png.h

这个刚才那个的源代码

   png_byte filter_type;    /* must be PNG_FILTER_TYPE_BASE (from IHDR) */
   png_byte interlace_type; /* One of PNG_INTERLACE_NONE, PNG_INTERLACE_ADAM7 */

   /* The following is informational only on read, and not used on writes. */
   png_byte channels;       /* number of data channels per pixel (1, 2, 3, 4)*/
   png_byte pixel_depth;    /* number of bits per pixel */
   png_byte spare_byte;     /* to align the data, and for future use */
   png_byte signature[8];   /* magic bytes read by libpng from start of file */

   /* The rest of the data is optional.  If you are reading, check the
    * valid field to see if the information in these are valid.  If you
    * are writing, set the valid field to those chunks you want written,
    * and initialize the appropriate fields below.
    */

#if defined(PNG_gAMA_SUPPORTED) && defined(PNG_FLOATING_POINT_SUPPORTED)
   /* The gAMA chunk describes the gamma characteristics of the system
    * on which the image was created, normally in the range [1.0, 2.5].
    * Data is valid if (valid & PNG_INFO_gAMA) is non-zero.
    */
   float gamma; /* gamma value of image, if (valid & PNG_INFO_gAMA) */
#endif

#if defined(PNG_sRGB_SUPPORTED)
    /* GR-P, 0.96a */
    /* Data valid if (valid & PNG_INFO_sRGB) non-zero. */
   png_byte srgb_intent; /* sRGB rendering intent [0, 1, 2, or 3] */
#endif

#if defined(PNG_TEXT_SUPPORTED)
   /* The tEXt, and zTXt chunks contain human-readable textual data in
    * uncompressed, compressed, and optionally compressed forms, respectively.
    * The data in "text" is an array of pointers to uncompressed,
    * null-terminated C strings. Each chunk has a keyword that describes the
    * textual data contained in that chunk.  Keywords are not required to be
    * unique, and the text string may be empty.  Any number of text chunks may
    * be in an image.
    */
   int num_text; /* number of comments read/to write */
   int max_text; /* current size of text array */
   png_textp text; /* array of comments read/to write */
#endif /* PNG_TEXT_SUPPORTED */

#if defined(PNG_tIME_SUPPORTED)
   /* The tIME chunk holds the last time the displayed image data was
    * modified.  See the png_time struct for the contents of this struct.
    */
   png_time mod_time;
#endif

#if defined(PNG_sBIT_SUPPORTED)
   /* The sBIT chunk specifies the number of significant high-order bits
    * in the pixel data.  Values are in the range [1, bit_depth], and are
    * only specified for the channels in the pixel data.  The contents of
    * the low-order bits is not specified.  Data is valid if
    * (valid & PNG_INFO_sBIT) is non-zero.
    */
   png_color_8 sig_bit; /* significant bits in color channels */
#endif

#if defined(PNG_tRNS_SUPPORTED) || defined(PNG_READ_EXPAND_SUPPORTED) || \
defined(PNG_READ_BACKGROUND_SUPPORTED)
   /* The tRNS chunk supplies transparency data for paletted images and
    * other image types that don't need a full alpha channel.  There are
    * "num_trans" transparency values for a paletted image, stored in the
    * same order as the palette colors, starting from index 0.  Values
    * for the data are in the range [0, 255], ranging from fully transparent
    * to fully opaque, respectively.  For non-paletted images, there is a
    * single color specified that should be treated as fully transparent.
    * Data is valid if (valid & PNG_INFO_tRNS) is non-zero.
    */
   png_bytep trans; /* transparent values for paletted image */
   png_color_16 trans_values; /* transparent color for non-palette image */
#endif

#if defined(PNG_bKGD_SUPPORTED) || defined(PNG_READ_BACKGROUND_SUPPORTED)
   /* The bKGD chunk gives the suggested image background color if the
    * display program does not have its own background color and the image
    * is needs to composited onto a background before display.  The colors
    * in "background" are normally in the same color space/depth as the
    * pixel data.  Data is valid if (valid & PNG_INFO_bKGD) is non-zero.
    */
   png_color_16 background;
#endif

#if defined(PNG_oFFs_SUPPORTED)
   /* The oFFs chunk gives the offset in "offset_unit_type" units rightwards
    * and downwards from the top-left corner of the display, page, or other
    * application-specific co-ordinate space.  See the PNG_OFFSET_ defines
    * below for the unit types.  Valid if (valid & PNG_INFO_oFFs) non-zero.
    */
   png_int_32 x_offset; /* x offset on page */
   png_int_32 y_offset; /* y offset on page */
   png_byte offset_unit_type; /* offset units type */
#endif

#if defined(PNG_pHYs_SUPPORTED)
   /* The pHYs chunk gives the physical pixel density of the image for
    * display or printing in "phys_unit_type" units (see PNG_RESOLUTION_
    * defines below).  Data is valid if (valid & PNG_INFO_pHYs) is non-zero.
    */
   png_uint_32 x_pixels_per_unit; /* horizontal pixel density */
   png_uint_32 y_pixels_per_unit; /* vertical pixel density */
   png_byte phys_unit_type; /* resolution type (see PNG_RESOLUTION_ below) */
#endif

#if defined(PNG_hIST_SUPPORTED)
   /* The hIST chunk contains the relative frequency or importance of the
    * various palette entries, so that a viewer can intelligently select a
    * reduced-color palette, if required.  Data is an array of "num_palette"
    * values in the range [0,65535]. Data valid if (valid & PNG_INFO_hIST)
    * is non-zero.
    */
   png_uint_16p hist;
#endif

#ifdef PNG_cHRM_SUPPORTED
   /* The cHRM chunk describes the CIE color characteristics of the monitor
    * on which the PNG was created.  This data allows the viewer to do gamut
    * mapping of the input image to ensure that the viewer sees the same
    * colors in the image as the creator.  Values are in the range
    * [0.0, 0.8].  Data valid if (valid & PNG_INFO_cHRM) non-zero.
    */
#ifdef PNG_FLOATING_POINT_SUPPORTED
   float x_white;
   float y_white;
   float x_red;
   float y_red;
   float x_green;
   float y_green;
   float x_blue;
   float y_blue;
#endif
#endif

#if defined(PNG_pCAL_SUPPORTED)
   /* The pCAL chunk describes a transformation between the stored pixel
    * values and original physical data values used to create the image.
    * The integer range [0, 2^bit_depth - 1] maps to the floating-point
    * range given by [pcal_X0, pcal_X1], and are further transformed by a
    * (possibly non-linear) transformation function given by "pcal_type"
    * and "pcal_params" into "pcal_units".  Please see the PNG_EQUATION_
    * defines below, and the PNG-Group's PNG extensions document for a
    * complete description of the transformations and how they should be
    * implemented, and for a description of the ASCII parameter strings.
    * Data values are valid if (valid & PNG_INFO_pCAL) non-zero.
    */
   png_charp pcal_purpose;  /* pCAL chunk description string */
   png_int_32 pcal_X0;      /* minimum value */
   png_int_32 pcal_X1;      /* maximum value */
   png_charp pcal_units;    /* Latin-1 string giving physical units */
   png_charpp pcal_params;  /* ASCII strings containing parameter values */
   png_byte pcal_type;      /* equation type (see PNG_EQUATION_ below) */
   png_byte pcal_nparams;   /* number of parameters given in pcal_params */
#endif

/* New members added in libpng-1.0.6 */
#ifdef PNG_FREE_ME_SUPPORTED
   png_uint_32 free_me;     /* flags items libpng is responsible for freeing */
#endif

#if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
   /* storage for unknown chunks that the library doesn't recognize. */
   png_unknown_chunkp unknown_chunks;
   png_size_t unknown_chunks_num;
#endif

#if defined(PNG_iCCP_SUPPORTED)
   /* iCCP chunk data. */
   png_charp iccp_name;     /* profile name */
   png_charp iccp_profile;  /* International Color Consortium profile data */
                            /* Note to maintainer: should be png_bytep */
   png_uint_32 iccp_proflen;  /* ICC profile data length */
   png_byte iccp_compression; /* Always zero */
#endif

#if defined(PNG_sPLT_SUPPORTED)
   /* data on sPLT chunks (there may be more than one). */
   png_sPLT_tp splt_palettes;
   png_uint_32 splt_palettes_num;
#endif

#if defined(PNG_sCAL_SUPPORTED)
   /* The sCAL chunk describes the actual physical dimensions of the
    * subject matter of the graphic.  The chunk contains a unit specification
    * a byte value, and two ASCII strings representing floating-point
    * values.  The values are width and height corresponsing to one pixel
    * in the image.  This external representation is converted to double
    * here.  Data values are valid if (valid & PNG_INFO_sCAL) is non-zero.
    */
   png_byte scal_unit;         /* unit of physical scale */
#ifdef PNG_FLOATING_POINT_SUPPORTED
   double scal_pixel_width;    /* width of one pixel */
   double scal_pixel_height;   /* height of one pixel */
#endif
#ifdef PNG_FIXED_POINT_SUPPORTED
   png_charp scal_s_width;     /* string containing height */
   png_charp scal_s_height;    /* string containing width */
#endif
#endif

#if defined(PNG_INFO_IMAGE_SUPPORTED)
   /* Memory has been allocated if (valid & PNG_ALLOCATED_INFO_ROWS) non-zero */
   /* Data valid if (valid & PNG_INFO_IDAT) non-zero */
   png_bytepp row_pointers;        /* the image bits */
#endif

#if defined(PNG_FIXED_POINT_SUPPORTED) && defined(PNG_gAMA_SUPPORTED)
   png_fixed_point int_gamma; /* gamma of image, if (valid & PNG_INFO_gAMA) */
#endif

#if defined(PNG_cHRM_SUPPORTED) && defined(PNG_FIXED_POINT_SUPPORTED)
   png_fixed_point int_x_white;
   png_fixed_point int_y_white;
   png_fixed_point int_x_red;
   png_fixed_point int_y_red;
   png_fixed_point int_x_green;
   png_fixed_point int_y_green;
   png_fixed_point int_x_blue;
   png_fixed_point int_y_blue;
#endif

} png_info;

typedef png_info FAR * png_infop;
typedef png_info FAR * FAR * png_infopp;

/* Maximum positive integer used in PNG is (2^31)-1 */
#define PNG_MAX_UINT ((png_uint_32)0x7fffffffL)

/* These describe the color_type field in png_info. */
/* color type masks */
#define PNG_COLOR_MASK_PALETTE    1
#define PNG_COLOR_MASK_COLOR      2
#define PNG_COLOR_MASK_ALPHA      4

/* color types.  Note that not all combinations are legal */
#define PNG_COLOR_TYPE_GRAY 0
#define PNG_COLOR_TYPE_PALETTE  (PNG_COLOR_MASK_COLOR | PNG_COLOR_MASK_PALETTE)
#define PNG_COLOR_TYPE_RGB        (PNG_COLOR_MASK_COLOR)
#define PNG_COLOR_TYPE_RGB_ALPHA  (PNG_COLOR_MASK_COLOR | PNG_COLOR_MASK_ALPHA)
#define PNG_COLOR_TYPE_GRAY_ALPHA (PNG_COLOR_MASK_ALPHA)
/* aliases */
#define PNG_COLOR_TYPE_RGBA  PNG_COLOR_TYPE_RGB_ALPHA
#define PNG_COLOR_TYPE_GA  PNG_COLOR_TYPE_GRAY_ALPHA

/* This is for compression type. PNG 1.0-1.2 only define the single type. */
#define PNG_COMPRESSION_TYPE_BASE 0 /* Deflate method 8, 32K window */
#define PNG_COMPRESSION_TYPE_DEFAULT PNG_COMPRESSION_TYPE_BASE

/* This is for filter type. PNG 1.0-1.2 only define the single type. */
#define PNG_FILTER_TYPE_BASE      0 /* Single row per-byte filtering */
#define PNG_INTRAPIXEL_DIFFERENCING 64 /* Used only in MNG datastreams */
#define PNG_FILTER_TYPE_DEFAULT   PNG_FILTER_TYPE_BASE

/* These are for the interlacing type.  These values should NOT be changed. */
#define PNG_INTERLACE_NONE        0 /* Non-interlaced image */
#define PNG_INTERLACE_ADAM7       1 /* Adam7 interlacing */
#define PNG_INTERLACE_LAST        2 /* Not a valid value */

/* These are for the oFFs chunk.  These values should NOT be changed. */
#define PNG_OFFSET_PIXEL          0 /* Offset in pixels */
#define PNG_OFFSET_MICROMETER     1 /* Offset in micrometers (1/10^6 meter) */
#define PNG_OFFSET_LAST           2 /* Not a valid value */

/* These are for the pCAL chunk.  These values should NOT be changed. */
#define PNG_EQUATION_LINEAR       0 /* Linear transformation */
#define PNG_EQUATION_BASE_E       1 /* Exponential base e transform */
#define PNG_EQUATION_ARBITRARY    2 /* Arbitrary base exponential transform */
#define PNG_EQUATION_HYPERBOLIC   3 /* Hyperbolic sine transformation */
#define PNG_EQUATION_LAST         4 /* Not a valid value */

/* These are for the sCAL chunk.  These values should NOT be changed. */
#define PNG_SCALE_UNKNOWN         0 /* unknown unit (image scale) */
#define PNG_SCALE_METER           1 /* meters per pixel */
#define PNG_SCALE_RADIAN          2 /* radians per pixel */
#define PNG_SCALE_LAST            3 /* Not a valid value */

/* These are for the pHYs chunk.  These values should NOT be changed. */
#define PNG_RESOLUTION_UNKNOWN    0 /* pixels/unknown unit (aspect ratio) */
#define PNG_RESOLUTION_METER      1 /* pixels/meter */
#define PNG_RESOLUTION_LAST       2 /* Not a valid value */

/* These are for the sRGB chunk.  These values should NOT be changed. */
#define PNG_sRGB_INTENT_PERCEPTUAL 0
#define PNG_sRGB_INTENT_RELATIVE   1
#define PNG_sRGB_INTENT_SATURATION 2
#define PNG_sRGB_INTENT_ABSOLUTE   3
#define PNG_sRGB_INTENT_LAST       4 /* Not a valid value */

/* This is for text chunks */
#define PNG_KEYWORD_MAX_LENGTH     79

/* Maximum number of entries in PLTE/sPLT/tRNS arrays */
#define PNG_MAX_PALETTE_LENGTH	   256