What is the difference between 24bit & 32bit?

[Picard]

Hi Friends,

Would you please inform me what is the difference between 24bit & 32bit color mode? Honestly, I can not see the difference in image quality for both mode. Does any of you can spot the difference? Your advice and information are very much appreciated. Thanks.

Regards, Picard.

[Kruzin]

24bit is ONLY for 2D. It is not H/W accelerated.

For 3d, you must use 16 or 32 bit.

The extra 8 bits go to transparencys, stencil buffers, alpha channels, and whatever else....

[This message has been edited by Kruzin (edited 28 November 1999).]

[Picard]

Kruzin, thanks alot for your info.
For 2D, when 'transparencies', 'stencil buffers', 'alpha channels', etc. are not applicable, is there any difference between 24bit and 32bit?

In 2D condition, can you spot any image quality difference between 24bit and 32bit? If I'm not not wrong, we can see a strong image quality difference between 16bit and 24bit in 2D mode.

Kruzin, thanks in advance for your nice response.

Regards, Picard.

[Kruzin]

In 2D, you should see no difference between 24 and 32 bit at all...but there is a big difference between 16 bit and 24/32bit on your desktop...

[Maggi]

Hi Picard,

even for 2D (Photoshop for example) I've set my desktop to 32bpp, because then I can use the the extra 8bit to generate masks (alpha/transparency channel) hardware assisted ...





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Cheerio,
Maggi

Home rig:
Celeron333A @ 500MHz
Asus P2B-S @ 100MHz FSB
2x 128MB CAS2 SDRAM
Matrox G400 @ 150/200MHz core/mem clock
... and some other goodies ...

[Picard]

Hi Maggi,

Thanks alot for your information. I use Photoshop too. So I'll try your recommendation. Btw, beside for hardware assisted process, if we just use for 2D image viewing (ex: view an image using ACDSee), does 24bit and 32bit make a difference, or not at all?

Thanks again for your nice response.

Regards,
Picard.

[gbm]

The difference is in speed only, which is maybe not so important for static image viewing.

[Gurm]

Another difference which sometimes gets left out of these 24/32 discussions is that in 32-bit mode, all the data is aligned differently than in 24-bit mode. This CAN depend on the specific implementation - i.e. how Matrox did it instead of nVidia. But odds are 32 bit will ALWAYS be faster, simply because it can be done as one 32-bit read, or two 16-bit writes, or whatever.

- Ash

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Listen up, you primitive screwheads! See this? This is my BOOMSTICK! Etc. etc.

[Maggi]

yep, Greg (GBM) is right ...

Do some 2D benchmarking to get a readout of the difference and Post 'em.


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Cheers,
Maggi
________________________

Working Rig:
Asus P2B-DS @ 103MHz FSB
Double Pentium III-450 @ 464 MHz
4 x 128MB CAS2 SDRAM
Matrox Millennium G400 32MB DualHead
Nokia 445Xi (21")
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Home Rig:
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CTX VL710T (17")

[KvHagedorn]

There hasn't been an excuse to leave 32 bit mode since the Millennium I came out, as far as I'm concerned.

I remember in ancient times (about 10 years ago) when one could buy a $2000 full length accelerated (2D) color card which could render a full screen 24-bit image in only ~10 seconds! (wow) The thing weighed about a ton and was chock full of RAM (4MB was a huge amount, 8MB was awesome.. about an extra thousand $$$).

24 bit color was the absolute pinnacle then, and most people couldn't afford it, or use it for everyday tasks. Now look what you get for 1/10 the price (and weight).. 8x the RAM, about 20x the speed, and in 32 bit color! With 3D acceleration! Geez, we are spoiled now



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Kind Regards,

KvH

[bobby2]

Arghhhhh
for 2D:
24 bit mode offers 16 million colours
32 bit mode offers 4 billion colours
OR
24 bit mode offers 256 colours for Red,
256 for Green and 256 for Blue
32 bit mode offers 2048 for Red, 2048 for
Green and 1024 for Blue.

For nearly all purposes 24 bit is fine. But if an image has a large degree of colour gradation in it, then it wont be good enough. Imagine (think Kodak Adverts in UK recently) a Red Setter dog in an autumn wood of red leaves with a beautiful red sunset in the background ... lots of Red!

32 bit is obviously far better for these purposes. Havent any of you ever wondered why good scanners are 12 bit per channel or better and not 8 - 16 bit per channel is 65536 colours for each of RGB - some scanners allow this, and Photoshop will let you muck about with images of this kind for a reason!

Lesson ends (ive just finished teaching a class on this

[AlgoRhythm]

Sorry, bobby2.

You're a bit off on this one.
On a video card, 32 bit is only 24 bit aligned on 32 bit boundaries for faster access.

Yes, on a scanner that's correct, but not on a display.

AlgoRhythm

[gbm]

Bobby2,

I think you should give big apologies to your students, cause you gave them a big piece of misinformation.
AFAIK, there are only a few models of high end SGI machines (not ordinary workstations) providing more than 8 bits per primary. Mainly because more than that is not needed outside of very professional (movie production) world.

24 bits give over 16 million colours. The human eye is capable of recogniziong about 10 million colours. Unfortunately these 16 mln do not cover the 10 mln fully, so 10 bits per primary are good, especially in shades of grey (but for red 8 bits suffice). But then - nobody cares of these subtle shades, so the whole industry stays at 8 bits, which is enough.

[bobby2]

Let me go over this again.

Some images will require more colour in one particular shade. E.g. my very RED example. If I scan this image with only 8 bit depth on the red channel then it will not be captured completely (i.e. info will be lost).

The human eye works on an analogue system where luminance and chrominance (brightness/ colour) are seperated in such a way that we can 'pick' 10-16 million colours (less after getting to about 12 years old - a truly dissapointing fact of life - sound is like that too). We see a scene and our brain can percieve nearly 10+ million 'shades' - for want of a better term - as these arent actually colours in the RGB sense. If we look at a very RED scene then we might see 10 million 'shades' of red. Our amazing brain does the work of shifting what our eyes see into our own ever deteriorating colourspace.

'AlgoRhythms' point is valid - most displays work in 32 bit better due the internals of machine architecture (4 byte word systems, or 32 bit), better due to speed. But then ...

Display systems using 8 bits will approximate these colours using what they have available. If the image is scanned in 12 bits then we get dithering (a very nice dithering) down to 8 bit. But the dithering makes is faking it.

As for 'gbm' Anyone who has tried printing a lovely onscreen image will realise that your display is not the same as the ink, is not the same as your mates display or her printer ink etc.

Ive gone over this one for 'gbm' because my students were NOT misinformed at all. The 'head in sand' quote 'nobody cares of these subtle shades' is akin to the old SVGA days when I remember people saying '256' is enough - except for professionals. Your argument that 8 bits per primary is enough is as holed as a sieve - why not 6, or 10, or 12. If I have more then I can be more sure that Im seeing something closer to what I would in real life. That 10 bits of colour for my very RED image is not enough - 1024 values.

Ask ANY archival photographer, or NASA with their onboard cameras - they (and I) store images at as high a depth as possible - 48 bit (16 bits per RGB) is about the top end now. The difference in quality of a 48 or 36 bit scan over a 24 bit one is instantly obvious because a real life image isnt seen in RGB.

Of course, comparing a 24 bit scan next to a 36 bit one on a monitor working in 32 bit (24 bit underneath the 32 bit alignment) will be more or less pointless - but printing these onto a professional piece of kit will show considerable differences.

The printers we have on our desktops now are the professional printers of 5 years ago - and I should hope that the 'high end' SGI display we have now will be on our desktops sometime in the future.

bert
excuse the big rant - but I like a nice discussion