API_COMPAT_CV2.md

Python compatibility helpers

TrainingSample 0.3.0 exposes a small set of OpenCV-style operations. Exported names and accepted integer codes are listed below.

The module is not a drop-in cv2 replacement. It does not export IMREAD_*, COLOR_*, VideoCapture, VideoWriter, or CascadeClassifier under those names.

Exported functions

Function	Signature
Decode	imdecode_py(buf, flags)
Color conversion	cvt_color_py(src, code)
Canny	canny_py(image, threshold1, threshold2)
Compatibility resize	resize_py(src, dsize, interpolation=None)
OpenCV bilinear resize	resize_bilinear_opencv(image, target_width, target_height)
OpenCV Lanczos resize	resize_lanczos4_opencv(image, target_width, target_height)
FourCC	fourcc_py(c1, c2, c3, c4)
OpenCV data path	get_opencv_data_path_py()

Decode

with open("image.jpg", "rb") as file:
    encoded = file.read()

rgb = tsr.imdecode_py(encoded, 1)
gray_rgb = tsr.imdecode_py(encoded, 0)
unchanged = tsr.imdecode_py(encoded, -1)

Flag	Meaning
-1	unchanged channel count where supported
0	grayscale replicated into (height, width, 3)
1	RGB

Decode uses the Rust image crate. Cargo explicitly enables JPEG, PNG, and WebP; the crate's default features are not disabled. Python bytes input is retained without cloning while the GIL is released; bytearray input is copied by PyO3 before decode.

Color conversion

gray = tsr.cvt_color_py(rgb, 7)
hsv = tsr.cvt_color_py(rgb, 41)

Code	Conversion
4	BGR to RGB
5	RGB to BGR
7	RGB to grayscale
8	grayscale to RGB
41	RGB to HSV
55	HSV to RGB

Resize

resized = tsr.resize_py(rgb, (224, 224), tsr.INTER_LINEAR)
batch = tsr.batch_resize_images([rgb], [(224, 224)])

Export	Value
INTER_NEAREST	0
INTER_LINEAR	1
INTER_CUBIC	2
INTER_LANCZOS4	4

batch_resize_images, resize_bilinear_opencv, and resize_lanczos4_opencv use OpenCV. resize_py uses the Rust compatibility implementation in cv_compat.

Canny

edges = tsr.canny_py(rgb, 50.0, 150.0)

canny_py uses imageproc and returns a three-dimensional uint8 NumPy array.

Video classes

Class	Constructor
PyVideoCapture	PyVideoCapture(filename)
PyVideoWriter	PyVideoWriter(filename, fourcc_str, fps, frame_size)

capture = tsr.PyVideoCapture("input.mp4")
opened = capture.is_opened()
ok, frame = capture.read()
capture.release()

fourcc = tsr.fourcc_py("M", "J", "P", "G")
writer = tsr.PyVideoWriter("output.avi", fourcc, 30.0, (640, 480))
if ok and frame is not None:
    writer.write(frame)
writer.release()

PyVideoCapture.from_bytes(source, suffix=".mp4") accepts bytes-like or file-like input and stores it in a temporary file for the lifetime of the capture object.

Supported PyVideoCapture.get property codes:

Code	Property
3	frame width
4	frame height
5	frames per second
7	frame count

Other property codes return 0.0.

Cascade class

classifier = tsr.PyCascadeClassifier("cascade.xml")
detections = classifier.detect_multi_scale(image)

Method	Signature
empty	empty()
detect_multi_scale	detect_multi_scale(image, scale_factor=None, min_neighbors=None)

Batch and specialized APIs

Function	Input requirement	Return
batch_crop_images	ndarray image	list of owned arrays
batch_center_crop_images	ndarray image	list of owned arrays
batch_random_crop_images	ndarray image	list of owned arrays
batch_resize_images	C-contiguous RGB	list of owned arrays
batch_resize_videos	contiguous RGB frames	list of owned arrays
batch_calculate_luminance	ndarray image	list of floats
batch_crop_images_zero_copy	C-contiguous	list of owned arrays
batch_center_crop_images_zero_copy	C-contiguous	list of owned arrays
batch_resize_images_zero_copy	C-contiguous RGB	array for single input; list for batch input
batch_resize_images_iterator	C-contiguous RGB	ResizeIterator

All crop boxes use (x, y, width, height). All target sizes use (width, height).

Exported class names

PyBatchProcessor
PyCascadeClassifier
PyTrueBatchProcessor
PyVideoCapture
PyVideoWriter
ResizeIterator