Re: [Gimp-print-devel] Advice on how to add the Epson SL-D700

[Robert K. <rl...@al...>]

On 8/10/21 3:28 PM, Solomon Peachy wrote:
> On Sun, Aug 08, 2021 at 09:49:03PM -0400, Solomon Peachy wrote:
>> Since that value needs to be specified in terms of base_res * 2, which 
>> varies based on the print resolution. it either needs to be specified in 
>> resolution-independent units (and get converted) or has to be pushed 
>> made into a <resolution> parameter.  Which is your preference?
> 
> I have it currently specified in units of base_separation (ie 360).  All 
> resolutions now function properly, so I've moved on to trying to tune 
> this thing a bit better, but there are a lot of knobs:

You might instead want to specify it in terms of the base unit (14400 on most printers)

>  * Inks:  relative intensity of sub-channels
>  * Model: density & dropsizes (per-resolution)
>  * Media: density, subchannelcutoff, YMCbalance, gamma, Ktrans/GCR, HSV maps
>  * External: ICC profile
> 
> If I understand correctly, the drop sizes are specified relative to 
> "largest possible" so presumably one would tune the overall 
> model/resolution density until the media is sufficient saturated, and 
> from there tune each successively smaller drop size until the output is 
> sane. From there you'd add in the subchannels (eg light C/M in this 
> case) and adjust their relative intensity until things look right.

When you tune drop sizes, you don't want to tune them at anywhere near saturation, because
overlapping dots result in non-linear response.  I usually tune them somewhere around 25% IIRC.  For
light inks, it's very important not to be saturated.  You might want to tune those at the smallest
possible drop size so you have the least speckling.

> Then you'd fine-tune the different media types for color balance, 
> relative density, and whatnot. Subchannelcutoff and gamma being the most 
> interesting.

Yep.

> Is all of this ultimately a matter of (systematic) trial and error?
> Am I on the right track here?

That's how I've always done it.

> Lacking any better idea, flipped a coin and used the pro_ultrachrome.xml 
> CcMmYK ink and pro_ultrachrome.xml media definitions as a starting point 
> (which IIUC are printhead-independent) Should I have used 
> f360_ultrachrome.xml (or one of the many ultrachrome_* variants) instead? 

The f360 inks are for printers that use 1/180" spacing, but half of the inks are offset 1/360" from
the others.  For the tuning, it doesn't matter, but don't use the f360 unless you determine that
that printer has that offset.  I would start with one of the ultrachrome ones.

> (I noticed that the pro_* stuff seems to have a 1.0 gamma where the 
>  f360_* stuff seems to have a 0.92 gamma..)

Not sure why, to be honest.

> For the resolution-specific density/dropsizes, I started with the 
> pro_x600 baseline which turned out to be quite wrong but I guess I had 
> to start somewhere...

I wish I could say I have a more scientific procedure, but not really.