Za:  http://www.fileformat.info/format/gemraster/egff.htm

GEM raster files use a 16- or 18-byte header in the following format:

typedef struct _GemRaster
{
WORD   Version;         /* Image File Version (Always 1h) */
WORD   HeaderLength;    /* Size of Header in WORDs */
WORD   NumberOfPlanes;  /* Number of Planes */
WORD   PatternLength;   /* Pattern Definition Length */
WORD   PixelWidth;      /* Pixel Width in Micros */
WORD   PixelHeight;     /* Pixel Height in Micros */
WORD   ScanLineWidth;   /* Image Width in Pixels */
WORD   NumberOfLines    /* Image Height in Scan Lines */
WORD   BitImageFlag;    /* Multi-plane GrayColor Flag */
} GEMHEAD;

Version always has a value of one.

HeaderLength is either 8 or 9; if the value is 8, there is no BitImageFlag field in the header.

NumberOfPlanes contains the number of bits per pixel of the image source device (a scanner, for instance). This value is typically 1.

PatternLength contains a run-count value, which is usually 1. Any pattern code found in the encoded image data is repeated this number of times.

PixelHeight and PixelWidth are the pixel size in microns and are often 85 (55h), corresponding to 1/300 inch, or 300 dpi. The scale of the image may also be determined by using these pixel size values.

ScanLineWidth and NumberOfLines describe the size of the image in lines and pixels.

W TIGER masz:
0001 0008 0001 0002 00a9 0174 0180 0098 0480
Czyli rozmiar piksela w micros  jest ca 2 x mniejszy w poziomie (a9), niż w pionie (174, to jest "ca" 2*a9)

Pomocne, czy piszę oczywiste oczywistości?