skinner@unc.cs.unc.edu (Andrew Skinner) (01/31/89)
I would like to be able to look at the results of work when I am at home. A reasonable approximation would do, so I'd like to be able to convert picture files produced at school to HAM mode pictures, to be displayed by standard programs. Does anyone have any free source code I could use to convert (8 bit greyscale) images to HAM mode? I'm sure it would be an interesting and useful project for me, but I just don't have time. Obviously, something more general (24 bit RGB to HAM) would be nice, but most of our stuff currently is greyscale, so I'll take what I can get. I can do an ftp if there is something on line. My email address is: skinner@unc.cs.unc.edu Thanks, andy skinner
mp1u+@andrew.cmu.edu (Michael Portuesi) (01/31/89)
skinner@unc.cs.unc.edu (Andrew Skinner) writes: > Does anyone have any free source code I could use > to convert (8 bit greyscale) images to HAM mode? There is no need to use HAM mode for greyscale images. The Amiga display hardware can only generate 16 shades (4 bits) of grey, which can be displayed simultaneously in any resolution without using HAM. Better for you would be a program that converts 8 bit greyscale to 4 bit greyscale, and saves the results in IFF. Also, by not using HAM mode, you can display the pictures in high resolution, which is 640x400 versus the maximum 320x400 that HAM mode offers. -- Michael Portuesi / Information Technology Center / Carnegie Mellon University INET: mp1u+@andrew.cmu.edu / BITNET: mp1u+@andrew UUCP: ...harvard!andrew.cmu.edu!mp1u+ "I'm very sorry, Master, but that WAS the backup system" -- Slave
skinner@pooh.cs.unc.edu (Andrew Skinner) (02/01/89)
In article <6432@thorin.cs.unc.edu> skinner@unc.cs.unc.edu (Andrew Skinner) writes: > >A reasonable approximation would do, so I'd like to be able to convert >picture files produced at school to HAM mode pictures, to be displayed >by standard programs. Does anyone have any free source code I could use >to convert (8 bit greyscale) images to HAM mode? I'm sure it would be an The responses I have gotten (thanks) all tell me that I only have 16 shades of grey, so HAM won't help. I know that. My own question is whether it would be better to have some near-grey colors in between grey shades (using HAM--I know they wouldn't really be grey), or to just use the 16 I have. The second is easier, and I wouldn't have considered it without the replies I got. But I'd like to get as much color resolution as I can, since I want to look at high quality 3D renderings. I can probably do the second, given time to do it, without problem. I can do the first, too, given HAM docs and, again, time. (I'm not a graphics beginner.) What I would like is similar code, that I can use without taking lots of time from the work that produces the pictures I want to see. The other thing I learned from the responses was that HAM didn't give me full resolution. I either didn't know that or had forgotten. I think I will try to just use the 4 bits I've got, for now. Thanks again, andy skinner skinner@unc.cs.unc.edu
c60a-1fy@web-2a.berkeley.edu (Anon) (02/01/89)
In article <6432@thorin.cs.unc.edu> skinner@unc.cs.unc.edu (Andrew Skinner) writes: > >I would like to be able to look at the results of work when I am at home. >A reasonable approximation would do, so I'd like to be able to convert >picture files produced at school to HAM mode pictures, to be displayed >by standard programs. Does anyone have any free source code I could use >to convert (8 bit greyscale) images to HAM mode? I'm sure it would be an Whatta you want ham for? There are only 16 shades of grey in the palette anyway, you ham won't gain you anything. Just use the 4 msb's and convert to a 4-plane hires picture.
dale@boing.UUCP (Dale Luck) (02/01/89)
In article mp1u+@andrew.cmu.edu (Michael Portuesi) writes: #skinner@unc.cs.unc.edu (Andrew Skinner) writes: #> Does anyone have any free source code I could use #> to convert (8 bit greyscale) images to HAM mode? # #There is no need to use HAM mode for greyscale images. The Amiga #display hardware can only generate 16 shades (4 bits) of grey, which can be #displayed simultaneously in any resolution without using HAM. Better #for you would be a program that converts 8 bit greyscale to 4 bit #greyscale, and saves the results in IFF. # Not completely true, by using the mono output of the 500 or the 2000 you can get closer to few thousand shades of grey. The rgb values are weighted differently to produce a single luminance value. It is probably close to .587g .299g and .11b or something like that. -- Dale Luck GfxBase/Boing, Inc. {uunet!cbmvax|pyramid}!amiga!boing!dale
mikes@lakesys.UUCP (Mike Shawaluk) (02/01/89)
In article <19763@agate.BERKELEY.EDU> c60a-1fy@web-2a.berkeley.edu (Anon) writes: >In article <6432@thorin.cs.unc.edu> skinner@unc.cs.unc.edu (Andrew Skinner) writes: >> >>I would like to be able to look at the results of work when I am at home. >>A reasonable approximation would do, so I'd like to be able to convert >>picture files produced at school to HAM mode pictures, to be displayed >>by standard programs. Does anyone have any free source code I could use >>to convert (8 bit greyscale) images to HAM mode? I'm sure it would be an > >Whatta you want ham for? There are only 16 shades of grey in the palette >anyway, you ham won't gain you anything. Just use the 4 msb's and convert >to a 4-plane hires picture. This reply to Andrew's original message, and a few others, have pointed out that HAM won't buy anything in regard to viewing grey-scale images, since there are only 16 possible shades of grey that can be generated using the Amiga's 4096 color pallette. However, Andrew didn't say (at least I didn't SEE him say it; I don't have the original article, only replies to his posting) what the resolution of the 8-bit grey scale images was. If they are less that 640 by 400, then additional grey shade can be generated by dithering. I won't go into a technical discussion of it here, because I'm not that well-versed on the technical details, but only on the fact that it should work, provided that the images being imported are of a lower pixel resolution that 640 x 400. I should mention that you probably wouldn't be able to get 256 levels of grey by dithering, even if you went to 320 by 200 effective resolution, and that you'd probably get some flicker because of the interlace, although if the images are smoothly shaded, the flicker should be pretty minimal. Would someone with the appropriate technical background on graphics and dithering please fill in the gaps in what I've said above (i.e, tell me if I'm full of $#!+ or not...) -- - Mike Shawaluk ...!uunet!marque!lakesys!mikes
waynet@mongo.uucp (Wayne Thompson) (02/04/89)
In article <613@boing.UUCP> dale@boing.UUCP (Dale Luck) writes:
Not completely true, by using the mono output of the 500 or the 2000 you
can get closer to few thousand shades of grey. The rgb values are weighted
differently to produce a single luminance value. It is probably close
to .587g .299g and .11b or something like that.
--
Dale Luck GfxBase/Boing, Inc.
{uunet!cbmvax|pyramid}!amiga!boing!dale
Does anyone have have the actual weighting values?
Waynedan@ivucsb.UUCP (Dan Howell) (02/12/89)
Another thing you might consider is dithering. Add a random number between -8 and +8 to the original 8 bit value, making sure not to overflow or underflow, and take the 4 MSBs of the result. This should give a result which will have an apparent grey-scale resolution much higher than 4 bits, and will also eliminate the "contouring" effect of short-word-length quantization. -- Dan Howell <...!pyramid!nessus!ivucsb!dan> <dan@ivucsb.UUCP> -- * Note new address path. Do not use comdesign, use nessus instead. *
rokicki@polya.Stanford.EDU (Tomas G. Rokicki) (02/13/89)
If you're going to add that random number, accumulate the errors and apply to the next bit so you don't get too much of grain. -tom
elbaum@reed.UUCP (Daniel Elbaum) (02/13/89)
In article <338@lakesys.UUCP> mikes@lakesys.UUCP (Mike Shawaluk) writes: >In article <19763@agate.BERKELEY.EDU> c60a-1fy@web-2a.berkeley.edu (Anon) writes: >>In article <6432@thorin.cs.unc.edu> skinner@unc.cs.unc.edu (Andrew Skinner) writes: >>> >>>I'd like to be able to convert picture files produced at school to HAM >>>mode pictures, to be displayed [as monochrome images]. >> >>There are only 16 shades of grey in the palette anyway, [so] ham won't >>gain you anything. > >HAM won't buy anything in regard to viewing grey-scale images >[but] additional grey shade can be generated by dithering. If your image is 320 x 200, you can get 60 shades of grey. Allocate a hi-res screen, and use a 2 x 2 pixel square (call it a tetrad) for each pixel in the original image. Each element of the tetrad can take on any of 16 shades of grey. Varying the shade of one tetrad element (tetrel?) would result in a small incremental change in the shade of the whole tetrad. To the eye (I've tried this) the pixels within the tetrad disappear, so that the smallest apparent element of the picture is the tetrad rather than the pixel. It's like building four stacks of coins so that they're all about the same height. If you have 64 coins and can't put more than 16 in a single stack, you start by laying down one coin, then one beside it, then one below the first, then one below the second, so you have a square. Then repeat the process, so eventually you have a 2 x 2 square of coins 16 coins deep. Each time you put down a new coin, you increase the total number of coins by one. But you don't get 64 shades of grey on the screen, since you can't have a zero-bit-plane display. In other words, you really only have 15 coins for each stack. Since you get four increments in tetrad value for each pixel value, you end up with 60 shades of grey. I used this technique to display character-graphics pictures (you know, the pinups made up of ASCII characters) with very good results. Resolution does suffer, but the shading turns out nicely. -- : Daniel Elbaum Responsible for all : tektronix!reed!elbaum disclaimed postings : elbaum@reed.bitnet