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I have this image that was taken several years ago with a D70.

enter image description here

It was taken at 1600 ISO which obviously makes it quite noisy. I really want to convert it to black and white, but when I desaturate it in PS it immediately reveals quite terrible banding on the fingers of the guitarist.

enter image description here

Can someone explain why this is, and what I might do to

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The image has some highlights where there is some blue mixed in, where there is otherwise only information in the red and green channels. It's those highlights that doesn't balance well when you desaturate the image.

You can use the Channel Mixer in Monochrome mode to convert the image, that allows you to balance the channels to avoid the posterising.

Example:

enter image description here

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  • \$\begingroup\$ Ahh, Very good! I've never messed with the channel mixer, I'll give it whirl. Thanks! \$\endgroup\$
    – Circle B
    Mar 30, 2015 at 20:34
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    \$\begingroup\$ @CircleB Channel Mixer is an essential tool when doing black and white conversions; not only can you avoid problems like this, but in working with the different blend of colors you can significantly alter the mood of your resulting image. \$\endgroup\$
    – mattdm
    Mar 30, 2015 at 20:54
  • \$\begingroup\$ I can see that! I should've known... \$\endgroup\$
    – Circle B
    Mar 30, 2015 at 21:11
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    \$\begingroup\$ It is like using color filters back in the days of B&W film. You can cut the tonal value of some colors while keeping the full value of other colors. \$\endgroup\$
    – Michael C
    Mar 31, 2015 at 2:06

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