How to select a CMYK color channel, rasterize as grey scale and halftone into new pixel layer

[issicus]

I know how to do this in photoshop but I'm having a hell of a time figuring it out...  Someone want to walk me through it?

steps in photoshop

Open CMYK file.  
Select a color channel (ex; magenta)
Change mode to grey scale and discard not visible color channels
Change mode to bitmap select halftone
Change mode back to grey scale and magic wand the halftone out
copy and paste halftone into document 

[NotMyFault]

I have no access to PS, so interpreting your edit steps and might be wrong

8 hours ago, issicus said:

Change mode back to grey scale and magic wand the halftone out
copy and paste halftone into document 

• add a channel mixer adjustment layer on top of you source layer
• Choose C channel
• set C input to 0, magenta to 100
• repeat for Y and K channel
• Now you have a view showing magenta on all color channels (greyscale from magenta)
• Add a halftone live filter (this is available only in Affinity Photo), but you can open a file containing that filter and copy/paste it into your file
• Adjust halftone settings as needed
• merge visible

dont now who to interpret the last steps

8 hours ago, issicus said:

Change mode back to grey scale and magic wand the halftone out
copy and paste halftone into document 

Can you show us an sample file (before / after the steps) from PS?
It sounds like you choose only the dark spots (in grey) but why need to copy / paste to the document?

[issicus]

cool.  thanks.  

looks like you can reduce the alpha channels on CMY to -200% and than just set what ever channel you want to be grey scale on the K channel to 100% and the others to 0. 

Those last two steps are so I can merge the halftone with a non halftone image.  I can figure that out.

notes to the devs?  below:

I'm not sure if this is a glitch but depending on how I merge the halftone it looks like it's applying anti-aliasing, which is bad for me. And for some reason the output of the halftone live filter and the halftone filter in the filters menu is different.

[NotMyFault]

You can deactivate anti-aliasing using the blend options of the layer (cog symbol).

The live filter has an additional option „protect alpha which is off by default.

Normally filters should produce the same result. Can you please share screenshots of the filter settings, and what difference you observe?

Another potential source of difference: the destructive versions impacts only the chosen pixel layer. The live filter impacts the blend result of all layers below (when put above a pixel layer).

[issicus]

I tried forcing antialiasing off and it didn't seem to do anything.  

the blurry one is from the filter menu,  the crunchy one is a live filter than merge visible. 

the settings are more or less the same for the halftones.  One note ,  when I'm previewing the filter menu halftone it looks crunchy until I hit apply.

 

 

[NotMyFault]

Can you please upload the screenshot of the exact settings of the filter (before applying them)?

And I must correct myself: anti-aliasing affects only vector layers.

The halftone filter itself creates antialiasing depending on settings. Cosine with 100 opacityshows no AA, circular / round always shows 1px AA which you cannot deactivate.

in all my tests there is no difference between live/destructive filter.

Assuming you start with fully opaque layers.

 

[NotMyFault]

31 minutes ago, issicus said:

One note ,  when I'm previewing the filter menu halftone it looks crunchy until I hit apply

This happens if the pixel layer has fractional position or stretched DPI.

you need to rasterize it before applying the HT filter to avoid, or ensure (by transform panel) that you have only whole integer position and size 

[issicus]

I don't know maybe its user error.  

If not maybe it's better if they don't "fix" it because my work around might not work anymore.

Not sure if it makes a difference but the file im apply it to is a grey scale I made in a cmyk doc than copied to an rgb document to do the halftone.

[NotMyFault]

I can spot from your screenshot that the layer is rotated.

Again, you need to rasterize the layer before using the HT filter to avoid the blurriness. 

[issicus]

what makes you think it's rotated?  anyway... i'm applying the filter to the same layer.

it doesn't really matter anyway.