CRT emulation¶
CRT shaders, sharp pixels, black borders around the image—these are very divisive topics in emulation circles, and the default graphics settings of RML Amiga might not suit your preferences. That’s fine, we’re all a bit different. Rest assured, you can customise these settings to your liking, including turning off the CRT emulation altogether. But it’s worthwhile to understand the reasoning behind the defaults first before you change anything.
Out-of-the-box, RML Amiga emulates the output of a 15 kHz Commodore CRT monitor. Most people used their Amigas with such monitors in the 1980s and 90s (e.g., the iconic Commodore 1084S or the Philips CM8833-II])1. The default 3.0x scaling mimics the physical dimensions of such 14” CRTs rather closely on 24 to 27” widescreen desktop displays. Just grab a ruler and measure the diagonal of the image in an NTSC game; it will be about 13” (33 cm) on a 24” screen which is close to the diagonal of the viewable area on a typical 14” CRT.
So what, you might think. We have bigger and better monitors now, so why not make the best of them and let the image fill the screen completely? Well, because arguably that wouldn’t be the “best” thing to do.
From a normal 1 to 1.5-meter viewing distance, the relatively small screen size of a 14” monitor combined with the beneficial smoothing effects of CRTs produced an image that looked very smooth and strangely higher resolution than it really was. The CRT took off the edges of the “pixels” and added a subtle texture to the image (CRTs don’t have “pixels”, but that’s a longer story). The perceived quality of 320×200 Amiga games on Commodore monitors rivalled the experience of 640×480 games on much sharper PC CRT monitors. Sure, the Amiga’s image was a bit blurrier and lacked fine detail, but it was nowhere near the extreme blockiness of how PC monitors presented 320×200 content! People moving on from the Amiga to the PC in the 1990s often complained about low-resolution pixel art suddenly looking overly blocky on their 14–15” PC monitors.2
Let me stress this again: 320×200 content on the Amiga was smooth, not blocky as on the PC! On well-made art, the “pixels” literally melted away; you did not see jagged stairstep edges but smooth curves!
(click on the image to enlarge it)
That’s all good and well, but some games still look subjectively better with the graphics slightly enlarged. For example, I like playing Pinball Dreams with 3.5x scaling so it almost completely fills the screen; it’s just more immersive for me that way. So by all means, feel free to to adjust the image size depending on your display size, viewing distance, and personal preference. You might also want to use different scaling factors for different games. The Customising your setup section shows you how to do that.
Be aware, however, that as you start deviating from the “canonical” 14” CRT image size (3.0x scaling factor), you will start seeing the “pixels”. The beneficial blur of the CRT emulation will also be enlarged, resulting in a subjectively less sharp-looking image. You can offset this by using the “sharp” variants of the shaders; these will reduce the blurriness substantially, but at the expense of the beneficial smoothing effects—the pixels will start looking blockier. Moreover, the scanlines will be more apparent at higher scaling factors, too, especially with the NTSC shader. You might want to force the PAL shader even in NTSC games to mitigate this as that renders more “densely packed” scanlines.
(click on the image to enlarge it)
As you can see, deviating from the canonical 14” CRT image size is all about tradeoffs. Even on real CRT monitors, the experience is not the same on larger 17” to 21” displays. You just need to pick what’s more important to you: authenticity and image quality, or image size and getting rid of the “black borders”.
This is certainly a fascinating topic; you can read more about it in my article that describes the CRT emulation setup of RML Amiga in detail.
-
The most popular Amiga model ever, the Amiga 500, had built-in RGB output but no aerial RF or composite connectivity to hook it up to a TV. There was a composite-compatible monochrome connector labelled Mono at the back of the machine, but doesn’t count; nobody wanted to use their Amigas with a black and white TV. So people were faced with a simple choice: either buy the Commodore 1084S or similar RGB monitor with built-in speakers (this cost about 60-70% of the price of the Amiga 500), or purchase the RF adapter add-on which let you use your machine with a TV. The problem was the RF adapter still cost a non-negligible amount of money (about 25% of the price of the monitor) and had terrible image quality. Parents were not exactly thrilled with the prospect of their kids hogging the family TV all day, so most wanted to get their kids a dedicated display. Put it that way, the choice between a proper RGB monitor or a much worse quality small TV and an RF adapter became a no-brainer as the cost was about the same. Another stopgap solution was to use a special RGB to SCART cable with a SCART-equipped small TV, but the results were not as good (the horizontal resolution on a TV is a lot lower, so you could not read 80-column text easily). Plus you could not control your kid’s TV watching habits if they had their own in their room. ↩
-
This is due to the fundamental design differences between Commodore and IBM PC CRT monitors. Commodore monitors such as the 1084S were effectively small high-quality TV sets with RGB input. Commodore was after the home computer and enthusiast market (at least in the beginning), so they found a way to effectively repurpose cheap small TVs into RGB monitors at an affordable price! These small-TVs-turned-monitors had great image quality, much better than your usual small TV, but their resolution and sharpness didn’t come anywhere near specialised IBM PC monitors. PC monitors were the kings of sharpness, optimised for staring at spreadsheets all day at work, but they lacked the qualities of “lesser” CRTs that put pixel art in a more favourable light. Being squarely aimed at the business market, they were several times more expensive than 15 kHz home computer monitors in the 1980s. ↩