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Author Topic: Errors in Understanding Bit Depth tutorial  (Read 2880 times)


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Errors in Understanding Bit Depth tutorial
« on: August 20, 2007, 01:43:34 pm »

I love this site and I've learned a lot about photography from it - thanks Michael Reichmann!

This tutorial on bit depth contains a number of errors:

>This is why you don't want (for example) to print a B&W image on an inkjet printer using just black ink. The printer would only be able to lay down 256 shades of gray, from black to white — not nearly enough for a decent image. Instead you should print using colour inks as well, which means that all three primary colours (Red, Blue and Green) will be mixed together to create 16 million shades of gray (256X256X256). More than enough.

This isn't true at all.  While 3-channel color inks using 8 bits per channel can indeed render 16 million different colors, most of those will not be anywhere close to gray.  Only 256 will really be gray.  But I wonder, unless you're going for a duotone or tritone look (see: ), is it really better to not use black ink to make B&W prints for some reason?  I suppose you might be able to get a few more gray levels if you mix black ink and colors - certainly not millions, but possibly up to twice as many.  Do any printers even do this?  I would be surprised.  And are 256 levels of gray for printing *really* not enough for a decent image?

>A 48 bit image is capable of billions of colours.

If anyone is confused, yes, it really is roughly 300 trillion colors.  A nitpick, certainly, but confusing if you're trying to understand how this works.

I appreciate the rest of the article, which explains how higher bit depth allows aggressive use of tools like curves and levels without causing as much posterization.
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