Hello Jose and all, >But I wonder...isn't it encoded that way, with those coeffcients from >the image source? >Because doing it twice will certainly "distort" the image. >There are two types of pictures Colour or B&W (grey in fact):
* "Pic:320x256C;" for example for a color picture of 320x256 dimension whose transmission will last 320x256x3x0,001=246 sec, There you send the picture in 3 colour plans: Red, Green and Blue * "Pic:320x256;" for example for a black and white picture of 320x256 dimension whose transmission will last 320x256x1x0,001=82 sec. There you transform the picture in 3 colour plans (Red, Green and Blue) to a picture in grey nuances. I understand that normally the formula might be Grey level = 0,333 x Red level + 0,333 x Green level + 0,333 x Blue level But if you see the result, it is not very nice (a bit too black without contrast). So it has been determined the magic formula Grey level = 0,30 x Red level + 0,59 x Green level + 0,11 x Blue level Of course, it is only a physiological formula, but universaly used. 73 Patrick ----- Original Message ----- From: Jose A. Amador To: digitalradio@yahoogroups.com Sent: Thursday, January 25, 2007 9:38 PM Subject: Re: [digitalradio] Why MSFK images can be noisy? Patrick Lindecker wrote: > Hello Jose, > > MFSK pictures are analog SSTV not digital SSTV. > > Here are the MFSK SSTV specifications (from the Multipsk help) > > 73 Patrick > > *SSTV in MFSK16* > > Created by : Nick Fedoseev (UT2UZ) and Denis Nechitailov (UU9JDR) in > 2003 > > _Description_ : > > It is a SSTV mode without transmission of a synchronization ray, in > color or in black and white mode, where the picture may be > transmitted among MFSK16 text. The picture format is not fixed as in > classical SSTV but variable (limited to small pictures). Multipsk > proposes to use the standard "320x256" to take advantage of the SSTV > "workshop" and the stored SSTV pictures. The band of frequencies used > is 234,375 Hz (15 x 15,625 Hz), which is the width between extreme > peaks of a MFSK16 transmission. The duration of a pixel is exactly 1 > ms. In color mode, the colors are transmitted in the following order: > Red, Green, Blue. In black and white mode, the black color > corresponds to the lower frequency and the white color to the higher > frequency. > > To be recognized, the picture must be MFSK16 prefixed by: > > * "Pic:320x256C;" for example for a color picture of 320x256 > dimension whose transmission will last 320x256x3x0,001=246 sec, * > "Pic:320x256C;" for example for a black and white picture of 320x256 > dimension whose transmission will last 320x256x1x0,001=82 sec. > > Note: on this program, for a better appearance, the grey level is > computed according to a "physiological" formula: Grey level = 0,30 x > Red level + 0,59 x Green level + 0,11 x Blue level Thank you, Patrick. It is analog after all. But I wonder...isn't it encoded that way, with those coeffcients from the image source? Because doing it twice will certainly "distort" the image. Once (early 90's) I had to do so to reproduce gray scales on a B/W monitor and a CGA video card. It certainly worked and gray scales were more pleasant. Now that old TV monitor is history... The image source was the computer itself, running in MSDOS, text mode. But I would not apply it to an image coming from a photo...of course, I still have many doubts on how is it done on MFSK. Jose, CO2JA
