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We are now going to look at the Grayscale Color Mode which we access from under the Image menu, Mode > Grayscale. Now let me just say that if you're converting a color image to grayscale, this is not the best way to do it. The best way to do it to my mind would be actually to retain the image as an RGB image and just apply a black-and-white adjustment layer to it so that it has the appearance of a grayscale image or a black-and-white image. And then you can mix the different colors that go into the grayscale to adjust the contrast of the image.
That way you always have the option of going back to the original color image should you choose to do so, and you can introduce some interesting color tints into the image by clicking on the Tint checkbox. But I'm not going to do it that way; I'm going to do it by actually converting it to an official grayscale image which -- it's going to mean that we have a single channel in our resulting image. We get this warning message here, suggesting to do what I just did is to use a Black & White adjustment layer, but I'm going to ignore this advice and click Discard so that I now have a single channel image and so that my image is now 1/3rd the size of its former file size.
So as a Grayscale image we have a direct path to the Bitmap color mode which is going to put all that pixels to pure black or pure white, you might use this for line art or you might rarely use this to create some sort of special effect. More interestingly we have the Duotone color space, where we get the advantage of retaining our image as a single channel image which is very economical in terms of its file size but printing it in two, three, or four inks - Duotone, Tritone, or Quadtone.
I'm going to use one of the presets to start with, we have got a number of presets to work with and then we have a duotone made up of Black and PANTONE 485. We have two ink colors but we still only have one channel. We can affect the amount of ink by clicking on the curve, and these curves operate in a similar but slightly different way to the curves that you are used to from the Curves adjustment layer or the Curves adjustment. Rather than pull them around you specify numerically how much of the color you want at any point in the scale.
So at the moment the 50% point is right there, there is only 15% of the red at the 50% point which is why the curve is much reduced and it's the shape that it is. I'm going to increase that to 25% and we should see that the image gets a little bit redder as a result, and then at the 100% mark I'm going to say I want 75% red and that makes a little redder still. So I could now go ahead and print my image like this and it's going to print in two inks or perhaps I want to add a third ink as well as choosing the presets you can just click on a color swatch.
I'll need to convert that to a Tritone if I want to add a color. Click on that Color Swatch and you can add any color that you like as the third color ink and you can come in and affect the amount of that color by working on its curve. I'm going to reduce the amount of that color of the 50% mark to about 40% and 100% will take down to about 80. So the yellow is not quite as strong as it once was, but we now have an interesting sort of sepia effect applied to this image.
Now you may be thinking that's an awful lot work to get a sepia effect and I would agree with you, and if all you want is the sepia effect then you might as well retain your image as an RGB image and apply some color effect to it, while it's still an RGB image. The reason duotones were used and they were used more frequently than they are today is that they are an economical way of working with a limited color palette. Today because of digital printing it doesn't cost much more to print in full color than it does to print in two or three colors, so the economic imperative to use Duotones, Tritones or Quadtones is no longer there in the same way as it was back in the 1990s.
But if you like the effect of duotones by all means you can get to them like this, should you make a duotone you will need to retain it in the Photoshop file format, don't save as a TIFF and you cannot save it as a JPEG. I'll be talking more about duotones in the chapter on working with a limited color palette.
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