cvtColor

Image processingfunctionOpenCV 5.0.0

import { cvtColor } from '@banou/opencv-wasm'

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

Explore visually: Colour-space conversion →

Re-express pixels in a different channel order or colour representation.

VISUAL WALKTHROUGHColour

REFERENCE INPUTThree-channel colour samples

Colours depend on both channel order and the range assigned to each channel.

→

RESULTOne-channel luminance values

Weighted luminance converts three values into one. Other colour conversions preserve different properties.

Illustrative example. The stages explain the method; they are not a live OpenCV execution.

imgproc_misc

Converts an image from one color space to another.

The function converts an input image from one color space to another. In case of a transformation to-from RGB color space, the order of the channels should be specified explicitly (RGB or BGR). Note that the default color format in OpenCV is often referred to as RGB but it is actually BGR (the bytes are reversed). So the first byte in a standard (24-bit) color image will be an 8-bit Blue component, the second byte will be Green, and the third byte will be Red. The fourth, fifth, and sixth bytes would then be the second pixel (Blue, then Green, then Red), and so on.

The conventional ranges for R, G, and B channel values are:

• 0 to 255 for CV_8U images
• 0 to 65535 for CV_16U images
• 0 to 1 for CV_32F images

In case of linear transformations, the range does not matter. But in case of a non-linear transformation, an input RGB image should be normalized to the proper value range to get the correct results, for example, for RGB \rightarrow L*u*v* transformation. For example, if you have a 32-bit floating-point image directly converted from an 8-bit image without any scaling, then it will have the 0..255 value range instead of 0..1 assumed by the function. So, before calling #cvtColor , you need first to scale the image down:

    img *= 1./255;
    cvtColor(img, img, COLOR_BGR2Luv);

If you use #cvtColor with 8-bit images, the conversion will have some information lost. For many applications, this will not be noticeable but it is recommended to use 32-bit images in applications that need the full range of colors or that convert an image before an operation and then convert back.

If conversion adds the alpha channel, its value will set to the maximum of corresponding channel range: 255 for CV_8U, 65535 for CV_16U, 1 for CV_32F.

Note: The source image (src) must be of an appropriate type for the desired color conversion. see ColorConversionCodes See: imgproc_color_conversions

cvtColor(src: Mat, dst: Mat, code: number, dstCn: number, hint: number): void;

3 available overloads

cvtColor(src: Mat, dst: Mat, code: number): void;

cvtColor(src: Mat, dst: Mat, code: number, dstCn: number): void;

cvtColor(src: Mat, dst: Mat, code: number, dstCn: number, hint: number): void;

src

input image: 8-bit unsigned, 16-bit unsigned ( CV_16UC... ), or single-precision floating-point.

dst

Output destination, filled by the native operation. output image of the same size and depth as src.

code

color space conversion code (see #ColorConversionCodes).

dstCn

number of channels in the destination image; if the parameter is 0, the number of the channels is derived automatically from src and code.

hint

Implementation modification flags. See #AlgorithmHint

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.