bytes per pixel in PPM format

Accelerated Computing CUDA CUDA Programming and Performance
1

Hi,
I want to ask for a clarification for how cuda/cutil handles images in PPM format. Below is the code from the SobelFilter example in the SDK. The g_Bpp variable ( in line 314 & 320 ) I believe is the Bytes Per Pixel count for the different image formats. For PGM files (line 309) it is set to 1, which is just ideal. But for PPM, it is set to 4 which is odd becuase the PPM format has only 3-byte representation, 1-blue,1-red,1-green. Can anyone here shed some light on this?

thanks,

309 if (!strcmp(&file[file_length-3], “pgm”)) {
310 if (cutLoadPGMub(file, &pixels, &w, &h) != CUTTrue) {
311 printf(“Failed to load image file: %s\n”, file);
312 exit(-1);
313 }
314 g_Bpp = 1;
315 } else if (!strcmp(&file[file_length-3], “ppm”)) {
316 if (cutLoadPPM4ub(file, &pixels, &w, &h) != CUTTrue) {
317 printf(“Failed to load image file: %s\n”, file);
318 exit(-1);
319 }
320 g_Bpp = 4;
321 } else