
 
 # Image reflection
 M = np.float32([[1, 0, 0], [0, -1, rows - 1]])
 dst = cv.warpAffine(img, M, (cols, rows), flags=cv.INTER_LINEAR, borderMode=cv.BORDER_CONSTANT)
-cv.imwrite('testReflect.png', dst)
+writeImg('testReflect.png', dst)
 
 # Image translation
 M = np.float32([[1, 0, 2], [0, 1, 4]])
 dst = cv.warpAffine(img, M, (16, 20))
-cv.imwrite('testTranslate.png', dst)
+writeImg('testTranslate.png', dst)
 
 # Image affine transformation
 M = np.float32([[2, 1, 2], [-1, 1, 2]])
 dst = cv.warpAffine(img, M, (cols, rows), flags=cv.INTER_LINEAR, borderMode=cv.BORDER_CONSTANT)
-cv.imwrite('testAffineTransform.png', dst)
+writeImg('testAffineTransform.png', dst)
 
 # Image blur
 dst = cv.blur(img, (3, 5), borderType=cv.BORDER_REFLECT)
-cv.imwrite('testBlur.png', dst)
+writeImg('testBlur.png', dst)
 
 # Image gaussian blur
 kernel = cv.getGaussianKernel(3, 1)
 dst = cv.sepFilter2D(img, -1, kernel, kernel, borderType=cv.BORDER_REFLECT)
-cv.imwrite('testGaussianBlur.png', dst)
+writeImg('testGaussianBlur.png', dst)
 
 # Image convolution
 kernelX = np.float32([[0.1, 0.2, 0.3]])
-
 kernelY = np.float32([[0.4, 0.5, 0.6, -0.3, -0.4]])
-
 dst = cv.sepFilter2D(img, ddepth=-1, kernelX=kernelX, kernelY=kernelY, borderType=cv.BORDER_REFLECT)
-cv.imwrite('testConvolution.png', dst)
+writeImg('testConvolution.png', dst)