Re: [Pfspd-users@sf.net] Cpfspd change proposal on aspect ratiobehaviour

[Bram R. <bra...@ph...>]

Dear all,

The changes as described below have been implemented.
Note however, that the behaviour of p_create_header() is not modified
since the SD image size still causes the default 4:3 aspect ratio.

>From the readme file:

- The display aspect ratio setting can now have value P_AS_WH,
  indicating that the intended aspect ratio of the diplay
  is equal to the width/height ratio in pixels. This value
  is an indication of square pixels as long as the width/height
  ratio remains the same.
- Function p_create_ext_header() can now be called with
  value P_UNKNOWN_ASPECT_RATIO in the ratio parameter.
  This causes an automatic 16:9/4:3 selection.
  See cpfspd.h for details on the selection algorithm.

>From the cpfspd.h file:

  The pfspd file format supports a display aspect ratio setting.
  This setting defines the intended shape of the physical display
  used by the image.
  Function p_create_ext_header() accepts the aspect ratio as input
  parameter. The default aspect ratio setting is 4:3 when using
  function p_create_header().
  When using function p_create_ext_header() with ratio argument
  P_UNKNOWN_ASPECT_RATIO, then an automatic aspect ratio is choosen,
  according to:
  - For image size HDi and HDp: the aspect ratio is always 16:9.
  - For other image sizes (SD, CIF, QCIF):
    If the number of pixels per line is larger than the default value,
    then the aspect ratio is 16:9; otherwise, the aspect ratio is 4:3.

  Notes:
  1) Aspect ratio setting P_AS_WH indicates that the aspect ratio
  of the display equals the aspect ratio of the image width/height.
  This is equal to a "square pixel" setting. However, after scaling or
  cropping (i.e. changing the width and/or height of the image) then
  the application is responsible to maintain a square pixel setting,
  since the pfspd file stores the display aspect ratio (without
  any knowledge on the pixel aspect ratio).
  This can be achieved by calling p_mod_aspect_ratio().


Developers, please update your sandboxes.

Regards, Bram.

--
A.K. (Bram) Riemens
Principal Scientist, DSP group, Philips Research
Office: WO-p-94, Postbox WO02
High Tech Campus 36 (WO), 5656 AE Eindhoven, The Netherlands
Tel: +31 40 27 43833, Fax: +31 40 27 44675
E-mail: bra...@ph...








Bram Riemens 
Sent by:
pfs...@li...
26-06-2006 11:50

To
pfs...@li...
cc
Frank van Heesch/EHV/RESEARCH/PHILIPS@PHILIPS
Subject
[Pfs...@sf...] Cpfspd change proposal on aspect   ratiobehaviour
Classification








Hi all, 

Frank van Heesch triggered a disussion on the use of the display 
aspect ratio in cpfspd and related tools. 
This email outlines a CPFSPD change proposal. 


Current situation 

Cpfspd supports two display aspect ratios: 4:3 and 16:9. 
These are both commonly used in current TV standards. 
For several reasons, current tools and files do not use the 16:9 
values properly - the 4:3 default is almost always used. 
Consequently, almost every file is tagged as 4:3. 
Up till now, we did not really pay attention to the aspect ratio. 
Frank pointed out some good reasons to pay attention: 
- Frank is working on an application that needs to use the information 
- Wrong values are confusing 


Requirements 

- Appropriate defaults for aspect ration 
  (so most tools will "automatically" set correct aspect ratio values). 
- Support for "square pixel" aspect ratio 
  (since many pfspd files contain a graphics image) 


Boundary conditions 

- Minimal or no change in API. 
- Consistency with current API semantics. 
- No change in pfspd file format. 
  The file format describes only a __display__ aspect ratio (or image 
aspect ratio). 
  Hence, a "square pixel" aspect ratio is only valid for a certain image 
width/height 
  and cannot be preserved automatically over scaling operations. 


Propsed solution 

Both PV and PP will NOT be adapted. Main focus of these tools is 
visulisation 
of the pixels. A deformation of the image aspect ratio is acceptable and 
clearly 
favourable over scaling (requiering filtering with two main disadvantages: 
original 
pixel values are lost and slowdown due to the extra calculations). 

cpfspd.h 
- Add P_AS_WH to pT_asp_rat. 

cpfspd_get.c / p_get_aspect_ratio() 
- Add P_AS_WH; use largest common divider from image width/height to check 
this value. 

cpfspd_mod.c / p_mod_aspect_ratio() 
- Add P_AS_WH; use largest common divider from image width/height to 
calculate this value. 
Note that this is only "square pixel" for the current width/height 
setting. 

cpfspd_hdr.c / p_set_header_values()                internal function 
- Add P_AS_WH as parameter value; use largest common divider from image 
width/height 
to calculate this value. 
- Add P_UNKNOWN_ASPECT_RATIO to serve as "default" parameter value 
to enable automatic setting depending on pT_size values: 
P_4_3  for   P_SD, P_CIF,  P_QCIF 
P_16_9 for P_HDp,  P_HDi 

cpfspd_hdr.c / p_set_stream_header_values()                internal 
function 
As p_set_header_values(). 

cpfspd_hdr.c / p_create_header() 
- Pass P_UNKNOWN_ASPECT_RATIO (not P_4_3) to p_create_ext_header(). 

cpfspd_hdr.c / p_create_ext_header() 
- No code change, funcionality changed by underlaying 
p_set_header_values() / p_set_stream_header_values(). 


Non-cpfspd issues 

Cpfspd application/tools that change image size (scale, border, crop, 
trim) need to handle the 
aspect ratio explicitely. If input file has P_AS_WH then output must be 
explicitely set 
at P_AS_WH to retain the "square pixel" property. 


Your comments / suggestions / improvements are appreciated. 

Regards, Bram. 

PS: Frank, please subscribe to the relevant mailing list via 
https://sourceforge.net/mail/?group_id=137382

--
A.K. (Bram) Riemens
Principal Scientist, DSP group, Philips Research
Office: WO-p-94, Postbox WO02
High Tech Campus 36 (WO), 5656 AE Eindhoven, The Netherlands
Tel: +31 40 27 43833, Fax: +31 40 27 44675
E-mail: bra...@ph... Tomcat but need to do more? Need to 
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