TFW (World File) Format
Original Spanish by Ezequias Rodrigues da Rocha. English translation by Leonel Goncalves and Carl Anderson.
A World File has
1.000000000000000 0.000000000000000 0.000000000000000 -1.000000000000000 210326.500000000000000 4146551.500000000000000
Line 1: (A) X scale in resulting X direction Line 2: (B) Y scale in resulting X direction Line 3: (C) X scale in resulting Y direction Line 4: (D) Y scale in resulting Y direction Line 5: (E) X coordinate of the center of the center of rotation (the center of the Upper Left Pixel of the unrotated image) Line 6: (F) Y coordinate of the center of the center of rotation (the center of the Upper Left Pixel of the unrotated image)
or in algebraic form
X' = (A*X) + (B*Y) + E Y' = (C*X) + (D*Y) + F
where X' and Y' are georeferenced coordinates and x is pixel columns and y is pixels rows
D is negative because pixel rows increase opposite an increasing northing direction. B and C are zero for unrotated and unsheared georeferences A and D are zero for 90 and 270 degree rotations google world file ax + by center for more references
Anexo I: Formato TFW. Un ejemplo de fichero TFW serÃa el siguiente:
1.000000000000000 0.000000000000000 0.000000000000000 -1.000000000000000 210326.500000000000000 4146551.500000000000000
La primera lÃnea indica el tamaño del pixel en la dirección X, en metros, de la imágen. La segunda linea nos indica la coordenada pixel X, de un punto cualquiera de la imágen (lo normal la esquina superior izquierda (xmin, ymax). La tercera lÃnea la coordenada pixel Y del punto de la imágen. La cuarta lÃnea el tamaño del pixel en la dirección Y, en metros de la imágen. Un valor negativo indica que el punto de coordenada Ypixel = 0 es el punto que tiene un valor de coordenada Y real mayor. La quinta linea nos da la coordenada X real del punto utilizado para georreferenciar la imágen. La sexta lÃnea la coordenada Y real del citado punto.
Ole Rahn adds:
Just one thing: As far as I know (I was corrected by a user myself) the world file extension consists of the following parts:
[dot] [1st letter of the image's extension] [last letter of the image's extension] [w]
... so for a PNG it should be: ".pgw" (not ".pngw")
A good explanation in english can also be found at: http://www.feflow.info/html/help/general/file_format.html#tfw_file