class

CrImage::YCbCr

Inherits CrImage::Image / Reference / Object

YCbCr is an in-memory image using the Y'CbCr color space.

Y'CbCr separates luminance (Y') from chrominance (Cb, Cr), commonly used in JPEG compression and video encoding. There is one Y sample per pixel, but Cb and Cr samples can span multiple pixels depending on the subsampling ratio.

Memory layout:

y_stride : Y slice index delta between vertically adjacent pixels
c_stride : Cb/Cr slice index delta between vertically adjacent chroma samples

Typical stride relationships (y_stride and y.size are multiples of 8):

For 4:4:4: c_stride == y_stride//1 && cb.size == cr.size == y.size//1
For 4:2:2: c_stride == y_stride//2 && cb.size == cr.size == y.size//2
For 4:2:0: c_stride == y_stride//2 && cb.size == cr.size == y.size//4
For 4:4:0: c_stride == y_stride//1 && cb.size == cr.size == y.size//2
For 4:1:1: c_stride == y_stride//4 && cb.size == cr.size == y.size//4
For 4:1:0: c_stride == y_stride//4 && cb.size == cr.size == y.size//8

Example:

# Create YCbCr image with 4:2:0 subsampling (JPEG standard)
img = CrImage::YCbCr.new(
  CrImage.rect(0, 0, 640, 480),
  CrImage::YCbCrSubSampleRatio::YCbCrSubsampleRatio420
)

# Set pixel in YCbCr space
img.set_ycbcr(100, 100, CrImage::Color::YCbCr.new(128, 128, 128))

Constructors

new(rect : Rectangle, sub_sample_ratio : YCbCrSubSampleRatio)

Source

new(y : Slice(UInt8) = Bytes.empty, cb : Slice(UInt8) = Bytes.empty, cr : Slice(UInt8) = Bytes.empty, y_stride : Int32 = 0, c_stride : Int32 = 0, sub_sample_ratio : CrImage::YCbCrSubSampleRatio = YCbCrSubSampleRatio::YCbCrSubsampleRatio444, rect : CrImage::Rectangle = Rectangle.zero)

Source

Instance methods

at(x : Int32, y : Int32) : Color::Color

Returns the color of the pixel at (x,y).

If coordinates are outside bounds, returns a default color (typically transparent black) rather than raising an exception. This simplifies image processing algorithms.

at(bounds().min.x, bounds().min.y) returns the upper-left pixel of the grid.
at(bounds().max.x-1, bounds().max.y-1) returns the lower-right one.

For explicit nil on out-of-bounds, concrete types provide at? method.

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bounds

bounds returns the domain for which at can return non-zero color. The bounds do not necessarily contain the point(0,0).

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c_offset(x, y)

returns the index of the first element of cb or cr that corresponds to the pixel at (x,y)

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c_stride

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c_stride=(c_stride : Int32)

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cb=(cb : Bytes)

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color_model

color_model returns the Image's color model

cr=(cr : Bytes)

opaque?

rect

rect=(rect : Rectangle)

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set(x : Int32, y : Int32, c : Color::Color)

Sets the color of the pixel at (x,y).

If the provided coordinates are not within bounds, this method does nothing (no-op). This simplifies drawing operations that may extend beyond image boundaries.

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set_ycbcr(x : Int32, y : Int32, c : Color::YCbCr)

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sub_image(r : Rectangle) : Image

sub_image returns an image representing the portion of the image visible though r. the returned value shares pixes with the original image.

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sub_sample_ratio

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sub_sample_ratio=(sub_sample_ratio : YCbCrSubSampleRatio)

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y=(y : Bytes)

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