My impression is, that there is rarely another chapter in the PDF standard which causes more confusion than the one about output intents. The standard allows for specifing output intents for any output device that can be a target of a PDF rendering process. However, in my opinion the output intent is primarily a means to describe the characteristics of a printing device. And, I think that its use should be limited to this purpose. But why? And, what's the impact on practical applications?
An output intent only has an effect if device specific color spaces such as DeviceCMYK and DeviceGray are explicitely or implicitely used in a PDF document which matches the color space of the output intent's ICC profile. This means, that if there aren't used any device specific colors in the PDF document then the output intent is obsolete. The output intent has two functions. First, it is a convenient way to associate device specific colors with an ICC profile, and second, assigns that same profile to the intended target output device. The color profile must be able to map colors from the profile connection space (PCS) to the output color space and vice versa.
Theoretically, the above is true for DeviceRGB output devices. However, I wouldn't recommend to use it in an output intent for the following reasons:
- If a document contents of a PDF document contains both DeviceRGB and DeviceCMYK color spaces an output intent for the DeviceCMYK color space is preferred in practical appliations.
- DeviceRGB color spaces can easily be replaced by CalRGB color spaces that don't need an output intent.
- If two documents are merged it is much more convenient if they have the same color space in the output intent.
Does this sound reasonable to you? Do you know other reasons why to use CMYK output intents only? Or, do you disagree with my recommendation? Please, let me know and post a comment.
