h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Actually, true colour is really 24-bit, having 0-255 (or 0-FF) red, green and blue values. When it's quoted 32-bit, what they *really* mean is that they're going to leave an 8-bit space next to ever 24-bit colour code, making everything fit into memory much neater, hence speeding things up.

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In some circumstances this 'spare' 8 bits can be used to indicate transparency. (Useful when combining images.) This is often referred to as the 'alpha channel'.

About a dozen years ago, Targa produced real 32-bit colour. I know, I was writing code to manipulate them. I know all the bits weren't used, but to delve into that would be to kick this entry cleanly out of the reach of the lay reader who wants to know how the web palette works.

I apologise for elisions that might be taken as falsehoods. You gotta admit that colour is a gnarly thing to put in words.

The first two sentences of my previous post are unclear -- I was thinking faster than I was typing. I was referring to Targa boards, whose output I was writing code for.

Them were the days.

Grin, sorry, forgot to put my customary 'Nice article ' at the end of my equally customary uselessly pedantic post...

If you're talking about standard windows screen modes, though, AFAIK 32-bit always means 24-bit with a gap. Some scanners, I think, boast 30-bit (three sets of 10-bit) colour, but personally I'm dubious as to whether the human eye can actually see that many colours...

Nice article

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The fellow I worked under when I first worked in image software was quite convinced that humans can't distinguish more than 256 colours on the screen except for continuous gradients -- but then, HE was colourblind, too!

Thanks

Doesn't some digital post production work in film use 48 bits per pixel? Whilst 24 bits is more than the human eye can discern in any single image, this ignores the fact that we can accommodate a much wider range of brightness thanks to our irises.

On film, the brightness level that can be displayed is pretty wide - outdoor scenes in bright sunlight can be much brighter than indoor scenes, and nighttime scenes. (On TV there tends to be less range - outdoor scenes will be darker and indoor scenes brighter than they would be on film.) Our eyes will 'stop' up or down accordingly. For any one brightness level 24 bits is sufficient, but to be able to represent both bright and dark scenes, you turn out to need more.

I can only answer as a digital painter, i.e., from the right brain. It sounds right what you say, but in painting terms it's because the light (or the darkness) eliminates so much of the midtone range that provides texture and modelling to an image and leaves you with aforementioned continuous gradients, which is why pictures with sky in them were always a pig to paint digitally in the early days.

Even with what seems like an insanely limited number of colours (256), you could get away with a lot of expression if you studied Seurat and worked at the pixel level. I think I have a couple of images from that era, which I could put up at my gallery for a few days, if you are interested to see how digital painting methods have changed. I saved one in particular, an illustration from a fairy tale written by a friend, because I remain pleased with it as a technical exercise.

I'd certainly be interested. My background is more technical - I've worked on layout and drawing programs, and I've also done a lot of work on digital video systems, as well as always having had an interest in computer graphics.

Never much of an artist though. (Music has always been my expressive outlet, rather than anything visual.)

Tomorrow I'll sneakerware the image off my desktop system and onto this my notebook, and from there to da gallery. I'll post the URL here.

Fudging; 30-bit colour scanners

The point for 30-bit is that, before finally scanning, you do a preview, and fiddle with brightness and contrast virtual knobs etc. So consider a dark picture, for example; more bits mean that you can extract a clearer scan of it. Or something like that.

I've posted an Old Digital art sample at:
http://www.h2g2.com/A378740

for anyone who wants to see how titchy it used to be.

Now that was a trip down memory lane! More comments on your page. Thanks for doing that!