The Very Best of Atari Inside

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Text File | 1994-10-25 | 17.3 KB | 383 lines

Atari ST/E PhotoChrome ---------------------- Concept, Design and Programming by Douglas Little. (C) 1992-94 Black Scorpion development. You are now the proud owner of the PhotoChrome graphics card emulator. It is the only one of its type currently available for the Atari ST and is capable of out-performing most other screen modes including the infamous HAM and HalfBrite displays on the Commodore Amiga. It's basic specification is the ability to load many IFF formats, 24-Bit True colour screens (16 million colours), GIF files and VidiChrome digitised 'RGB' colour separations (4096 colours) before converting to one of six powerful screen modes. *---------------------------------------------------------------------* THE 6 CONVERSION MODES ---------------------- The six screen modes are... 1. Spectrum 512 > 42/45 cols per scanline from 512 on an ST or STE. 2. Spectrum 4096 > 42/45 cols per scanline from 4096 on an STE. 3. PCS-ST > 48 colours per scanline from 512 on an ST or STE. 4. PCS-STE > 48 colours per scanline from 4096 on an STE. 5. Super HAM > A full 4096 colours out of 4096 on an ST or STE. 6. STE PhotoChrome > 19200 colours out of 32768 on an STE. Modes 1 and 2 are basically real Spectrum-512 files. They are not compressed, but Spectrum can do this if you need it. STE mode seems to handle pictures better than I had expected, since with such a large palette the colour assignments tend to be used up twice as quickly. Modes 3 and 4 are my own custom versions of the Spectrum display. They both have a few extra colours to play with, filling up the streaks and dots Spectrum can often leave behind. This is my own 'PCS' format (PhotoChrome Screen) and uses the best of 2 compression methods. Modes 5 and 6 are actually impossible, so just accept they work and don't ask too many questions! SUPER HAM is an emulation of the Hold And Modify mode normally exclusive to the Commodore Amiga. After some experimentation with my own Amiga, I found that HAM is not actually as capable of displaying some of the more detailed colour images (especially with high levels of contrast or lots of sharp lines) and so renamed my own format 'SUPER HAM'. Many HAM pictures are of course better as they have many more colours per line, but have to smudge and blend to obtain them. PHOTOCHROME is only available when the source picture contains in excess of 4096 colours (i.e. true-colour 16M colour pictures), and then only to STE owners. However, if you do have an STE and some TGA files knocking about then you are in for a treat indeed! Eat your heart out, VGA! This is the most powerful mode available short of a real Graphics card, with 19200 colours on-screen at once from a largish palette of 32768! (15-bit colour). The picture requires two conversion passes, but is well worth the wait! N.B. Pictures saved out as Super HAM or PhotoChrome tend to be anywhere from large to enormous, even with fancy compression. Bear this in mind when testing out the hatched and fractal stippling options! (Check out PCSVIEW.DOC for info on better compression...) *---------------------------------------------------------------------* FEARURES -------- 1> STIPPLING. (COLOUR REDUCTION ONLY) Generally, if the source picture holds more colours than the destination format (i.e. TGA > SPU) then you are allowed stippling. The three options are CLEAN - just leave the picture as it is, HATCHED - use levels of hatching to make up in-between colours and FRACTAL - the weird one. This uses fractal numbers to highlight/leave each pixel on the screen, the result being that graduated colours look more obvious but you get a weird 'oil-painting' effect. It really only works well in PhotoChrome and super-HAM modes. 2> ERROR/FLICKER FREE. (SUPER HAM/PHOTOCHROME ONLY) Error-free mode makes a better job of mega-colourful pictures but is not normally needed (a sort of last-resort). 'Flicker-free' should be used where available, the only problem being that it chews through the colour tables at an alarming rate (keep an eye on TARGA screens). N.B. STE PhotoChrome mode is fixed at ERROR-FREE in 60Hz, since flicker is minimal with such a large palette, and requires as many colours as it can get. FLICKER-FREE mode CAN sometimes reduce the quality of the screen in extreme cases... 3> 50/60 Hz MODES. (SUPER HAM and QRT PICTURES ONLY) Basically, everything runs at 50Hz, with a couple of exceptions. QRT/DKB pictures tend to have a 60Hz aspect ratio (not fixed but the option is there) causing the screen to look squashed at 50Hz. Also, PHOTOCHROME mode looks best at 60Hz anyway, so it is left as the default frequency. 60Hz also helps when 'flicker-free' option has been avoided for accuracy. To change the default, click on the 50Hz button. All screens will now run at 50Hz regardless of how they might look. To switch modes while viewing the picture, hit the '*' key. 4> SPECTRUM OPTIONS. Spectrum 512 does not use all of it's available colours. Colour 0 (background colour) is always black and colour 15 is reserved for drawing and for the mouse pointer etc. leaving 14 variable colours for use in the picture. There are 3 palette changes per line meaning (16-2)*3 or 42 cols available for alteration on each individual scanline of the screen. The 'LEGAL COLOURS' option uses just these colours. The 'ALL COLOURS' option however releases colour 15 for use, meaning (16-1)*3 or 45 cols per line. The only disadvantage is that Spectrum will crack up if you try to load them in. Any pixels using colour 15 will turn bright orange and look a right mess. You have been warned... (N.B. slideshows should display these pictures no probs.) *---------------------------------------------------------------------* LIMITATIONS ----------- Hmmm, I'm not sure there are any, really.. No, seriously, there are a few bits you should know about before creating slideshows full of pretty pictures! *---------------------------------------------------------------------* 1> TGA's *---------------------------------------------------------------------* TARGA images are common on the Falcon and PC machines, as these tend to be capable of true-colour to some extent (PC). They can be of any width or height (above or below 320*200) and will be centred on the screen with a black border if they are smaller. If you use the 'flicker- free' option (SUPER HAM only) some loss of detail or palette-errors might occur on very complex pictures. To avoid this you may have to use the 'error-free' mode instead (at 60Hz there is very little flicker anyway). To cut down any flicker you may still see, reduce the contrast setting on your monitor. Older versions of PChrome will only load one type of targa file, and did so VERY slowly... The latest version loads around 12 variations - including 16-bit and compressed types. They can now be larger than the screen, and in upside-down format too. *---------------------------------------------------------------------* 2> RAW's *---------------------------------------------------------------------* See TARGA files above - RAW's are almost identical to one of the TARGA variants. *---------------------------------------------------------------------* 3> GIF's *---------------------------------------------------------------------* The program can load GIF's of any height or width and will offer the option to either squash the picture, or select a 320*200 zone. 320*200 GIF's will bypass this stage. To select a zone, use the arrow-keys and 'SPACE' when satisfied. *---------------------------------------------------------------------* 4> IFF's *---------------------------------------------------------------------* The program can load ILBM IFF's of any height or width but will crop them to 320*200 (a later version will contain squash/interlace options). All of the Amiga pictures I fed it looked identical to the originals, with the exception of a few strange res-sizes. No significant loss of colour or detail has been detected (HalfBrite 64-colour IFF's and 4-bit HAM's are now supported properly). *---------------------------------------------------------------------* 5> RGB's *---------------------------------------------------------------------* VidiChrome RGB screens suffer from very few limitations. Generally you should choose the 'flicker-free' option all the time and if you spot dots/errors on the screen (rare) you can resort to 60Hz and 'error-free' mode. *---------------------------------------------------------------------* 6> DIFFERENT PROCESSORS. *---------------------------------------------------------------------* Although Mega-STE's run at 16Mhz & cache, this can be disabled. PChrome now switches to 16Mhz+cache for image conversion and back to 8Mhz for display. The machine is returned to it's original state on quitting. PhotoChrome now RUNS on a 68030, but this chip is so different from the 68000 in speed even at 8Mhz, that the display code will not produce a picture. You will get a mess. (this does not stop you making an image and saving it out...) *---------------------------------------------------------------------* 7> SYNC PROBLEMS. *---------------------------------------------------------------------* It came to my attention some time ago that both Spectrum-512 and GFA Raytrace suffered from video-synchronisation problems. This caused very irritating little dots or vertical lines to appear from time to time and totally ruin the effect of the picture. It was also very embarrasing when trying to show off the ST's capabilities to other members of the computer world (i.e. Amiga-users). These programs are supplied with a 'SYNC.PRG' which, contrary to many peoples beliefs does sod-all to fix the problem. All it does is TELL you whether your ST is READY to display a picture or NOT, having no effect on the machine at all. The only way to rectify a 'no-sync' situation is to TURN OFF and reboot, resetting the video-clock hardware and hopefully reversing the situation. Generally it takes a few tries before success, and although I have seen a few ST's that ALWAYS boot up properly, the effect on STE's is generally quite bad (just try to merge a colour digitised picture in 4096 colour mode in VidiChrome and you'll probably see what I mean). Anyway, Since our own display code incorporates similar colour- switch techniques, PhotoChrome was initially prone to this bugging effect. After a lot of work and an equal amount of problems it has been solved, and as far as I know, is rectified on all ST's and STE's. All pictures saved out from PhotoChrome (including Spectrum-512/4096) are 'immunised' against sync problems, regardless of which slideshow program you choose to display them (they even load into Spectrum itself! Although if you mess about with the picture, Spectrum will re- assign the colours and destroy the immunised structure of the screen. *---------------------------------------------------------------------* SAVING A PICTURE ---------------- To save a screen, hit 'RETURN' or 'S' once it has been converted and is being displayed. The file will take a few seconds to compress before giving you a file selector. The program will check diskspace prior to saving the screen. To switch 50/60 Hz on the same screen, hit the '*' key. This will be recorded into the file for displaying in the slideshow. While selecting a part of a GIF picture, use the arrow keys and 'SPACE' when done. *------------------------------------------------------------------------* SHAREWARE THEORY -------------------------- (or, at least, Dug's View!) -------------------------- If you know what Shareware is, then you can skip the next 500 odd bytes of text and read the next paragraph instead. The idea behind Shareware is actually quite simple... Someone writes a program and gives it to someone, they either dislike it, like it or love it. The people who dislike it don't use the thing, and therefore certainly don't pay for it. Of the ones who do like the program, MOST will feel it is worthwhile paying for, and SOME will actually make donations to the author. Of the people who really like it, most will probably make a donation, and will also recommend and LEGALLY spread it to their friends, helping the author even more. Basically, everybody's happy, although the whole thing does rely on one thing being present somewhere along the line, that being HONESTY. It is a risky thing to depend on the public's honesty to make a living, but in a situation like this, the usual motives for piracy are gone. Nobody can feel cheated by shareware, since you pay for the software alone and not the blurb normally supplied by the 'houses' with their 'spacious' packaging and price-upping ring-bound manuals. This does not mean I am against commercial software, but quite a lot of it is expensive cr*p... There is an attractive list of facts... 1 - It kills piracy, since you can't pirate something you're TRYING to spread anyway! Spreading actually helps shareware by bringing it to other people's attention. 2 - You don't need to spend money on advertising. If it's good, it will tend to get about on it's own. (A review or two always helps start the ball rolling!) 3 - Customers only pay for what they use, they CANNOT be conned or cheated into buying software which is no use. They get as much time to evaluate it as they like, hopefully resulting in a small donation to the author. *--------------------------------------------------------------------* * PhotoChrome and Shareware * *--------------------------------------------------------------------* This program was a lot of work, but I do think it was worthwhile. It's about time the ST started to antagonise the other machines normally hogging the world of fancy graphics and sound. Most of PhotoChrome was written during 1 month of intensive programming and testing and it would be nice to see some sort of return for my work. A donation of about £2.00 - £5.00 would suffice, and I am also anxious to know of peoples thoughts on the program. The more donations I recieve the more incentive I will have to continue with the series and produce updates. (Now almost certain) PhotoChrome is currently being used in the pruduction of a new commercial program called ChromaStudio-ST (provisional name) which is based on a cross between my forthcoming ChromaStudio-24 (Falcon) and PChrome itself. If anyone is thinking seriously of writing a rendering package for the ST/E machines, then please consider these screen formats as worthwhile for inclusion. There is nothing worse than having an exceptional package held back by a low-quality output such as 16-colours or a badly rastered screen! *------------------------------------------------------------------------* SOURCE ------ A new file format is absoultely no use without software to utilise it or available source for programmers to use themselves. It is also annoying when the only type of source available is an object or 'BIN' file instead of a listing which greatly limits what you can do with it, unless you set about disassembling it yourself. This, I think stems from programmers being paranoid about other people seeing their code and so, try to protect it by hiding it from others. This helps nobody. I have decided to supply the documented source for the PCSVIEW slideshow on disk for £5.00 (see the address at bottom of text) There is a need for the format to become a standard (like Spectrum) and therefore needs to be widely available to programmers. *-----------------------------------------------------------------------* * The interesting bit stops here, * *-----------------------------------------------------------------------* PCSVIEW SOURCE available from... Douglas Little 160 Goremire Road, Carluke, Lanarkshire Scotland. ML8 4PN. (please indicate 'PHOTOCHROME SOURCE' on the envelope for a quick reply!) *-----------------------------------------------------------------------* > Doug Little > Neil Stewart > Andy Younger > Nick Hesketh > Black Scorpion will return in force. Until then...