My point is that when using a Perceptual soft proof, the same big pile of new RGB numbers would be sent to the device whether I did the conversion or they did it. At least that's how I see it, we're using the same profile, and doing the same conversion, and using the same Perceptual intent.
Yes, assuming they used the same profile, CMM, BPC etc. And any hope of applying output specific edits after conversion is off the table here.
Another way to put it is that they offer two options for a file soft proofed with the Perceptual intent. Either they automatically convert the file from its working space using the Perceptual intent, or I do it manually and send an untagged file and give them special instructions NOT to do the same thing automatically.
I’d go Option 2. I want to fully control the conversions and post editing, I want to know that the output values are being sent to the printer that I generated.
Actually you could say WCI's PrintLab service does both, as they don't "demand" a working space but offer options to send either a file with a working space -OR- an untagged file converted to the printer profile.
I was speaking generally of all labs, not WCI specifically in terms of best practices.
b) When sent an untagged file already converted to the printer profile, as instructed they will not convert before sending it to the printer.
Again, I’d use B. And it should make no difference if I use RelCol here.
I want to use a) above when soft proofing with Perceptual because I don't need to convert, store or save a special iteration in order to maintain the Perceptual intent. And I want to use b) when soft proofing with RelCol so my file won't be automatically and inadvertently (double) profiled with the wrong (Perceptual) intent.
That will (should) work.
Regardless of how goofy this all sounds, what I need to know is "what is wrong" about sending them a file in a working space when I soft proofed using Perceptual and we know they will convert using Perpetual, and we know they will convert with the same profile I would use to convert.
What would be goofy is a lab demanding you use Perceptual for workflow B (it would make no difference). What’s super goofy is providing you a profile you can’t use.
Would the print not be the same regardless of who converted the file?
Unless you hit a bug with some CMM (and you’d have to ask the lab what CMM they use), that option would not make a big difference. But Black Point Compensation could. If the didn’t use it and you did, there could be an issue or lets say a disconnect between you and them doing the conversions. If you wanted to post edit the image after conversion, well then you have to use option B.