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|
----------------
| FILE FORMATS |
----------------
PPM FORMAT
----------
To give you an idea of what a PPM file is, the following code will write
one out:
int **red, **green, **blue;
void WritePPM(char *fileName, int width, int height, int maxVal)
{
register int x, y;
unsigned char r, g, b;
fprintf(stdout, "P6\n");
fprintf(stdout, "%d %d\n", width, height);
fprintf(stdout, "%d\n", maxVal);
for ( y = 0; y < height; y++ )
for ( x = 0; x < width; x++ )
{
r = red[x][y]; g = green[x][y]; b = blue[x][y];
fwrite(&r, 1, 1, stdout);
fwrite(&g, 1, 1, stdout);
fwrite(&b, 1, 1, stdout);
}
}
maxVal is the maximum color value. It must be between 0 and 255 inclusive.
Generally speaking, it should be 255 always.
UCB YUV FORMAT
--------------
You should be aware that the YUV format used in the MPEG encoder is DIFFERENT
than the Abekas YUV format. The reason for this is that in MPEG, the U and
V components are subsampled 4:1.
To give you an idea of what format the YUV file must be in, the following
code will read in a YUV file:
unsigned char **y_data, **cr_data, **cb_data;
void ReadYUV(char *fileName, int width, int height)
{
FILE *fpointer;
register int y;
/* should allocate memory for y_data, cr_data, cb_data here */
fpointer = fopen(fileName, "r");
for (y = 0; y < height; y++) /* Y */
fread(y_data[y], 1, width, fpointer);
for (y = 0; y < height / 2; y++) /* U */
fread(cb_data[y], 1, width / 2, fpointer);
for (y = 0; y < height / 2; y++) /* V */
fread(cr_data[y], 1, width / 2, fpointer);
fclose(fpointer);
}
There are two reasons why you'd want to use YUV files rather than PPM files:
1) The YUV files are 50% the size of the corresponding PPM files
2) The ENCODER will run slightly faster, since it doesn't have to
do the RGB to YUV conversion itself.
ABEKAS YUV FORMAT
-----------------
The Abekas YUV Format interlaces the Y, U, and V values in a 4:2:2 format.
The interlacing pattern is
UYVY
for each group of 4 bytes in the file.
PHILLIPS YUV FORMAT
-------------------
The Phillips YUV Format interlaces the Y, U, and V values in a 4:2:2 format.
The interlacing pattern is
YVYU
for each group of 4 bytes in the file.
You may specify either ABEKAS, PHILLIPS, or UCB as the YUV_FORMAT when
encoding ; the encoder defaults to UCB YUV_FORMAT if not specified.
In addition, if you've got a weird interlacing format, you can also
try and de-interlace it by giving the YUV pattern in the YUV_FORMAT.
So a YUV 4:4:4 format would be
YUVYUV
|
