CGImageAlphaInfo CGImageAlphaInfo Enum

Definition

Specifies the bitmap layout information.

public enum CGImageAlphaInfo
type CGImageAlphaInfo = 
Inheritance
CGImageAlphaInfoCGImageAlphaInfo

Fields

First First 4

Alpha channel comes first using 32-bits per pixel and 8 bits per channel (ARGB).

Last Last 3

Alpha comes last, 32-bit per pixel, 8-bits per channel (RGBA).

None None 0

Used for CMYK processing, 32-bits per pixel, 8-bits per channel (CMYK).

NoneSkipFirst NoneSkipFirst 6

There is no alpha channel, 32-bits per pixel, 8 bits per channel, with the topmost channel ignored (xRGB).

NoneSkipLast NoneSkipLast 5

There is no alpha channel, 32-bits per pixel, 8 bits per channel, with the lower channel ignored (RGBx).

Only Only 7

No color data, only alpha channel data.

PremultipliedFirst PremultipliedFirst 2

Premultipled values for RGB, alpha channel comes first using 32-bits per pixel and 8 bits per channel (ARGB)

PremultipliedLast PremultipliedLast 1

Premultipled values for RGB, alpha comes last, 32-bit per pixel, 8-bits per channel (RGBA).

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.

Applies to