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ImageIt · March 26th, 2008

Quote:

Originally Posted by darwinchristian


	I feel like this transfer function in photoshop's output may help me out, based on your post here, but i am not sure how it works. When i go into the transfer values screen, all the values are blank. I have no clue how you came up with the numbers you did.

The transfer function defines a conversion factor between the level of darkness contained in the graphic and transforms it to the levels required to compensate for press gain.

Across the bottom left of the dialog box, you will see a small strip containing a graduated fill. On the left the color is white and on the right the color is black. This represents the colors contained in the graphic.

Above the strip a line chart, which by default is a line going from 0% at the lower left side to 100% on the upper right side. You can either click on the line and slide a point, which results in a number appearing in the text box's on to the right or you can enter a number in the box and have it set the point.

The way i determined my numbers was through physical testing where i printed a graduated screen and determined what change needed to be made. In my testing, i observed that my 10% screen was a little light and that below 10% and that i was loosing he dots smaller than 5%. TO correct this, the 5% screen was changed to 9.1% and the 10% screen to 13.3.

At the other end of the grayscale, anything over 75% was printing 100% black. To compensate, i caused the line to create a flat line from where the left side till i got to 90%. Because i wanted my black to be very solid, i had the line take a sharp curve to 100%. If i were to remake the transfer function, i would probably extend the straight line across the middle 95%, then make an even sharper jump to 100%.

Keep in mind, that this transfer function is unique to my setup and that i'm using a laser printer for film.

Basically, all you want to be able to do is to screen print out a graduated screen and have the printed value match the grayscale value inside photoshop. The transfer function adjusts the photoshop value and change the halftone dot size.

Your first test is to print a sample with a straight line default transfer and determine where the smallest dots first become visible and where the halftones blend to form a solid. These become your end points. In the example i posted, the end points were 5% and 75% which is reflected by the straight line across the mid section of my transfer function.

fred

darwinchristian · March 26th, 2008

Cool. I guess i have some testing to do! A couple other questions if it's no hassle...

How could i create a positive for this "graduated screen"? I imagine since there are 13 steps, with two endponits, that i could create 13 step shades of grey and print them at my regular frequency and screen angle, and analyze the point of complete fill and of no print to adjust my transfer values accordingly... I am embarrassed to say that i don't know how i'd go about creating the grey steps! Any suggestions? I use Corel and Photoshop.

The other question: i am currently saving a tif in photoshop,
placing it in corel,
converting to greyscale bitmap,
printing to device ind ps driver,
opening prn file in gsview,
printing to the R1800 for my positive.
This in order to achieve halftones without a RIP.

Will those transfer values remain on their way to corel and beyond?

or

could i print to a "postscript driver" from photoshop cs3, and bring that ps file directly into GSview?

Edit: By the way, Congrats on the big black shirt!

ImageIt · March 26th, 2008

Quote:

Originally Posted by darwinchristian


	How could i create a positive for this "graduated screen"?

I used illustrator and imported the file into photoshop. I've attached a .pdf version of the photoshop document.

[quote=darwinchristian;260592]
The other question: i am currently saving a tif in photoshop, placing it in corel, converting to greyscale bitmap, printing to device ind ps driver, opening prn file in gsview, printing to the R1800 for my positive. This in order to achieve halftones without a RIP.

Will those transfer values remain on their way to corel and beyond?

or

could i print to a "postscript driver" from photoshop cs3, and bring that ps file directly into GSview?/quote]

For the sake of this exercise, you will be taking option 2. You will be calibrating photoshop to print. To the best of my knowledge, photoshop requires the use of a postscript printer in order to use a transfer function. (i know it used to require postscript). In the short run, you will need to bring your corel files into photoshop to take advantage of the transfer function.

In the long run, postscript allows for transfer functions to be embeded in the postscript .pdf file. Inside a .pdf, the transfer function can be used by any program.

Since i often need to create a white underbase for the process color, i typically create these underbase's in photoshop, so to me there is not downside to bringing the file though photoshop.

fred

rwshirts · March 26th, 2008

We, too, have been experimenting with 4 color process. We had a 1000 shirt, multi-color shirt to print, white cottons, and we decided to give 4 color a try. My son created the screens with Wilflex screenprint software. It did all the work as to screen and color selection. We didn't use a white underbase, since the shirt was white. We intended for the first screens to be practice screens, but we ended up using them for the entire job. We covered quite a few colors...flesh, black, red, green, gold to yellow blend, and it had a soft hand. We printed light to dark....yellow, magenta, cyan, black. 2 strokes on the first 3 colors, 1 on the black. Time was about 12 hours on a 4-station press. The biggest factor, I'd say, is REGISTRATION!!! It has to be perfect!

We want to try a dark shirt 4 color....that will be next week. I will try to post the picture of our finished shirts.

RW

darwinchristian · March 27th, 2008

Quote:

Originally Posted by ImageIt


	To the best of my knowledge, photoshop requires the use of a postscript printer in order to use a transfer function. (i know it used to require postscript). In the short run, you will need to bring your corel files into photoshop to take advantage of the transfer function.

Indeed, as i thought. I will have to play around with this to see if i can't get it to work with what i'm running, until I get my RIP software in a week or two. I'm assuming that i will be able to communicate directly to my printer from photoshop via the RIP. (Definately going to make sure before i purchase it.)

But in the meantime the PDF provided should give me a good starting point to test what my screens are capable of with the setup i have. Good looks Fred, as always. I appreciate you taking the time.

derek

mgatechcameroon · May 6th, 2008

hi printers, i have really been absent on the forum for some time and this was just due to the fact that alot of things were going the oposite direction for me. from all the readings i have done i was almost convinced that process color doesn't work on dark shirts that simulated process color does but for the past four months i have been busy observing and talking to other printers out of the forum and to conclude everything works for everything. it just need some practice , real process, simulated process,index what process really works well for all shirt colours. has some one ever done anything on simulated process or index.

mgatechcameroon · May 6th, 2008

hello guys , thanks for taking theb time of to answer every question ask, what i will like to know is , which inks are guys using for the process prints, is it transparent plastisol inks or water base inks.

ImageIt · May 6th, 2008

Quote:

Originally Posted by mgatechcameroon


	i was almost convinced that process color doesn't work on dark shirts that simulated process color does but for the past four months i have been busy observing and talking to other printers out of the forum and to conclude everything works for everything. it just need some practice , real process, simulated process,index what process really works well for all shirt colours. has some one ever done anything on simulated process or index.

The problem with printing on black, is that the color is black. Since process colors are translucent, if they are printed on black, all you will see is black. Adding a white underbase and the process colors are no longer printing on the shirt, they are printing on the underbase.

Inks can be opaque, translucent or somewhere in between.

Because process color is translucent, the colors blend to form the full rainbow of colors. Opaque inks are called spot colors. These colors use opaque pigments which directly reflects the light off of them. With pigment inks, the ink printed last (on top) will be the color which is viewed.

Process color printing require halftone dots to control color. Printing halftones requires a hire level attention to details than printing using solid areas of color

With spot color, specific colors of ink are mixed by the bucket, rather than with halftone screens. Spot color can be printed with any mesh and without any halftone.

On the flip side of the coin, by using true spot color, no inks need to be custom mixed. The ink comes straight out of the bucket and any that is left can be put straight back in the bucket. Process color requires no special software to separate. Scans, photographs or computer drawings can simply be printed separated.

I use union ink. For printing on dark i use a plastisol white underbase and plastisol process ink.

Between process color and spot color exists any number of combinations of the use of solid, translucent and semi translucent inks. For example, i prefer to use a opaque black for process printing, rather than the process black ink.

As you said, everything works for everything. it just need some practice.

fred

Sheepsalt · 2 Weeks Ago

Hey Fred,

I've always used simulated process to print semi-photo-realistic images using opaque inks, and I've got one now that I think will be better with process.

When you print, does it seem to make a difference what order you lay the colors down? I mean, do you print your white, flash, then print c, m, y, & black wet on wet in that order?

Thanks!

ImageIt · 2 Weeks Ago

White flash, then the process colors.

I used to print, cyan, magenta, yellow, but when i started printing the process wet on wet, out of paranoia i revered to put the yellow first out of fear the darker inks could contaminate the the lighter ink.

I'm currently running a series of tests to see how far it is possible to push process color printing. As i'm pushing past 55 LPI, i've upgraded to a large format epson printer, 355 mesh screen and i'm starting to really like union inks triple pigment process inks.

Prior to moving to triple pigment, i much prefered a spot black rather than the process black, but when i converted the graphic to CMYK, i used minimal black generation, so only what was truly black would be printed with the spot black.

fred

Sheepsalt · 2 Weeks Ago

Very cool, thanks Fred! I'm going to try this tomorrow. The only Process inks I have are Wilflex, so I'll give it a shot with those. Printing on white Hanes Beefy-Tees. so I wasn't planning on printing a white underbase - but I'll make a white plate film just in case.

I followed your process in PS for the films - I'm printing them at 1440 dpi, so set the image resolution to 720 dpi & used <PIXELATE> - <COLOR HALFTONE> filter, set max. radius to '8' & screen angles to 108, 162, 90, & 45, then selected one channel at a time & changed mode to bitmap - 55 LPI, 26 degrees - & printed from there. Hopefully that sounds right? (That's what I use for opaque top colors when setting up simulated process & seems to work fine)

Anyhow, I'll let you know how it works out. The photo is of a swimming pool, & the sim process just wasn't going to look right.

ImageIt · 2 Weeks Ago

The lower the LPI, the easier it becomes.

When i was outputting using my laser printer, i would set the screen setting using the "screen" button in the print dialog under the output print options. When this button is clicked, the default action will be to allow the printer to decide. When i unchecked this button and click "Auto...", the dialog would allow an LPI and a DPI. While i would enter 55 LPI, i would set the DPI to 300, this would cause the values to round down. If the DPI was allowed to be 600, the 55 LPI would round up to 60.6, which was higher than i could hold. When set to 300, the black at 55 would round down to 53.

Now that i am using ghostscript, i can check the "accurate screen" box and 55 will be 55, but ignore why adobe choose not to use it.

What sort of printer you using?

fred

Sheepsalt · 2 Weeks Ago

Mine's an inkjet - Epson 2200 using Fastink for the black & waterproof 13" roll film.

Very interesting about the rounding. I've downloaded gs, but haven't even installed it or looked at it yet, so I'm kind of lost there. I've never used any kind of RIP. For everything else I've done so far with half-tones, I've converted layers to bitmap and dragged them back into the composite image. It's cumbersome, but I've gotten good prints that way - but never process, so now I'm a bit nervous about wasting time & emulsion to get a good image.

ImageIt · 2 Weeks Ago

Ghostscript can defiantly be a PITA! Without a postscript interpreter, RIP or ghostscript, you will not be able to use a transfer function. From my experience, this will result in prints which are too dark. If you plan to output straight from photoshop, you will want to push the midpoint to cause the mid tones to lighten.

If you want to email me the graphic to [email address]

i can try to at least bring the file to where i would print it.

To get where i'm at, i've produced a few dozen shirts and probably 100 impressions. Rather than pushing the graphic to crazy high LPI, i'd suggest backing down to something like a 45 LPI screen.

If your looking to work towards high quality process color, i'd be glad to share my files and film and would encourage you to start printing out your own test files. No matter how much i think i know about printing process color, i still need to make film, screens and prints in order to calibrate my output. Everyones setup if different, so what works for me could be trash for you.

With an epson 2200, would i be correct that you are running sheets and not rolls?

If i can see the graphic, i can also give you a 1-10 rating in the difficulty of the graphic. Most of my work i've posted i'd consider easy. My current test file, i would call the graphic from hell.

fred

Sheepsalt · 2 Weeks Ago

Wow, Fred, thank you! That's very generous. I'll e-mail the raw file I'm working with.

The 2200 has a roll-feed, so I'm using 13"-wide rolls of film.