1) - To get a monochrome IR effect starting from a colour image, first adjust as usual to get lightness and tone range to your liking. Don’t worry about colour balance.
2) - Bring up the channel mixer (under Image > Adjust). Tick the box for ‘monochrome’ so you can see the effect of adjustments. Increase red and green sliders and reduce blue. Figures suggested by Mel Giggs at a previous DI meeting are:-
Red - 178%; Green - 82%; Blue - minus 142%
I use a bit less than this. As long as red is increased and blue is reduced you will get the effect of IR or a strong red filter. When satisfied, click OK and then readjust levels to obtain an acceptable picture.
3) - IR pictures tend to have the highlights spreading into the rest of the picture. A way of adding this effect is to make a duplicate layer, lighten this by adjusting the central slider in levels and then blurring this layer (Gaussian blur under filters). Reduce the opacity of this layer to blend with the original. This can also give an interesting ‘IR’ effect using a normal monochrome original.
4) - If desired, a ‘painterly’ feel can be introduced by adding edge effects. Make another duplicate layer of the non-blurred IR image and use the find edges filter (under stylise). Reduce the opacity to blend with the original and the blurred layers. Don’t overdo this effect - a suggestion of an ‘edge’ is better than a hard outline around every object.
5) - When happy with the result, save the image with all layers as a Photoshop file (you may change your mind and want to make alterations).
6) - As a further refinement, I sometimes add some ‘grain’ using the noise filter (monochrome noise for a monochrome picture!). This is also possible using film grain under the artistic set of filters.
7) - A method of finishing the picture is to use a vignette. My method is to make a rectangular selection very close to the edge of the frame. Feather this by e.g., 100 pixels and invert the selection. Increase brightness and decrease contrast and repeat twice more to produce the vignette. A thin black line around the whole makes a good final border (with black as the background colour and the selection removed, increase the canvas size by an appropriate amount).
8) - Steps 3) to 7) can also be used to make colour images with the feel of a pastel drawing. When making these I usually adjust levels by moving central slider to the L and the left slider to the right to give a lighter print still retaining some dark line detail. Colour saturation is reduced (image > adjust > hue and saturation) and the image is printed on a good quality uncoated watercolour paper.
9) – Don’t forget to use adjustment layers where you can so as to preserve image quality.