Re: filter for jpeg can not use

[chuck c <bubbasnmp () gmail com>]

The JPEG dissector (
https://code.wireshark.org/review/gitweb?p=wireshark.git;a=blob;f=epan/dissectors/packet-jpeg.c
)
   1 /* packet-jpeg.c
   2  *
   3  * Routines for RFC 2435 JPEG dissection

is following RFC 2435 (https://tools.ietf.org/html/rfc2435) which specifies
width field:
3.1.5.  Width: 8 bits

   This field encodes the width of the image in 8-pixel multiples (e.g.,
   a width of 40 denotes an image 320 pixels wide).  The maximum width
   is 2040 pixels.

So the field in Wireshark is 8 bits with a max value of 255.

  72 static header_field_info hfi_rtp_jpeg_main_hdr_width JPEG_HFI_INIT = {
  73         "Width",
  74         "jpeg.main_hdr.width",
  75         FT_UINT8, BASE_DEC, NULL, 0,
  76         NULL, HFILL




On Fri, Jun 12, 2020 at 10:42 AM damker <damker () sina com> wrote:

> Filter "jpeg.main_hdr.width == 640" can not use, it hints that "640 too
> big for this field, maxinum".
> This field encodes the width of the image in 8-pixel multiples (e.g.,
> a width of 80 denotes an image 640 pixels wide).
> If I use "jpeg.main_hdr.width == 80", it means that the number of pixels
> is 80, and it didn't turn out to be what I wanted (I want that the number
> of pixels is 640)
> , it meight be a bug.
>
> ------------------------------
> damker
>
>
>
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