diff options
| -rw-r--r-- | converter/ppm/pcxtoppm.c | 38 | ||||
| -rw-r--r-- | doc/HISTORY | 3 |
2 files changed, 33 insertions, 8 deletions
diff --git a/converter/ppm/pcxtoppm.c b/converter/ppm/pcxtoppm.c index f06dd4e8..8341cf18 100644 --- a/converter/ppm/pcxtoppm.c +++ b/converter/ppm/pcxtoppm.c @@ -363,9 +363,25 @@ pcxPlanesToPixels(unsigned char * const pixels, unsigned int const planes, unsigned int const bitsPerPixel) { /*---------------------------------------------------------------------------- - Convert multi-plane format into 1 pixel per byte. + Unpack sub-byte sample values to yield one byte per pixel. + + As input, 'bitPlanes' is a row of the image. Each byte contains 8 samples, + one per bit. They are arranged in plane major, column minor order, e.g. + in a 100-column image, the Plane 1 samples of the Columns 0-8 are in + bitPlanes[100]. + + As output, each byte of 'pixels' is one pixel, in major order by column and + minor order by plane, e.g. in a 4-plane image, pixels[5] is the Plane 1 of + Column 1. + + 'bitsPerPixel' is the number of bits per sample, and must be 1. It's easy + to conceive how this subroutine should work with other numbers of bits per + sample, but it doesn't. -----------------------------------------------------------------------------*/ - unsigned int const npixels = (bytesPerLine * 8) / bitsPerPixel; + unsigned int const pixelCt = bytesPerLine * 8; + + unsigned int bitPlanesIdx; + /* Index into 'bitPlanes' of next byte to unpack */ unsigned int i; @@ -375,23 +391,29 @@ pcxPlanesToPixels(unsigned char * const pixels, pm_error("can't handle more than 1 bit per pixel"); /* Clear the pixel buffer - initial value */ - for (i = 0; i < npixels; ++i) + for (i = 0; i < pixelCt; ++i) pixels[i] = 0; + bitPlanesIdx = 0; /* initial value */ + for (i = 0; i < planes; ++i) { unsigned int const pixbit = (1 << i); + unsigned int pixelIdx; + /* Index into 'pixels' of next pixel to output */ + unsigned int j; - for (j = 0; j < bytesPerLine; ++j) { - unsigned int const bits = bitPlanes[j]; + for (j = 0, pixelIdx = 0; j < bytesPerLine; ++j) { + unsigned int const bits = bitPlanes[bitPlanesIdx++]; unsigned int mask; - unsigned int k; - for (mask = 0x80, k = 0; mask != 0; mask >>= 1, ++k) + for (mask = 0x80; mask != 0; mask >>= 1) { if (bits & mask) - pixels[k] |= pixbit; + pixels[pixelIdx] |= pixbit; + ++pixelIdx; + } } } } diff --git a/doc/HISTORY b/doc/HISTORY index 17c0b0f5..4a84359b 100644 --- a/doc/HISTORY +++ b/doc/HISTORY @@ -6,6 +6,9 @@ CHANGE HISTORY not yet BJH Release 11.09.00 + pcxtoppm: Fix wildly incorrect output for all multiplane + images. Broken in Netpbm 11.04 (September 2023). + pbmtoascii: fix bug: allows both -1x2 and -2x4. Always present (pbmtoascii existed in primordial Netpbm). |