Bit depth and Hue/Saturation

[dror_guy]

<p>I'm quite new in this and don't fully understand... I'd be grateful for help....<br>

When I take a photo from my understanding (which might be wrong)... Say I have a 12 bit depth camera... I understand that each RGB channel has 4096 values of LUMINOSITY.<br>

If that is true - then where do the hue and saturation come from in the raw file?<br>

Also, the color gamut palette which I see in wikipedia - does it describe different combinations hues or saturation or luminosity? (I guess it's not luminosity because I don't see any black there...)<br>

Thanks, <br>

Dror</p>

[howard_m]

<p>http://en.wikipedia.org/wiki/HSL_and_HSV</p>

[digitaldog]

<p>Color Gamut and bit depth have nothing to do with each other. Further, bit depth is just a mathematical construct of dividing up colors. That doesn't mean we have that many colors and further, we human's can't see anything close to 16.7 million colors let alone billions. </p>

<p>Think of this like a staircase. The length is gamut and let's say our staircase is 20 feet. We have 20 steps, one foot apart, that's our bit depth. We have another staircase that is also 20 feet (same gamut) but the steps are ½ foot apart. Twice as many bits, but the staircase and thus gamut is the same. More bits isn't more gamut. </p>

<p>When you view a 3D gamut map, luminosity runs top to bottom (Lstar if you view that way). Hue and saturation run the other two axis. Kind of hard to describe with words. And really hard to describe with a 2D gamut map. </p>

[Wouter Willemse]

<blockquote>

<p>Twice as many bits, but the staircase and thus gamut is the same. More bits isn't more gamut.</p>

</blockquote>

<p>Exactly. I think the confusion is coming when you start to (heavily) edit the picture. Try to make the 20 feet staircase look like a 40-feet one, and you will have resp. 2 and 1 feet steps. The point is, you cannot add steps (bits) after the fact - so whatever steps you have, have to cover the distance of the stairs. And while 1 feet steps may still make for an elegant undisturbed gradation, 2 feet steps become visibly blocked (banding, more usually called <a href="http://en.wikipedia.org/wiki/Posterization">posterization</a>).</p>

[dror_guy]

<p>Ok, thanks everyone! :-)<br>

I think I now understand where my confusion was... I thought that hue and saturation is an additional data information to the RGB data. But RGB and HSL are the same thing but on different scales and can be derived from one another...<br>

So if I'm now right - camera raw gives us the pixel image data in RGB channels (the bit depth indicates the number of bits available on each channel). Then in Lightroom and Photoshop or any other image editing software we can brighten and darken these pixel RGB channels, but we can do it in different ways and on different scales (such as hue and saturation).<br>

I also found this link with matematical conversions:<br>

http://codeitdown.com/hsl-hsb-hsv-color/<br>

Please let me know if I got it right this time.<br>

Thanks again,<br>

Dror</p>

[digitaldog]

<blockquote>

<p>So if I'm now right - camera raw gives us the pixel image data in RGB channels...</p>

</blockquote>

<p>Kind of <g>. The raw data is more akin to a grayscale file but after demosaicing it becomes an RGB three channel document. <br>

<img src="http://www.digitaldog.net/files/raw.jpg" alt="" /></p>