bmp.htm

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    layout of a device-independent bitmap (dib) file.<br>
    <br>
    member description<br>
    <br>
    bftype specifies the type of file. this member must be bm. <br>
    bfsize specifies the size of the file, in bytes. <br>
    bfreserved1 reserved; must be set to zero. <br>
    bfreserved2 reserved; must be set to zero.<br>
    bfoffbits specifies the byte offset from the bitmapfileheader structure<br>
    to the actual bitmap data in the file.<br>
    <br>
    comments<br>
    <br>
    a bitmapinfo or bitmapcoreinfo structure immediately follows the<br>
    bitmapfileheader structure in the dib file.<br>
    <br>
    see also<br>
    <br>
    bitmapcoreinfo, bitmapinfo <br>
    <br>
    <br>
    ==============================================================================<br>
    bitmapinfo (3.0)<br>
    <br>
    <br>
    <br>
    typedef struct tagbitmapinfo { /* bmi */<br>
    bitmapinfoheader bmiheader;<br>
    rgbquad bmicolors[1];<br>
    } bitmapinfo;<br>
    <br>
    the bitmapinfo structure fully defines the dimensions and color information<br>
    for a windows 3.0 or later device-independent bitmap (dib).<br>
    <br>
    member description<br>
    <br>
    bmiheader specifies a bitmapinfoheader structure that contains<br>
    information about the dimensions and color format of a dib.<br>
    <br>
    bmicolors specifies an array of rgbquad structures that define the<br>
    colors in the bitmap.<br>
    <br>
    comments<br>
    <br>
    a windows 3.0 or later dib consists of two distinct parts: a bitmapinfo<br>
    structure, which describes the dimensions and colors of the bitmap, and an<br>
    array of bytes defining the pixels of the bitmap. the bits in the array are<br>
    packed together, but each scan line must be zero-padded to end on a long<br>
    boundary. segment boundaries, however, can appear anywhere in the bitmap. the<br>
    origin of the bitmap is the lower-left corner.<br>
    <br>
    the bibitcount member of the bitmapinfoheader structure determines the number<br>
    of bits which define each pixel and the maximum number of colors in the<br>
    bitmap. this member may be set to any of the following values:<br>
    <br>
    value meaning<br>
    <br>
    1 the bitmap is monochrome, and the bmcicolors member must contain two<br>
    entries. each bit in the bitmap array represents a pixel. if the bit is<br>
    clear, the pixel is displayed with the color of the first entry in the<br>
    bmcicolors table. if the bit is set, the pixel has the color of the second<br>
    entry in the table.<br>
    <br>
    4 the bitmap has a maximum of 16 colors, and the bmcicolors member<br>
    contains 16 entries. each pixel in the bitmap is represented by a four-bit<br>
    index into the color table.<br>
    <br>
    for example, if the first byte in the bitmap is 0x1f, the byte represents two<br>
    pixels. the first pixel contains the color in the second table entry, and the<br>
    second pixel contains the color in the sixteenth table entry.<br>
    <br>
    8 the bitmap has a maximum of 256 colors, and the bmcicolors member<br>
    contains 256 entries. in this case, each byte in the array represents a<br>
    single pixel.<br>
    <br>
    24 the bitmap has a maximum of 2^24 colors. the bmcicolors member is<br>
    null, and each 3-byte sequence in the bitmap array represents the relative<br>
    intensities of red, green, and blue, respectively, of a pixel.<br>
    <br>
    the biclrused member of the bitmapinfoheader structure specifies the number<br>
    of color indexes in the color table actually used by the bitmap. if the<br>
    biclrused member is set to zero, the bitmap uses the maximum number of colors<br>
    corresponding to the value of the bibitcount member.<br>
    <br>
    the colors in the bmicolors table should appear in order of importance.<br>
    alternatively, for functions that use dibs, the bmicolors member can be an<br>
    array of 16-bit unsigned integers that specify an index into the currently<br>
    realized logical palette instead of explicit rgb values. in this case, an<br>
    application using the bitmap must call dib functions with the wusage<br>
    parameter set to dib_pal_colors.<br>
    <br>
    note: the bmicolors member should not contain palette indexes if the bitmap<br>
    is to be stored in a file or transferred to another application. unless the<br>
    application uses the bitmap exclusively and under its complete control, the<br>
    bitmap color table should contain explicit rgb values.<br>
    <br>
    see also<br>
    <br>
    bitmapinfoheader, rgbquad <br>
    <br>
    ==============================================================================<br>
    bitmapinfoheader (3.0)<br>
    <br>
    <br>
    <br>
    typedef struct tagbitmapinfoheader { /* bmih */<br>
    dword bisize;<br>
    long biwidth;<br>
    long biheight;<br>
    word biplanes;<br>
    word bibitcount;<br>
    dword bicompression;<br>
    dword bisizeimage;<br>
    long bixpelspermeter;<br>
    long biypelspermeter;<br>
    dword biclrused;<br>
    dword biclrimportant;<br>
    } bitmapinfoheader;<br>
    <br>
    the bitmapinfoheader structure contains information about the dimensions and<br>
    color format of a windows 3.0 or later device-independent bitmap (dib).<br>
    <br>
    member description<br>
    <br>
    bisize specifies the number of bytes required by the<br>
    bitmapinfoheader structure.<br>
    <br>
    biwidth specifies the width of the bitmap, in pixels. <br>
    biheightspecifies the height of the bitmap, in pixels. <br>
    <br>
    biplanesspecifies the number of planes for the target device. this<br>
    member must be set to 1.<br>
    <br>
    bibitcount specifies the number of bits per pixel. this value must be 1,<br>
    4, 8, or 24.<br>
    <br>
    bicompression specifies the type of compression for a compressed bitmap. it<br>
    can be one of the following values:<br>
    <br>
    value meaning<br>
    <br>
    bi_rgb specifies that the bitmap is not compressed. <br>
    <br>
    bi_rle8 specifies a run-length encoded format for bitmaps with 8 bits<br>
    per pixel. the compression format is a 2-byte format consisting of a count<br>
    byte followed by a byte containing a color index. for more information, see<br>
    the following comments section.<br>
    <br>
    bi_rle4 specifies a run-length encoded format for bitmaps with 4 bits<br>
    per pixel. the compression format is a 2-byte format consisting of a count<br>
    byte followed by two word-length color indexes. for more information, see<br>
    the following comments section.<br>
    <br>
    bisizeimage specifies the size, in bytes, of the image. it is valid to<br>
    set this member to zero if the bitmap is in the bi_rgb format.<br>
    <br>
    bixpelspermeter specifies the horizontal resolution, in pixels per meter, of<br>
    the target device for the bitmap. an application can use this value to select<br>
    a bitmap from a resource group that best matches the characteristics of the<br>
    current device.<br>
    <br>
    biypelspermeter specifies the vertical resolution, in pixels per meter, of<br>
    the target device for the bitmap.<br>
    <br>
    biclrused specifies the number of color indexes in the color table<br>
    actually used by the bitmap. if this value is zero, the bitmap uses the<br>
    maximum number of colors corresponding to the value of the bibitcount member.<br>
    for more information on the maximum sizes of the color table, see the<br>
    description of the bitmapinfo structure earlier in this topic.<br>
    <br>
    if the biclrused member is nonzero, it specifies the actual number of colors<br>
    that the graphics engine or device driver will access if the bibitcount<br>
    member is less than 24. if bibitcount is set to 24, biclrused specifies the<br>
    size of the reference color table used to optimize performance of windows<br>
    color palettes. if the bitmap is a packed bitmap (that is, a bitmap in which<br>
    the bitmap array immediately follows the bitmapinfo header and which is<br>
    referenced by a single pointer), the biclrused member must be set to zero or<br>
    to the actual size of the color table.<br>
    <br>
    biclrimportant specifies the number of color indexes that are considered<br>
    important for displaying the bitmap. if this value is zero, all colors are<br>
    important.<br>
    <br>
    comments<br>
    <br>
    the bitmapinfo structure combines the bitmapinfoheader structure and a color<br>
    table to provide a complete definition of the dimensions and colors of a<br>
    windows 3.0 or later dib. for more information about specifying a windows 3.0<br>
    dib, see the description of the bitmapinfo structure.<br>
    <br>
    an application should use the information stored in the bisize member to<br>
    locate the color table in a bitmapinfo structure as follows:<br>
    <br>
    pcolor = ((lpstr) pbitmapinfo + (word) (pbitmapinfo-&gt;bmiheader.bisize))<br>
    <br>
    windows supports formats for compressing bitmaps that define their colors<br>
    with 8 bits per pixel and with 4 bits per pixel. compression reduces the disk<br>
    and memory storage required for the bitmap. the following paragraphs describe<br>
    these formats.<br>
    <br>
    bi_rle8<br>
    <br>
    when the bicompression member is set to bi_rle8, the bitmap is compressed<br>
    using a run-length encoding format for an 8-bit bitmap. this format may be<br>
    compressed in either of two modes: encoded and absolute. both modes can occur<br>
    anywhere throughout a single bitmap.<br>
    <br>
    encoded mode consists of two bytes: the first byte specifies the number of<br>
    consecutive pixels to be drawn using the color index contained in the second<br>
    byte. in addition, the first byte of the pair can be set to zero to indicate<br>
    an escape that denotes an end of line, end of bitmap, or a delta. the<br>
    interpretation of the escape depends on the value of the second byte of the<br>
    pair. the following list shows the meaning of the second byte:<br>
    <br>
    value meaning<br>
    <br>
    0 end of line. <br>
    1 end of bitmap. <br>
    2 delta. the two bytes following the escape contain unsigned values<br>
    indicating the horizontal and vertical offset of the next pixel from the<br>
    current position.<br>
    <br>
    absolute mode is signaled by the first byte set to zero and the second byte<br>
    set to a value between 0x03 and 0xff. in absolute mode, the second byte<br>
    represents the number of bytes that follow, each of which contains the color<br>
    index of a single pixel. when the second byte is set to 2 or less, the escape<br>
    has the same meaning as in encoded mode. in absolute mode, each run must be<br>
    aligned on a word boundary. the following example shows the hexadecimal<br>
    values of an 8-bit compressed bitmap:<br>
    <br>
    <br>
    <br>
    03 04 05 06 00 03 45 56 67 00 02 78 00 02 05 01<br>
    02 78 00 00 09 1e 00 01<br>
    <br>
    this bitmap would expand as follows (two-digit values represent a color index<br>
    for a single pixel):<br>
    <br>
    <br>
    <br>
    04 04 04<br>
    06 06 06 06 06<br>
    45 56 67<br>
    78 78<br>
    move current position 5 right and 1 down<br>
    78 78<br>
    end of line<br>
    1e 1e 1e 1e 1e 1e 1e 1e 1e<br>
    end of rle bitmap<br>
    <br>
    bi_rle4<br>
    <br>
    when the bicompression member is set to bi_rle4, the bitmap is compressed<br>
    using a run-length encoding (rle) format for a 4-bit bitmap, which also uses<br>
    encoded and absolute modes. in encoded mode, the first byte of the pair<br>
    contains the number of pixels to be drawn using the color indexes in the<br>
    second byte. the second byte contains two color indexes, one in its<br>
    high-order nibble (that is, its low-order four bits) and one in its low-order<br>
    nibble. the first of the pixels is drawn using the color specified by the<br>
    high-order nibble, the second is drawn using the color in the low-order<br>
    nibble, the third is drawn with the color in the high-order nibble, and so<br>
    on, until all the pixels specified by the first byte have been drawn. in<br>
    absolute mode, the first byte contains zero, the second byte contains the<br>
    number of color indexes that follow, and subsequent bytes contain color<br>