Now back to the Layer Palette. Select the Background layer and press Ctrl+J. It will duplicate the background layer into new layer. We will be using this new layer for layer blending to enchance the contrast of our black and white image.
Now select the 'Multiply' Mode for the new layer as shown above, and adjust the Opacity until you think the black and white look good. Note that you might find when part of the image look good, another part of the image might look too dark or light. We can solve this problem by using layer mask.
First adjust the image with Opacity until you see most part of the image look good. Then apply the layer mask by click on 'Add Layer Mask' button, with the layer mask we can tell photoshop how much 'Multiply' blending effect we want to apply on which part of the image. Press B to access the Brush Tool, paint Black to totally remove the effect of 'Multiply' and paint white to totally apply the effect of 'Multiply', while painting any value in between black and white also allow you to control how much 'Multiply' Effect should apply on which part. See the final result on the right. I painted the foreground leaf and the valve with full black to remove the multiply effect where I found it is too dark, and I painted the simen and the background leaf that near the simen with 50% gray.
First convert the image to Lab Color mode by selecting menu 'Image'->'Mode'->'Lab Color'. We want to extract the Lightness channel of Lab Color into independant grayscale image. Go to Channel Palette and select Lightness channel.
Now go back to menu 'Image'->'Mode'->'Grayscale', click OK when ask if you want to discard the other channels.
In this tutorial we will be creating black and white image with the Lab Color mode, and the selectively add layer mask on the layer blending so that we can chose which part to be lighter and darker. Because black and white image consist only black, white and the grayscale value between these two colors, all we can do to distinguish foreground object from background is its lightness value.
We will be using the image on the left to do our tutorial. Download the project file here.