The format of the string data used in the imageop module is described
as "This is the same format as used by gl.lrectwrite() and the imgfile module." This implies a certain byte order in multi-byte pixel formats. However, the code was originally written on an SGI (big-endian) and *uses* the fact that bytes are stored in a particular order in ints. This means that the code uses and produces different byte order on little-endian systems. This fix adds a module-level flag "backward_compatible" (default not set, and if not set, behaves as if set to 1--i.e. backward compatible) that can be used on a little-endian system to use the same byte order as the SGI. Using this flag it is then possible to prepare SGI-compatible images on a little-endian system. This patch is the result of a (small) discussion on python-dev and was submitted to SourceForge as patch #874358.
This commit is contained in:
Sjoerd Mullender
parent
2e5e6445e7
commit
7e6bbe1516
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@ -86,3 +86,15 @@ Convert a 4-bit greyscale image to an 8-bit greyscale image.
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\begin{funcdesc}{grey22grey}{image, width, height}
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Convert a 2-bit greyscale image to an 8-bit greyscale image.
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\end{funcdesc}
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\begin{datadesc}{backward_compatible}
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If set to 0, the functions in this module use a non-backward
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compatible way of representing multi-byte pixels on little-endian
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systems. The SGI for which this module was originally written is a
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big-endian system, so setting this variable will have no effect.
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However, the code wasn't originally intended to run on anything else,
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so it made assumptions about byte order which are not universal.
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Setting this variable to 0 will cause the byte order to be reversed on
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little-endian systems, so that it then is the same as on big-endian
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systems.
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\end{datadesc}
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@ -24,7 +24,54 @@ typedef unsigned long Py_UInt32;
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#define LONGP(cp, xmax, x, y) ((Py_Int32 *)(cp+4*(y*xmax+x)))
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static PyObject *ImageopError;
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static PyObject *ImageopDict;
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/* If this function returns true (the default if anything goes wrong), we're
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behaving in a backward-compatible way with respect to how multi-byte pixels
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are stored in the strings. The code in this module was originally written
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for an SGI which is a big-endian system, and so the old code assumed that
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4-byte integers hold the R, G, and B values in a particular order.
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However, on little-endian systems the order is reversed, and so not
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actually compatible with what gl.lrectwrite and imgfile expect.
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(gl.lrectwrite and imgfile are also SGI-specific, however, it is
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conceivable that the data handled here comes from or goes to an SGI or that
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it is otherwise used in the expectation that the byte order in the strings
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is as specified.)
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The function returns the value of the module variable
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"backward_compatible", or 1 if the variable does not exist or is not an
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int.
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*/
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static int
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imageop_backward_compatible(void)
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{
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static PyObject *bcos;
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PyObject *bco;
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long rc;
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if (ImageopDict == NULL) /* "cannot happen" */
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return 1;
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if (bcos == NULL) {
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/* cache string object for future use */
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bcos = PyString_FromString("backward_compatible");
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if (bcos == NULL)
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return 1;
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}
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bco = PyDict_GetItem(ImageopDict, bcos);
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if (bco == NULL)
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return 1;
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if (!PyInt_Check(bco))
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return 1;
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rc = PyInt_AsLong(bco);
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if (PyErr_Occurred()) {
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/* not an integer, or too large, or something */
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PyErr_Clear();
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rc = 1;
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}
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return rc != 0; /* convert to values 0, 1 */
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}
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static PyObject *
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imageop_crop(PyObject *self, PyObject *args)
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{
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@ -497,11 +544,11 @@ static PyObject *
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imageop_rgb2rgb8(PyObject *self, PyObject *args)
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{
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int x, y, len, nlen;
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Py_UInt32 *cp;
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unsigned char *cp;
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unsigned char *ncp;
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PyObject *rv;
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int i, r, g, b;
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Py_UInt32 value, nvalue;
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int backward_compatible = imageop_backward_compatible();
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if ( !PyArg_ParseTuple(args, "s#ii", &cp, &len, &x, &y) )
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return 0;
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@ -519,18 +566,19 @@ imageop_rgb2rgb8(PyObject *self, PyObject *args)
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for ( i=0; i < nlen; i++ ) {
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/* Bits in source: aaaaaaaa BBbbbbbb GGGggggg RRRrrrrr */
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value = *cp++;
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#if 0
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r = (value >> 5) & 7;
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g = (value >> 13) & 7;
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b = (value >> 22) & 3;
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#else
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r = (int) ((value & 0xff) / 255. * 7. + .5);
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g = (int) (((value >> 8) & 0xff) / 255. * 7. + .5);
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b = (int) (((value >> 16) & 0xff) / 255. * 3. + .5);
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#endif
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nvalue = (r<<5) | (b<<3) | g;
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*ncp++ = (unsigned char)nvalue;
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if (backward_compatible) {
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Py_UInt32 value = * (Py_UInt32 *) cp;
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cp += 4;
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r = (int) ((value & 0xff) / 255. * 7. + .5);
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g = (int) (((value >> 8) & 0xff) / 255. * 7. + .5);
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b = (int) (((value >> 16) & 0xff) / 255. * 3. + .5);
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} else {
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cp++; /* skip alpha channel */
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b = (int) (*cp++ / 255. * 3. + .5);
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g = (int) (*cp++ / 255. * 7. + .5);
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r = (int) (*cp++ / 255. * 7. + .5);
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}
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*ncp++ = (unsigned char)((r<<5) | (b<<3) | g);
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}
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return rv;
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}
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@ -540,10 +588,11 @@ imageop_rgb82rgb(PyObject *self, PyObject *args)
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{
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int x, y, len, nlen;
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unsigned char *cp;
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Py_UInt32 *ncp;
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unsigned char *ncp;
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PyObject *rv;
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int i, r, g, b;
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Py_UInt32 value, nvalue;
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unsigned char value;
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int backward_compatible = imageop_backward_compatible();
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if ( !PyArg_ParseTuple(args, "s#ii", &cp, &len, &x, &y) )
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return 0;
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@ -557,7 +606,7 @@ imageop_rgb82rgb(PyObject *self, PyObject *args)
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rv = PyString_FromStringAndSize(NULL, nlen*4);
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if ( rv == 0 )
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return 0;
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ncp = (Py_UInt32 *)PyString_AsString(rv);
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ncp = (unsigned char *)PyString_AsString(rv);
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for ( i=0; i < nlen; i++ ) {
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/* Bits in source: RRRBBGGG
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@ -570,8 +619,16 @@ imageop_rgb82rgb(PyObject *self, PyObject *args)
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r = (r<<5) | (r<<3) | (r>>1);
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g = (g<<5) | (g<<3) | (g>>1);
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b = (b<<6) | (b<<4) | (b<<2) | b;
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nvalue = r | (g<<8) | (b<<16);
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*ncp++ = nvalue;
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if (backward_compatible) {
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Py_UInt32 nvalue = r | (g<<8) | (b<<16);
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* (Py_UInt32 *) ncp = nvalue;
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ncp += 4;
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} else {
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*ncp++ = 0;
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*ncp++ = b;
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*ncp++ = g;
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*ncp++ = r;
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}
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}
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return rv;
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}
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@ -580,11 +637,12 @@ static PyObject *
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imageop_rgb2grey(PyObject *self, PyObject *args)
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{
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int x, y, len, nlen;
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Py_UInt32 *cp;
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unsigned char *cp;
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unsigned char *ncp;
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PyObject *rv;
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int i, r, g, b;
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Py_UInt32 value, nvalue;
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int nvalue;
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int backward_compatible = imageop_backward_compatible();
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if ( !PyArg_ParseTuple(args, "s#ii", &cp, &len, &x, &y) )
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return 0;
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@ -601,10 +659,18 @@ imageop_rgb2grey(PyObject *self, PyObject *args)
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ncp = (unsigned char *)PyString_AsString(rv);
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for ( i=0; i < nlen; i++ ) {
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value = *cp++;
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r = (value ) & 0xff;
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g = (value >> 8) & 0xff;
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b = (value >> 16) & 0xff;
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if (backward_compatible) {
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Py_UInt32 value = * (Py_UInt32 *) cp;
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cp += 4;
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r = (int) ((value & 0xff) / 255. * 7. + .5);
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g = (int) (((value >> 8) & 0xff) / 255. * 7. + .5);
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b = (int) (((value >> 16) & 0xff) / 255. * 3. + .5);
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} else {
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cp++; /* skip alpha channel */
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b = *cp++;
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g = *cp++;
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r = *cp++;
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}
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nvalue = (int)(0.30*r + 0.59*g + 0.11*b);
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if ( nvalue > 255 ) nvalue = 255;
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*ncp++ = (unsigned char)nvalue;
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@ -617,10 +683,11 @@ imageop_grey2rgb(PyObject *self, PyObject *args)
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{
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int x, y, len, nlen;
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unsigned char *cp;
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Py_UInt32 *ncp;
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unsigned char *ncp;
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PyObject *rv;
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int i;
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Py_UInt32 value;
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unsigned char value;
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int backward_compatible = imageop_backward_compatible();
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if ( !PyArg_ParseTuple(args, "s#ii", &cp, &len, &x, &y) )
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return 0;
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@ -634,11 +701,19 @@ imageop_grey2rgb(PyObject *self, PyObject *args)
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rv = PyString_FromStringAndSize(NULL, nlen*4);
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if ( rv == 0 )
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return 0;
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ncp = (Py_UInt32 *)PyString_AsString(rv);
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ncp = (unsigned char *)PyString_AsString(rv);
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for ( i=0; i < nlen; i++ ) {
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value = *cp++;
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*ncp++ = value | (value << 8 ) | (value << 16);
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if (backward_compatible) {
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* (Py_UInt32 *) ncp = (Py_UInt32) value | ((Py_UInt32) value << 8 ) | ((Py_UInt32) value << 16);
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ncp += 4;
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} else {
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*ncp++ = 0;
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*ncp++ = value;
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*ncp++ = value;
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*ncp++ = value;
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}
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}
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return rv;
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}
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@ -699,10 +774,10 @@ static PyMethodDef imageop_methods[] = {
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PyMODINIT_FUNC
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initimageop(void)
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{
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PyObject *m, *d;
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PyObject *m;
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m = Py_InitModule("imageop", imageop_methods);
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d = PyModule_GetDict(m);
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ImageopDict = PyModule_GetDict(m);
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ImageopError = PyErr_NewException("imageop.error", NULL, NULL);
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if (ImageopError != NULL)
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PyDict_SetItemString(d, "error", ImageopError);
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PyDict_SetItemString(ImageopDict, "error", ImageopError);
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}
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