Mix3 - Simple black and white channel mixer

by Ferdinand Paris

Mix3 is a simple black and white channel mixer for Bibble 5 and AfterShot Pro. It produces B&W images by mixing the R,G,B channels. It roughly preserves average luminosity (although 'roughly' is the operative term) by taking a weighted average of R,G,B with the slider values as weights.

(Some old-timers will recall that the Andy plugin for Bibble4 had a channel mixer like this, which could be used as a simple B&W channel mixer by turning off the film and paper settings. The replacements for Andy - Andrea & Nostlagia also have such a mixer, but you can't turn off film and paper like you could in Bibble4.)

Mix3 also has its own exposure slider, which means if you happen to mix the channels outside the (0,65535) interval you can use the exposure slider to bring the resulting luminosity back inside the interval without it being clipped. It probably isn't needed given the weighted average calculation, but it's there if you need it.

One possible use of Mix3 is to produce pseudo infra-red images, by boosting red very high and pushing blue very low. If you want to do this you may find that the sliders don't have enough range. You can increase the range by editing the Mix3.ui file. Look for +300 and -300, but make sure that you edit both the slider and the edit box - there should be six instances of each number. The same is true if you think that the range as shipped is too wide. It's hard to know how wide to set the range of each of the four sliders. I've tried to strike a balance, but if you want any of them wider or narrower then it's not hard to edit the Mix3.ui file.

(But note: if you set each of the R,G,B sliders to -100 then the image will go black, as you've set each of the channels to zero. Any other combination of the sliders is ok, but some extreme negative settings can produce odd effects.)

The default position of the plugin is to run late in the processing pipe, just before curves (but before 'Bez - Late' in ASP or 'Bez - RGB' in B5). The 'Early' option runs the plugin before sharpening (and before 'Bez - Early' in ASP or 'Bez - LAB' in B5). Hopefully this should give you enough flexibility to place it either before or after most other plugins. The difference between Mix3 in 'Early' and 'Late' mode is quite noticeable in B5 but negligible in ASP - I'm not sure why this is (maybe it's because in ASP plugins run in linear gamma).

Source Code: When you install the plugin the source code is installed in a 'source' sub-folder for the Mix3 plugin wherever plugins are installed on your system. The B5 version of this plugin uses the 5.0SDK and the ASP version not surprisingly uses the ASP 1.0 SDK. Mix3 is open source.

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Mix3 - Simple black and white channel mixer

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