[FFmpeg-devel] lavc/pnm: Support signed pgm files from jasper

[Nicolas George]

Carl Eugen Hoyos (12020-04-25):
> Hi!
> 
> Attached patch allows reading the pgm file that jasper creates
> using the jpeg 2000 reference file p0_03.j2k as input.
> 
> Please comment, Carl Eugen

> From 5da97c417d66b1e840b1feae31f0852cf3755c39 Mon Sep 17 00:00:00 2001
> From: Carl Eugen Hoyos <ceffmpeg at gmail.com>
> Date: Sat, 25 Apr 2020 17:05:40 +0200
> Subject: [PATCH] lavc/pnm: Allow reading signed pgm values as written by
>  jasper.
> 
> ---
>  libavcodec/pnm.c    | 4 ++++
>  libavcodec/pnm.h    | 1 +
>  libavcodec/pnmdec.c | 2 +-
>  3 files changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/libavcodec/pnm.c b/libavcodec/pnm.c
> index b5c2881948..c9b9eb9ccd 100644
> --- a/libavcodec/pnm.c
> +++ b/libavcodec/pnm.c
> @@ -176,6 +176,10 @@ int ff_pnm_decode_header(AVCodecContext *avctx, PNMContext * const s)
>      if (avctx->pix_fmt != AV_PIX_FMT_MONOWHITE && avctx->pix_fmt != AV_PIX_FMT_MONOBLACK) {
>          pnm_get(s, buf1, sizeof(buf1));
>          s->maxval = atoi(buf1);

> +        if (s->maxval < 0) {
> +            s->maxval *= -1;
> +            s->jasper_signed = 1;
> +        }
>          if (s->maxval <= 0 || s->maxval > UINT16_MAX) {

The s->maxval <= 0 test here has become redundant.

I do not know if the patch itself is correct and wanted.

>              av_log(avctx, AV_LOG_ERROR, "Invalid maxval: %d\n", s->maxval);
>              s->maxval = 255;
> diff --git a/libavcodec/pnm.h b/libavcodec/pnm.h
> index 5bc0aad29f..2550cef92b 100644
> --- a/libavcodec/pnm.h
> +++ b/libavcodec/pnm.h
> @@ -30,6 +30,7 @@ typedef struct PNMContext {
>      uint8_t *bytestream_end;
>      int maxval;                 ///< maximum value of a pixel
>      int type;
> +    int jasper_signed;
>  } PNMContext;
>  
>  int ff_pnm_decode_header(AVCodecContext *avctx, PNMContext * const s);
> diff --git a/libavcodec/pnmdec.c b/libavcodec/pnmdec.c
> index dbcaef3884..6e5f5b6c3b 100644
> --- a/libavcodec/pnmdec.c
> +++ b/libavcodec/pnmdec.c
> @@ -168,7 +168,7 @@ static int pnm_decode_frame(AVCodecContext *avctx, void *data,
>              else if (upgrade == 1) {
>                  unsigned int j, f = (255 * 128 + s->maxval / 2) / s->maxval;
>                  for (j = 0; j < n; j++)
> -                    ptr[j] = (s->bytestream[j] * f + 64) >> 7;
> +                    ptr[j] = ((s->bytestream[j] - (s->maxval / 2 - 1) * s->jasper_signed) * f + 64) >> 7;
>              } else if (upgrade == 2) {
>                  unsigned int j, v, f = (65535 * 32768 + s->maxval / 2) / s->maxval;
>                  for (j = 0; j < n / 2; j++) {

Regards,

-- 
  Nicolas George
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