[Digikam-users] canon eos20d and unsharp mask

[Dik Takken]

On Tue, 30 Jan 2007, Andrew Atrens wrote:

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> Hi folks,
>
> I'm processing raw images captured with my EOS20D ..
>
> Canon puts out a quick reference guide for 'tips and tricks for
> maximum image quality' in which they advise -
>
> "Canon EOS digital cameras have an anti-aliasing filter installed on
> the image sensor.  This filter improves color rendition and
> practically eliminates moire. The liability  is a slight reduction of
> sharpness. To reduce the softening effect of the anti-aliasing filter
> we recommend applying an unsharp mask to the image in Adobe Photoshop.
> Although there is no such thing as a 'best' setting for all
> applications, we suggest the following as a starting point"
>
> Amount: 300%
> Radius: 0.3 pixels
> Threshold: 0 pixels

These settings sound like they would be far too strong for my taste. 
Unsharp masking this strong may greatly amplify sensor noise also...

I would immediately turn off the anti-alias filter, as you can probably do 
things better in software. Also, anything the camera does for you, you 
cannot undo later on.

> I'm noticing that the digikam unsharp mask plugin has a minimum
> 'radius' of 1 pixel. Which seems more intuitive than '0.3' pixels.

A radius of < 1 pixel does make sense actually, you can use it when a 
setting of 1 pixel is not good enough. Try the GIMP, it can do unsharp 
masking < 1 pixel. Maybe Krita can do this as well. I guess it would be a 
good idea to submit a wish for DigiKam to support this as well.

> And secondly, can someone recommend some general guidelines for using
> unsharp mask? - Unless I ask the camera to do the sharpening
> 'in-camera' using 'Parameters' settings, I think I'll need to apply
> this to every raw photo I take. After staring at a photo for a while,
> one begins to second guess one's instincts about what settings 'work
> well' and which ones don't.

It's all a matter of taste, really. Unsharp masking is not always the best 
option, though. Do a search on internet on 'smart unsharp masking' to 
learn how to do it properly.

Dik