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CoreGraphics.CGImageAlphaInfo Enumeration

Specifies the bitmap layout information.

Syntax

public enum CGImageAlphaInfo

Remarks

Quartz supports a number of color models: red, green and blue (RGB), cyan, magenta, yellow and key black (CMYK) and grayscale. Additionally, it is possible to specify an alpha channel that determines the transparency of the color when compositing an image with another one.

This enumeration determines the in-memory organization of the data and includes the color model, whether there is an alpha channel present and whether the component values have been premultiplied.

Pre-multiplication means that the values for red, green and blue have already been multiplied by the alpha value. This helps speed up rendering as it avoids three multiplications per pixel at render time.

Members

Member NameDescription
FirstAlpha channel comes first using 32-bits per pixel and 8 bits per channel (ARGB).
LastAlpha comes last, 32-bit per pixel, 8-bits per channel (RGBA).
NoneUsed for CMYK processing, 32-bits per pixel, 8-bits per channel (CMYK).
NoneSkipFirstThere is no alpha channel, 32-bits per pixel, 8 bits per channel, with the topmost channel ignored (xRGB).
NoneSkipLastThere is no alpha channel, 32-bits per pixel, 8 bits per channel, with the lower channel ignored (RGBx).
OnlyNo color data, only alpha channel data.
PremultipliedFirstPremultipled values for RGB, alpha channel comes first using 32-bits per pixel and 8 bits per channel (ARGB)
PremultipliedLastPremultipled values for RGB, alpha comes last, 32-bit per pixel, 8-bits per channel (RGBA).

Requirements

Namespace: CoreGraphics
Assembly: Xamarin.iOS (in Xamarin.iOS.dll)
Assembly Versions: 0.0.0.0

The members of CoreGraphics.CGImageAlphaInfo are listed below.

See Also: Enum

Public Fields

FirstCGImageAlphaInfo. Alpha channel comes first using 32-bits per pixel and 8 bits per channel (ARGB).
LastCGImageAlphaInfo. Alpha comes last, 32-bit per pixel, 8-bits per channel (RGBA).
NoneCGImageAlphaInfo. Used for CMYK processing, 32-bits per pixel, 8-bits per channel (CMYK).
NoneSkipFirstCGImageAlphaInfo. There is no alpha channel, 32-bits per pixel, 8 bits per channel, with the topmost channel ignored (xRGB).
NoneSkipLastCGImageAlphaInfo. There is no alpha channel, 32-bits per pixel, 8 bits per channel, with the lower channel ignored (RGBx).
OnlyCGImageAlphaInfo. No color data, only alpha channel data.
PremultipliedFirstCGImageAlphaInfo. Premultipled values for RGB, alpha channel comes first using 32-bits per pixel and 8 bits per channel (ARGB)
PremultipliedLastCGImageAlphaInfo. Premultipled values for RGB, alpha comes last, 32-bit per pixel, 8-bits per channel (RGBA).