How to load an external file

"Presumably this is just a byte-by-byte representation of the .BMP file's contents?"

Correct

"Before this could be used by the embedded device, the appropriate information would need to be extracted from the .BMP file and converted to a suitable form for the embedded device?"

I suppose that depends on the embedded application. For example, one application's BMP rendering implementation might be flexible and would use the parameters contained in the BITMAPINFO structure, while another application's implementation might be designed to only support a fixed format with parameters established by a priori agreement. The latter case would require preprocessing the BMP, but seems more reasonable for applications where an 8051 would be used.

The nifty thing about 010 Editor is that all you need to do is define a template (e.g., from the likes of file format descriptions on wotsit.org) describing the file's structure in a very C-like way and then you can write very C-like scripts to programmatically manipulate those files. The contents of SweetScape's BMP template below, which only defines how 010 Editor should display a file, might give you some idea how easy it would be to use built-in I/O functions (having similar C-like syntax) to perform custom file manipulation or data extraction.

Of course one could just write a little C program to do it too ;-)

//-----------------------------------
//--- 010 Editor v1.1 Binary Template
//
// File:    BMPTemplate.bt
// Author:  SweetScape Software
// Purpose: Defines a template for
//    parsing BMP files.
//-----------------------------------

// Define structures used in BMP files

typedef struct {   // bmfh
    CHAR    bfType[2];
    DWORD   bfSize;
    WORD    bfReserved1;
    WORD    bfReserved2;
    DWORD   bfOffBits;
} BITMAPFILEHEADER;

typedef struct {    // bmih
    DWORD   biSize;
    LONG    biWidth;
    LONG    biHeight;
    WORD    biPlanes;
    WORD    biBitCount;
    DWORD   biCompression;
    DWORD   biSizeImage;
    LONG    biXPelsPerMeter;
    LONG    biYPelsPerMeter;
    DWORD   biClrUsed;
    DWORD   biClrImportant;
} BITMAPINFOHEADER;

typedef struct {   // rgbq
    UBYTE   rgbBlue;
    UBYTE   rgbGreen;
    UBYTE   rgbRed;
    UBYTE   rgbReserved;
} RGBQUAD;

typedef struct {   // rgbt
    UBYTE   rgbBlue;
    UBYTE   rgbGreen;
    UBYTE   rgbRed;
} RGBTRIPLE;

//---------------------------------------------

// Define the headers
LittleEndian();
SetBackColor( cLtGray );
BITMAPFILEHEADER bmfh;
BITMAPINFOHEADER bmih;

// Check for header
if( bmfh.bfType != "BM" )
{
    Warning( "File is not a bitmap. Template stopped." );
    return -1;
}

// Define the color table
if( bmih.biBitCount != 24 )
{
    SetBackColor( cLtAqua );
    if( bmih.biClrUsed > 0 )
        RGBQUAD aColors[ bmih.biClrUsed ];
    else
        RGBQUAD aColors[ 1 << bmih.biBitCount ];
}

// Define the bytes of the data
SetBackColor( cNone );
if( bmih.biCompression > 0 )
{
    // Bytes are compressed
    if( bmih.biSizeImage > 0 )
        UBYTE rleData[ bmih.biSizeImage ];
    else
        UBYTE rleData[ bmfh.bfSize - FTell() ];
}
else
{
    // Calculate bytes per line and padding required
    local int bytesPerLine = (int)Ceil( bmih.biWidth * bmih.biBitCount / 8.0 );
    local int padding      = 4 - (bytesPerLine % 4);
    if( padding == 4 )
        padding = 0;

    // Define each line of the image
    struct BITMAPLINE {

        // Define color data
        if( bmih.biBitCount < 8 )
             UBYTE     imageData[ bytesPerLine ];
        else if( bmih.biBitCount == 8 )
             UBYTE     colorIndex[ bmih.biWidth ];
        else if( bmih.biBitCount == 24 )
             RGBTRIPLE colors[ bmih.biWidth ];

        // Pad if necessary
        if( padding != 0 )
             UBYTE padBytes[ padding ];

    } lines[ bmih.biHeight ];
}