Re: [GM-core] ChannelThresholdImage interface

At 12:41 AM 3/20/03 -0600, you wrote:
>ChannelThresholdImage is considerably faster due to the latest code
>updates (in CVS).
>
>Unfortunately, I don't like the functionality of this routine very
>much.  The thresholding is specified like 'threshold' (e.g. "30%"), or
>'red/green/blue/opacity' (e.g. "30%/40%/50%/60%").  The problem with
>this interface is that *all* channels must be thresholded.  It would
>be nice if the user could specify channels to ignore so that only one
>or two channels could be thresholded.
>
>Does anyone have an idea of how the current syntax can be supported
>while also being able to specify that a channel should not be altered?

Two possibilities:  Use negative input for channels to be ignored,
or define another input option -channel-select <mask>.  I think the
original intent in ImageMagick was to do the latter, but it has not
happened yet.  Channel selection is a little confusing because we need
to consider CMYKA, in which the opacity channel is displaced into
the index channel.

Glenn


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