GrayCodePattern

Objective-C

@interface GrayCodePattern : StructuredLightPattern

Swift

class GrayCodePattern : StructuredLightPattern

Class implementing the Gray-code pattern, based on CITE: UNDERWORLD.

The generation of the pattern images is performed with Gray encoding using the traditional white and black colors.

The information about the two image axes x, y is encoded separately into two different pattern sequences. A projector P with resolution (P_res_x, P_res_y) will result in Ncols = log 2 (P_res_x) encoded pattern images representing the columns, and in Nrows = log 2 (P_res_y) encoded pattern images representing the rows. For example a projector with resolution 1024x768 will result in Ncols = 10 and Nrows = 10.

However, the generated pattern sequence consists of both regular color and color-inverted images: inverted pattern images are images with the same structure as the original but with inverted colors. This provides an effective method for easily determining the intensity value of each pixel when it is lit (highest value) and when it is not lit (lowest value). So for a a projector with resolution 1024x768, the number of pattern images will be Ncols * 2 + Nrows * 2 = 40.

Member of Structured_light

Methods

  • Constructor

    Declaration

    Objective-C

    + (nonnull GrayCodePattern *)create:(int)width height:(int)height;

    Swift

    class func create(width: Int32, height: Int32) -> GrayCodePattern

  • For a (x,y) pixel of a camera returns the corresponding projector pixel.

    The function decodes each pixel in the pattern images acquired by a camera into their corresponding decimal numbers representing the projector’s column and row, providing a mapping between camera’s and projector’s pixel.

    Declaration

    Objective-C

    - (BOOL)getProjPixel:(nonnull NSArray<Mat *> *)patternImages
                   x:(int)x
                   y:(int)y
             projPix:(nonnull Point2i *)projPix;

    Swift

    func getProjPixel(patternImages: [Mat], x: Int32, y: Int32, projPix: Point2i) -> Bool

    Parameters

    patternImages

    The pattern images acquired by the camera, stored in a grayscale vector < Mat >.
    x

    x coordinate of the image pixel.
    y

    y coordinate of the image pixel.
    projPix

    Projector’s pixel corresponding to the camera’s pixel: projPix.x and projPix.y are the image coordinates of the projector’s pixel corresponding to the pixel being decoded in a camera.

  • Get the number of pattern images needed for the graycode pattern.

    Declaration

    Objective-C

    - (size_t)getNumberOfPatternImages;

    Swift

    func getNumberOfPatternImages() -> Int

    Return Value

    The number of pattern images needed for the graycode pattern.

  • Generates the all-black and all-white images needed for shadowMasks computation.

    To identify shadow regions, the regions of two images where the pixels are not lit by projector’s light and thus where there is not coded information, the 3DUNDERWORLD algorithm computes a shadow mask for the two cameras views, starting from a white and a black images captured by each camera. This method generates these two additional images to project.

    Declaration

    Objective-C

    - (void)getImagesForShadowMasks:(nonnull Mat *)blackImage
                     whiteImage:(nonnull Mat *)whiteImage;

    Swift

    func getImagesForShadowMasks(blackImage: Mat, whiteImage: Mat)

    Parameters

    blackImage

    The generated all-black CV_8U image, at projector’s resolution.
    whiteImage

    The generated all-white CV_8U image, at projector’s resolution.

  • Sets the value for black threshold, needed for decoding (shadowsmasks computation).

    Black threshold is a number between 0-255 that represents the minimum brightness difference required for valid pixels, between the fully illuminated (white) and the not illuminated images (black); used in computeShadowMasks method.

    Declaration

    Objective-C

    - (void)setBlackThreshold:(size_t)value;

    Swift

    func setBlackThreshold(value: Int)

    Parameters

    value

    The desired black threshold value.

  • Sets the value for white threshold, needed for decoding.

    White threshold is a number between 0-255 that represents the minimum brightness difference required for valid pixels, between the graycode pattern and its inverse images; used in getProjPixel method.

    Declaration

    Objective-C

    - (void)setWhiteThreshold:(size_t)value;

    Swift

    func setWhiteThreshold(value: Int)

    Parameters

    value

    The desired white threshold value.