Canvas profiling

I've recently purchased an Epson 7900 with the intent of printing on more canvas. It's a wonderful printer and does a great job but I get about 1/4 inch of stretch (vertically) with a 20" print, coming out at 19 3/4'. This ,I'm told, is normal do to back tension and I was told by the canvas manufacturer to just resize a bit larger with "constrain proportions" unchecked.
My question is if I send patches away for profiles, should I re-size when printing the patch to make up for the stretch or not worry about it? I don't know if stretch can effect a good profile.

While I'm at it, is there a safe percentage to let the ink run down? I get warnings at 20%. I'm sure Epson would like me to change it but I want to use as much as possible.
Thanks for your help!

Bill, that's a good question. Theoretically, yes, this situation could affect the profile. A print that should be 20" but comes out 19.75" is slightly short. That means the ink is being laid down in a fractionally higher density than it should be, over a given surface area of the media. Depending on the image and relatively how much more ink of what colors is being laid down, this could skew the profiling suite as it reads the patches and calculates things like color transformations and grey neutrality.

Now, .25" over a 20" length is only about 1.25% so the impact to ink density isn't large. Would it noticeable? Hard to say, likely not that visible. If you're going to go to the effort of custom profiling, though, the rule of thumb is to profile with exactly the combination of settings and processes that you use to print. Same print quality, same resolution, same media, same uni- or bi-directional setting, same media type setting in the driver (which can influence ink lay-down as well), etc. So I'd say yeah, go ahead and resize your patch outputs the same relative amount you would use for your production prints. But if it's off by a bit, at this small of a difference it's not likely to be that noticeable.

As for running down the ink carts, I run mine out in my 4880. There's a small risk of a hiccup when exchanging carts, but I believe the 7900 (all 7xxx and 9xxx models, actually) use pressurized lines feeding the print head from a reservoir. The big printers don't pump ink straight from the cart immediately onto the paper. So if the cart "runs out" in the middle of a print job there shouldn't be an issue changing it out on the fly, at which time the print job should carry on. Ink is expensive, and even when the printer says the cart is empty, it really isn't. I don't want to waste any more of it than necessary.

Of course if you have a particularly large & sensitive job, you could switch before starting to avoid the risk of botching an expensive chunk of media. Then switch back for smaller jobs to run down the low cart until it hits "empty"...

Bill,

I didn't resize my targets when profiling (I have the Epson 7880) and they came out fine. I think any amount of difference would be unintelligble to the human eye. Like Royce I run my carts out of ink and have changed ink in the middle of a big print and had no issues. It is not running the ink out of the lines, just the cart so there really is no issue there. I do find it quite irritating that Epson blinks a light on at 20% when you easily print down to 2% or less. I know the money is in the ink but geesh!

Thanks Royce & Les,
That answers both my questions. I just wanted to make sure before ordering any profiles.
I appreciate your help.

Hello Bill,
I run a 7900 and 9900 with all the oem profiles.
I have a Munki and have fooled around a little with profiles for my canvas.
The profiles I get from the manufactures are about as good as they come.
I stopped trying to find something better. Its like a cat chasing its tail.
What canvas are you printing and did it come with a profile?
I use Lexjet Matte,Breathing Colors Lyve and Chromatta White.
All very good products.
You run these models until they are empty. (The printer will stop.)
You put in a new cart and the printer will pick up right where it left off.
You will not be able to see anything on the print.
Where you do run into issues once they get really low is you will be unable to do a pairs clean or a regular
full blown clean when one of the x's is over a color.
Just make sure you have a spare cart of that color,pop it in and do your clean.
After cleaning put the low cart back in and print until it is empty.
I have had low orange and green warnings for 3 months and they are still not empty.
At 20% you should be able to go a long time. The light blacks suck ink and I always have a spare on hand(700ml)
Orange and green you can replace with a 150. I do alot of printing and have 700's in just about all cats except orange and green. You could go 350's.