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opencv-wasm

imwrite

Image codecsfunctionOpenCV 5.0.0
import { imwrite } from '@banou/opencv-wasm'

Use after await initOpenCV(). See the initialization and named imports guide.

ARGUMENTSfilename, img, params
FUNCTIONimwrite
RETURN TYPEboolean
Call structure. A void return can still write to destination arguments. The parameter descriptions define inputs, outputs and ownership.

Saves an image to a specified file.

The function imwrite saves the image to the specified file. The image format is chosen based on the filename extension (see cv::imread for the list of extensions). In general, only 8-bit unsigned (CV_8U) single-channel or 3-channel (with 'BGR' channel order) images can be saved using this function, with these exceptions:

  • With BMP encoder, 8-bit unsigned (CV_8U) images can be saved.
    • BMP images with an alpha channel can be saved using this function. To achieve this, create an 8-bit 4-channel (CV_8UC4) BGRA image, ensuring the alpha channel is the last component. Fully transparent pixels should have an alpha value of 0, while fully opaque pixels should have an alpha value of 255. OpenCV v4.13.0 or later use BI_BITFIELDS compression as default. See IMWRITE_BMP_COMPRESSION.
  • With OpenEXR encoder, only 32-bit float (CV_32F) images can be saved. More than 4 channels can be saved. (imread can load it then.)
    • 8-bit unsigned (CV_8U) images are not supported.
  • With Radiance HDR encoder, non 64-bit float (CV_64F) images can be saved.
    • All images will be converted to 32-bit float (CV_32F).
  • With JPEG 2000 encoder, 8-bit unsigned (CV_8U) and 16-bit unsigned (CV_16U) images can be saved.
  • With JPEG XL encoder, 8-bit unsigned (CV_8U), 16-bit unsigned (CV_16U) and 32-bit float(CV_32F) images can be saved.
    • JPEG XL images with an alpha channel can be saved using this function. To achieve this, create an 8-bit 4-channel (CV_8UC4) / 16-bit 4-channel (CV_16UC4) / 32-bit float 4-channel (CV_32FC4) BGRA image, ensuring the alpha channel is the last component. Fully transparent pixels should have an alpha value of 0, while fully opaque pixels should have an alpha value of 255/65535/1.0.
  • With PAM encoder, 8-bit unsigned (CV_8U) and 16-bit unsigned (CV_16U) images can be saved.
  • With PNG encoder, 8-bit unsigned (CV_8U) and 16-bit unsigned (CV_16U) images can be saved.
    • PNG images with an alpha channel can be saved using this function. To achieve this, create an 8-bit 4-channel (CV_8UC4) / 16-bit 4-channel (CV_16UC4) BGRA image, ensuring the alpha channel is the last component. Fully transparent pixels should have an alpha value of 0, while fully opaque pixels should have an alpha value of 255/65535(see the code sample below).
  • With PGM/PPM encoder, 8-bit unsigned (CV_8U) and 16-bit unsigned (CV_16U) images can be saved.
  • With TIFF encoder, 8-bit unsigned (CV_8U), 8-bit signed (CV_8S), 16-bit unsigned (CV_16U), 16-bit signed (CV_16S), 32-bit unsigned (CV_32U), 32-bit signed (CV_32S), 64-bit unsigned (CV_64U), 64-bit signed (CV_64S), 32-bit float (CV_32F) and 64-bit float (CV_64F) images can be saved.
    • Multiple images (vector of Mat) can be saved in TIFF format (see the code sample below).
    • 32-bit float 3-channel (CV_32FC3) TIFF images can be saved using the LogLuv high dynamic range encoding (4 bytes per pixel) through TIFF_COMPRESSION_SGILOG or (3 bytes per pixel) through TIFF_COMPRESSION_SGILOG24.
    • Other compression schemes (LZW...) are supported as well for 32F depth, but the efficiency might not be very good for the floating-point representation bit patterns.
  • With GIF encoder, 8-bit unsigned (CV_8U) images can be saved.
    • GIF images with an alpha channel can be saved using this function. To achieve this, create an 8-bit 4-channel (CV_8UC4) BGRA image, ensuring the alpha channel is the last component. Fully transparent pixels should have an alpha value of 0, while fully opaque pixels should have an alpha value of 255.
    • 8-bit single-channel images (CV_8UC1) are not supported due to GIF's limitation to indexed color formats.
  • With AVIF encoder, 8-bit unsigned (CV_8U) and 16-bit unsigned (CV_16U) images can be saved.
    • CV_16U images can be saved as only 10-bit or 12-bit (not 16-bit). See IMWRITE_AVIF_DEPTH.
    • AVIF images with an alpha channel can be saved using this function. To achieve this, create an 8-bit 4-channel (CV_8UC4) / 16-bit 4-channel (CV_16UC4) BGRA image, ensuring the alpha channel is the last component. Fully transparent pixels should have an alpha value of 0, while fully opaque pixels should have an alpha value of 255 (8-bit) / 1023 (10-bit) / 4095 (12-bit) (see the code sample below).

If the image format is not supported, the image will be converted to 8-bit unsigned (CV_8U) and saved that way.

If the format, depth or channel order is different, use Mat::convertTo and cv::cvtColor to convert it before saving. Or, use the universal FileStorage I/O functions to save the image to XML or YAML format.

The sample below shows how to create a BGRA image, how to set custom compression parameters and save it to a PNG file. It also demonstrates how to save multiple images in a TIFF file:

imwrite(filename: EmbindString, img: Mat, params: IntVector): boolean;
2 available overloads
imwrite(filename: EmbindString, img: Mat): boolean;
imwrite(filename: EmbindString, img: Mat, params: IntVector): boolean;
filename

Name of the file.

img

(Mat or vector of Mat) Image or Images to be saved.

params

Format-specific parameters encoded as pairs (paramId_1, paramValue_1, paramId_2, paramValue_2, ... .) see cv::ImwriteFlags

Returns

true if the image is successfully written to the specified file; false otherwise.

Upstream declaration ↗

These signatures describe this package. Upstream documentation can mention optional backends that are absent from this build. Check runtime compatibility before choosing a backend or file format.