Here's a quick step-by-step plan for using Channel Mixer to convert your RGB image into grayscale. This method doesn't take full advantage of the potential of a RAW file. But for some images this method is quite adequate and it is relatively fast.
1) Open your RAW file in Camera Raw.
2) In Camera Raw, set Exposure controls to optimize your color image. Don't desaturate. It's best to work in Adobe RGB, 16 Bits/Channel, which gives you a wide color gamut. The more colors you have, the more effective Channel Mixer will be later.
3) Open the RGB file in Photoshop.
4) Select Image > Adjustments > Channel Mixer from the main menu, or select Channel Mixer as an adjustment layer, in which case a layer mask can give near infinite local control. Figure 1
5) In Channel Mixer, check the Monochrome box. Figure 2
6) Adjust the Red, Green, and Blue sliders to obtain the desired effect
1) Open your RAW file in Camera Raw.
2) In Camera Raw, set Exposure controls to optimize your color image. Don't desaturate. It's best to work in Adobe RGB, 16 Bits/Channel, which gives you a wide color gamut. The more colors you have, the more effective Channel Mixer will be later.
3) Open the RGB file in Photoshop.
4) Select Image > Adjustments > Channel Mixer from the main menu, or select Channel Mixer as an adjustment layer, in which case a layer mask can give near infinite local control. Figure 1
Figure 1
5) In Channel Mixer, check the Monochrome box. Figure 2
Figure 2
6) Adjust the Red, Green, and Blue sliders to obtain the desired effect