tgl@zog.cs.cmu.edu (Tom Lane) (07/11/90)
I've been looking at some of the GIF image archives here and there on the net. I find that some of the images look just fine on my workstation, while others are visibly distorted: usually, compressed vertically by 20% or so. I presume that such images have been set up to look OK on IBM-PC EGA and similar displays, which have non-square pixels. However, the extent of the distortion seems to vary between files; maybe there are different pixel aspect ratios in common use? The GIF documentation that I have makes no mention of the question of pixel shape. Is there any recognized convention about whether a GIF image is set up for square or non-square pixels, and what the assumed pixel aspect ratio is in the latter case? -- tom lane Internet: tgl@cs.cmu.edu UUCP: <your favorite internet/arpanet gateway>!cs.cmu.edu!tgl BITNET: tgl%cs.cmu.edu@cmuccvma CompuServe: >internet:tgl@cs.cmu.edu
bli@aludra.usc.edu (I are a college student.) (07/20/90)
In article <9866@pt.cs.cmu.edu> tgl@zog.cs.cmu.edu (Tom Lane) writes: >I've been looking at some of the GIF image archives here and there on the >net. I find that some of the images look just fine on my workstation, while >others are visibly distorted: usually, compressed vertically by 20% or so. >I presume that such images have been set up to look OK on IBM-PC EGA and >similar displays, which have non-square pixels. However, the extent of the >distortion seems to vary between files; maybe there are different pixel >aspect ratios in common use? This may be totally unrelated to the discussion at hand, so please excuse the interuption. My Question: I have never seen the screen of a Sun close enough to look at the pixels on its display. Can someone please mail me the aspect ratio of a Sun display? I am trying to convert SunRasters to another format, and I need to know if I can _safely_ assume that all SunRasters have square pixels. ----- STRESS('stres)n: that confusion created when one's mind overrides the desire to choke the living daylights out of some jerk who really deserves it.
poynton@vector.Eng.Sun.COM (Charles A. Poynton) (07/26/90)
A college student <bli@aludra.usc.edu> writes in <10927@chaph.usc.edu>: > [Can I] assume that all SunRasters have square pixels? As long as I am alive and working at Sun, all Sun displays will have unity sample aspect ratio, a.k.a. square pixels. > Can someone please mail me the aspect ratio of a Sun display? By knowing that the pixels are guaranteed square, the display pixel counts determine the picture aspect ratio: 1152x900 gives a 1.28:1 picture. Current CRTs have a viewable area of 4:3 aspect ratio so an 1152x900 (1.28:1) or 1280x1024 (1.25:1) display does not quite fill the available width: these formats have wider left and right margins than top and bottom. There is currently a raging debate about "sample aspect ratio" in the HDTV standards community. HDTV is agreed to have a 16:9 picture aspect ratio (about 1.78:1). My proposal for digital representation is 1920x1080, just slightly under 2 Mpx, square pixels of course. Many "proponents" of advanced television production and transmission systems have system parameters inherited from NTSC and many have non-square pixels. C. ----- Charles A. Poynton Sun Microsystems Inc. vox 415-336-7846 2550 Garcia Avenue, MTV21-10 fax 415-969-9131 Mountain View, CA 94043 <poynton@sun.com> U.S.A. -----