On 3/27/23 15:28, Alain Martel wrote:
> Remember that 8 bits and less are paletted formats and that 16 or more 
> are non-paletted.

This doesn't look to me to be strictly true. It might be 'typically 
true' for height_field images in some formats with respect to 
traditional POV-Ray usage.

> IIRC, in hight fields, when the image is 24 bits, the red and green 
> channels are used to to represent the high (green) and low (red) bytes 
> of a 16 bits value and the blue channel is ignored.

In official POV-Ray releases: "when the color image is <=8 bits per RGB 
channel"

And, I too flipped the importance of green and red in one of my earlier 
descriptions - probably because green in typical color to gray 
conversions matters most to luminosity / the gray level.

It's not how the special (<=8 bit a channel) color to gray conversion in 
POV-Ray works where the most weight is in fact given to red.

> 16 bits is often called high colour and 24 and 32 bit are called true 
> colour.

Ah yes! I remember being so excited to finally be working on a true 
color display! :-)

My college terminals were teletypes.

I started work years on green and black IBM 3277s - and white and black, 
vector displays, I think, IBM 2250s or 3250s. Those latter displays had 
light pens you'd bang directly on a heavy glass screen for selection and 
movement.

Once you got a lot of vectors up, the refresh rolled across the screen 
at a few screen refreshes a second - and selection and movement got 
really hard. The heat on our faces and the sound in the terminal rooms 
was something else when folks were really cranking.

There were some black and green Tektronix displays in use too for our 
graphics. They were nice because they didn't flicker at high densities. 
The image was written on a screen sort of like an etch and sketch - 
until you refreshed. I cannot, at the moment, remember the models.

My time on another planet...

Bill P.

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