How necessary is accurate masking while editing an image?

Question

I'm editing an image of a bronze statue of a horse and rider shot against the sky. The image is excessively blue of course and I want to mask out the statue so I can edit this spearately from the sky. It was shot in RAW on a Canon 450D.

As I'm creating the mask and I zoom in more, I notice I've left sky pixels behind. There also some purple fringing I'm noting at 100%, becoming quite clear at 200%. Understandably, I don't really want to zoom into something ridiculous to remove individual pixels.

How large a print would I have to make in order for the remaining blue pixels to be noticable? Bigger than A3 for example? Is there some way I can assess what the impact of those remaining pixels or the fringing will be, if there will be one at all?

Answer

If you want good results accurate making is essential. While you are unlikely to see the fringing itself on a print you can end up with the masked object looking like a cutout. This effect can be eliminated by going round the edge of the objects mask with a soft low opacity brush in order the feather the edges of the mask. This will eliminate the odd bright sky pixels that you see around the edge of your statue and should eliminate the fringing.

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