/**
* @brief read a PNG file into a 8bit integer array, converted to gray
*
* See read_png_u8() for details.
*/
unsigned char *read_png_u8_gray(const char *fname, size_t * nx, size_t * ny)
{
size_t nc;
unsigned char *img;
/* read the image */
img = (unsigned char *) read_png_raw(fname, nx, ny, &nc,
PNG_TRANSFORM_STRIP_ALPHA,
IO_PNG_U8);
if (NULL == img)
/* error */
return NULL;
if (1 == nc)
/* already gray */
return img;
else
{
/* convert to gray */
unsigned char *ptr_r, *ptr_g, *ptr_b, *ptr_gray, *ptr_end;
/*
* RGB->gray conversion
* Y = (6969 * R + 23434 * G + 2365 * B)/32768
* integer approximation of
* Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
*/
ptr_r = img;
ptr_g = img + *nx * *ny;
ptr_b = img + 2 * *nx * *ny;
ptr_gray = img;
ptr_end = ptr_gray + *nx * *ny;
while (ptr_gray < ptr_end)
*ptr_gray++ = (unsigned char) (6969 * *ptr_r++
+ 23434 * *ptr_g++
+ 2365 * *ptr_b++) / 32768;
/* resize and return the image */
img = (unsigned char*) realloc(img, *nx * *ny * sizeof(unsigned char));
return img;
}
}
unsigned char *read_png_u8_rgb(const char *fname, size_t * nxp, size_t * nyp)
{
size_t nc;
unsigned char *img;
/* read the image */
img = (unsigned char *) read_png_raw(fname, nxp, nyp, &nc,
PNG_TRANSFORM_STRIP_ALPHA,
IO_PNG_U8);
if (NULL == img)
/* error */
return NULL;
if (3 == nc)
/* already RGB */
return img;
else
{
/* convert to RGB */
unsigned char *ptr_r, *ptr_g, *ptr_b, *ptr_end;
/* resize the image */
img = realloc(img, 3 * *nxp * *nyp * sizeof(unsigned char));
/* gray->RGB conversion */
ptr_r = img;
ptr_end = ptr_r + *nxp * *nyp;
ptr_g = img + *nxp * *nyp;
ptr_b = img + 2 * *nxp * *nyp;
while (ptr_r < ptr_end)
{
*ptr_g++ = *ptr_r;
*ptr_b++ = *ptr_r++;
}
return img;
}
}
/**
* @brief read a PNG file into a 32bit float array
*
* The array contains the deinterlaced channels.
* 1, 2, 4 and 8bit images are converted to float values
* between 0. and 1., 3., 15. or 255.
* 16bit images are also downscaled to 8bit before conversion.
*
* @param fname PNG file name
* @param nx, ny, nc pointers to variables to be filled with the number of
* columns, lines and channels of the image
* @return pointer to an allocated unsigned char array of pixels,
* or NULL if an error happens
*/
float *read_png_f32(const char *fname, size_t * nx, size_t * ny, size_t * nc)
{
/* read the image as float */
return (float *) read_png_raw(fname, nx, ny, nc,
PNG_TRANSFORM_IDENTITY, IO_PNG_F32);
}
