>> Dear Richard,

This is mentioned in the photoshop bible and other books I think.

The blue channel is generally considered to be noisiest channel on chips,
whether scanning or on camera.

In channels, select the blue one if that is the noiseiest. Then go to
filter/blur/smart blur. Then choose the quality high option. Then use smart
blur and see how much to apply, the default is normally quite close. <<

Ian, I always disagree with this common  knee-jerk response.

My advice is to indirectly attack the problem, rather than directly.

I agree that the B channel can often be bad, even more so if an image has
been through lossy compression.

But one can do better than directly filtering the blue channel.

Using a duped layer or the fade option after the filtering, use the COLOR
blend. This will blur the hue/saturation portion of the image data while not
blurring the detail.

I like a duped layer or a merged visible layer for this exercise, set to
color blend mode.

One can use many filtering methods to average or blur or whatever. The smart
blur is a good choice, as it can preserve edge detail.

The beauty of this method is that it can correct issues in the red channel
too, usually the green is not better off but it can be depending on content.
It depends on the image on whether the blue or any other channel is better
or worse than the others, but as a general rule the G is best, with R next
and B last.

One can apply this layer to the underlying layer in many ways...then flatten
down (or not).

Then, one can directly attack the blue channel if there are remaining
issues. My suggestion is to go for the colour blend first, before directly
blurring the blue channel. The colour blend can actually restore the
appearance of valuable detail instead of simply blurring whatever detail and
noise is currently there.

Please try it, I think you will find that this provides better results.


Regards,

Stephen Marsh.

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