Could be editor's monitor or artist's graphics creation as it needs to be high resolution and drives the Apple monitor or Mac third-party compatible monitors. Is the connector 15 pin? Then that is for Macs with nubus bus slots. Mac II, Mac IIfx, Mac CX, Mac ci etc.

Could not find any details on Sigma Designs 53C328 chips.

Cheers,

Sadly sigma has never had a comprehensive list of devices made, everyone knows who they are but no one has bothered to make an archive of the things

…
Sigma Designs pitched monitors at both the Mac II and SE as well:
Sigma Designs will exhibit its LaserView Display System, the highest resolution (1664 x 1200) monitor and display board system available in non-interlaced mode for Desktop Publishing and Engineering. LaserView monitors come as 15″ or 19″ landscape models and provide useful features such as dual resolutions, multiple cursor sizes, switching between screens, screen-save timer, and others. The LaserView Display System works with both Macintosh SE and Macintosh II.

24bit color = 8 bits per channel, R+B+G.. though the apparent 1Mbyte for each channel don't sound like much at 1 byte per color pixel, unless it's only a line buffer not a frame buffer.

Interesting. just got off work and cannot help much but here are the Sigma websites: www.sdesigns.com/ before changing to www.sigmadesigns.com
http://web.archive.org/web/19961219175311/htt … w.sdesigns.com/
Unfortunately most of their old stuff was on ftp. Is all I have on quick look, I do have an old ISA Sigma VGA card but never found anything about it either...

BitWrangler wrote on 2022-10-14, 04:16:

24bit color = 8 bits per channel, R+B+G.. though the apparent 1Mbyte for each channel don't sound like much at 1 byte per color pixel, unless it's only a line buffer not a frame buffer.

Yea I get that, but those are 3 triple 8-bit DACs, so 3x 3x 8-bits, which would be 72bits in total. That seems a bit weird to me.
Also the amount of memory surely doesn't seem like much at first, but considering the time this card came out, most of the cards went with a lot less.
I have a very high end IBM PS/2 XGA card of roughly the same vintage that comes with 1MB, half of which is an optional add-on board which is as long as the card itself 😁

From what I can find in old magazines like macworld, there used to be several products like Silverview, Pageview, Laserview and Colormax.
I'd rule out the Laserview from the start since the ISA version looks significantly different than mine. Only has one large Chip compared to the 6 big QFPs on mine.
https://www.ebay.com/itm/334581088342?hash=it … =p2047675.l2557

My best guess would be the ColorMAX, since it also kind of fits best to the "CMA-M2-0024" model-number.
https://archive.org/details/MacWorld_8901_Jan … /2up?q=colormax
Can't be sure though...
Also very weird, the prices range all the way from roughly 1500 to over 6000$ I guess card and monitor. Most were around 5000$ in magazines from '89.
I guess thats why there is not many of them around...

Well anyways, since I have no means to test it, at least I had some fun digging in magazines for information about it 😀
I did put it on ebay for auction now if anyone is interested in playing around with it.