GO curve for flushing


#1

Hello,

Can the GO curve be edited to produce a series of single channel flush curves? If so, is there an equation to translate the 6-digit figure (30000) into percentages?

Thanks
Paul


#2

The ink curve values are on a scale from 0-65535. So you’ll just need to divide the ink value by 65535 for the percentage or multiply the percentage you want by 65535 to get the ink value


#3

You can create single channel flush curves. I used to do this. It’s a bit easier to do in Windows using the QTR curve creator than it is on a Mac IMHO. However once this technique was published I switched to using it instead:


#4

Thanks for your responses,

I did see this method using the calibration mode in QTR, it seemed to me a bit more complicated then simply editing the GO curves. I wasn’t thinking of using the QTR curve creator, simply renaming the GO curve, opening it with txt editor and typing the values adjacent the appropriate channel. Then printing the RVB 255 file usually used for GO.

With the information Richard provided I’ll be typing 52428 for 80% and 32767 for 50%.

No?

Paul


#5

Those values are correct (or close enough really) you just don’t want to go over 65535 or accidentally type in a negative number…

But, the QTR calibration mode isn’t all that scary. I’ve been using a modified flush target for printing the GO so I can position it directly over the image in print tool when printing multiple targets on a sheet.

Adjusting the calibration mode ink limit slider is a lot easier than editing the GO curve (and doesn’t waste the GO when not needing to cover the whole sheet).


#6

The reason for using a flush image is that you can set the size of it easily so that you don’t print too close to the edge of the paper. If you print too close to the edge of the paper with that much ink on the page, the paper can bend and buckle and hit your print-head which doesn’t make for a fun day.

The same can be done with “printer margins” using a custome paper setup and a modified “flush” curve. I thought about migrating everyone from the old calibration mode method to the new mode but this would have upset the apple-cart I think, and I still would have to teach people how to use calibration mode if they wanted to diagnose their channels.

best,
Walker


#11

The GO is printed wherever there is 255,255,255 in the image, so anything other than white gets ignored when using the GO quad curves (for the traditional 2nd printing). I think your approach might be easier on windows rather than using calibration mode. The image layout window is not easy to manage in the QTRgui like it is in PrintTool.

In print tool its pretty easy to take the flush image for whatever ink you have GO loaded in and resize it with nearest neighbor to fit what you’re trying to cover. Then in the ink limit slider in calibration mode you can just set the value to whatever coverage you need.

Now, if you have printed a final image i would still recommend printing the entire sheet (or as much as will be shown under the mat…) The GO is noticeable at certain angles, so unless you can get it to print right up to the edge of the image without overlapping (or missing) you might end up calling attention to it. But for linearization and printing multiple targets on a single sheet using the flush image is the easiest I’ve found.


#8

Old being (the normal method we currently use), new being a possible new (flush curve) method.

best
Walker


#13

Having slept on it, I think that the ability to resize the GO image on-the-fly is neat. But I don’t really need it for 21x4 target printing. I always print my targets in the same locations down the page and so I created a series of black and white GO templates to print GO in these locations. Even on a Mac, a set of these templates would be faster than having to do an on-the-fly resize every time.


#7

Please explain what you mean by “old” and “new”. Was this a reference to GO printing or purge pattern printing in calibration mode?


#12

Thanks. That makes sense.


#9

Likewise. My understanding is that GO is printed where the GO image is white, and not where it’s black. So I constructed a TIFF that covers the entire page and is black everywhere except where I want GO, and in that area it’s white. I got this trick from Dana some years ago.

The trick is to construct a TIFF that covers every last pixel of the printable area on the page, which is easier in inches than mm, as QTR thinks in inches, at least on Windows.

Richard, are you saying that there’s an easier way using flush images and Cal mode?


#10

Perhaps I’m just old and a bit slow, despite the benefits of a sunny morning in southern Arizona. You are referring to GO printing I take it?