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Question about image bit-depth and CPU bit-power

Old 05-17-02, 04:40 AM
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Question about image bit-depth and CPU bit-power

I was at a training course for work yesterday and we were told that the new Sony Digital Still cameras capture at 14-bit DXP (Digital Extended Processing) and that all other top range ones only do it at 12-bit. Then he went on to say that all computers process at 8-bit so the 14-bit image the camera captures will be downsampled anyway.

I don't get it??
As far as I know computers these days process at 16, 32 or 64-bit depending on CPU and OS, and the only difference that makes is speed and efficiency when doing tasks. The colour depth of an image has nothing to do with that. Even if I set my screen colours to 16-bit I can still process a 24-bit BMP file. Even if I can't see the extra colours on screen.

I know I'm missing something.
What was this guy talking about?
Old 05-17-02, 08:01 AM
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Well, first off, the image depth (typically 8-bit, 24 million colors) is completely independent of the bus architecure used. They have absolutely nothing to do with each other.

Now, on to the next part. I admit, I haven't heard of Sony's cameras using a 14-bit CCD; I haven't heard of anybody using a 12-bit one, either. To the best of my knowledge, all use 8-bit, 24m color CCDs. The advantage to a 12- or 14-bit one would be more colors (probably in the shadow or highlight detail areas).

If, indeed Sony had a 14-bit sensor (or a 12-bit one, for that matter) I think I would be swayed to buy a digital camera that much sooner!

PhotoShop can work with 8-bit images or 16-bit images (with limited functionality), so saying that all computers work in 8-bit only is simply wrong.
Old 05-17-02, 02:11 PM
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Just thought I'd clarify some points.

As danw stated, the pixel depth of a frame buffer has very little to do with the CPU or memory bus widths. The confusion here has mainly to do with color processing and color display.

The display on most PC devices is limited to 24 bit color. That's 8 bits per channel, RGB. Since the video card hardware is typically designed around this standard, any image that gets displayed to the screen must necessarily be conformed to that standard. (BTW, ticky tack correction, 8 bits per channel=16.7M colors)

However, that's not to say that images can't be acquired, processed and stored in other formats. Scanners, cameras, any digitizing device basically, benefit from a design that uses more bits for image acquisition and processing. Digitizing at higher bit depths amounts to oversampling and any processing that can be done with the higher bit depths minimize quanitization errors.

BTW, a couple little odd facts. The 32 bit color depth available on many PC video cards doesn't actually offer more color information. It's still 24 bit color, but they just add 8 bits for an alpha channel. Also, the bit depth per pixel doesn't have to be symmetrical. They sometimes allocate more bits for the green (usually) channel.

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