CGBitmapInfo 資料整理

 CGBitmapInfo 在自行產生圖檔資料時，需要設定此圖檔的相關資料，此時就要用下面參數來設定。

enum CGImageAlphaInfo {
    kCGImageAlphaNone,               /* For example, RGB. */
    kCGImageAlphaPremultipliedLast,  /* For example, premultiplied RGBA */
    kCGImageAlphaPremultipliedFirst, /* For example, premultiplied ARGB */
    kCGImageAlphaLast,               /* For example, non-premultiplied RGBA */
    kCGImageAlphaFirst,              /* For example, non-premultiplied ARGB */
    kCGImageAlphaNoneSkipLast,       /* For example, RBGX. */
    kCGImageAlphaNoneSkipFirst,      /* For example, XRGB. */
    kCGImageAlphaOnly                /* No color data, alpha data only */
};
typedef enum CGImageAlphaInfo CGImageAlphaInfo;

enum {
    kCGBitmapAlphaInfoMask = 0x1F,   //-> CGImageAlphaInfo
    kCGBitmapFloatComponents = (1 << 8),
  
    kCGBitmapByteOrderMask = 0x7000,
    kCGBitmapByteOrderDefault = (0 << 12),
    kCGBitmapByteOrder16Little = (1 << 12),
    kCGBitmapByteOrder32Little = (2 << 12),
    kCGBitmapByteOrder16Big = (3 << 12),
    kCGBitmapByteOrder32Big = (4 << 12)
};
typedef uint32_t CGBitmapInfo; /* Available in MAC OS X 10.4 & later. */

參考code

http://stackoverflow.com/questions/6073259/getting-rgb-pixel-data-from-cgimage

使用參考例 

CGBitmapContextCreate()的使用方法 

kCGBitmapAlphaInfoMask

The alpha information mask. Use this to extract alpha information that specifies whether a bitmap contains an alpha channel and how the alpha channel is generated.
Available in OS X v10.4 and later.
Declared in CGImage.h.

kCGBitmapFloatComponents

The components of a bitmap are floating-point values.
Available in OS X v10.4 and later.
Declared in CGImage.h.

kCGBitmapByteOrderMask

The byte ordering of pixel formats.
Available in OS X v10.4 and later.
Declared in CGImage.h.

kCGBitmapByteOrderDefault

The default byte order.
Available in OS X v10.4 and later.
Declared in CGImage.h.

kCGBitmapByteOrder16Little

16-bit, little endian format.
Available in OS X v10.4 and later.
Declared in CGImage.h.

kCGBitmapByteOrder32Little

32-bit, little endian format.
Available in OS X v10.4 and later.
Declared in CGImage.h.

kCGBitmapByteOrder16Big

16-bit, big endian format.
Available in OS X v10.4 and later.
Declared in CGImage.h.

kCGBitmapByteOrder32Big

32-bit, big endian format.
Available in OS X v10.4 and later.
Declared in CGImage.h.

kCGImageAlphaFirst

The alpha component is stored in the most significant bits of each pixel. For example, non-premultiplied ARGB.
Available in OS X v10.0 and later.
Declared in CGImage.h.

kCGImageAlphaLast

The alpha component is stored in the least significant bits of each pixel. For example, non-premultiplied RGBA.
Available in OS X v10.0 and later.
Declared in CGImage.h.

kCGImageAlphaNone

There is no alpha channel. If the total size of the pixel is greater than the space required for the number of color components in the color space, the least significant bits are ignored. This value is equivalent to kCGImageAlphaNoneSkipLast.
Available in OS X v10.0 and later.
Declared in CGImage.h.

kCGImageAlphaNoneSkipFirst

There is no alpha channel. If the total size of the pixel is greater than the space required for the number of color components in the color space, the most significant bits are ignored.
Available in OS X v10.0 and later.
Declared in CGImage.h.

kCGImageAlphaOnly

There is no color data, only an alpha channel.
Available in OS X v10.3 and later.
Declared in CGImage.h.

kCGImageAlphaNoneSkipLast

There is no alpha channel. If the total size of the pixel is greater than the space required for the number of color components in the color space, the least significant bits are ignored. This value is equivalent to kCGImageAlphaNone.
Available in OS X v10.0 and later.
Declared in CGImage.h.

kCGImageAlphaPremultipliedFirst

The alpha component is stored in the most significant bits of each pixel and the color components have already been multiplied by this alpha value. For example, premultiplied ARGB.
Available in OS X v10.0 and later.
Declared in CGImage.h.

kCGImageAlphaPremultipliedLast

The alpha component is stored in the least significant bits of each pixel and the color components have already been multiplied by this alpha value. For example, premultiplied RGBA.
Available in OS X v10.0 and later.
Declared in CGImage.h.