Is there a way in GIMP to take any JPG image and have GIMP output 4 color seperated images as individual CYGK or RGB or choosable colors? I want to make a silk screen with a real complicated color image and I thought it could be possible to
break down the photo into the silk screen inks and then make 4 different ink screens with
emulsifiers by each color of the photo. I find pallettes and tools and such but can not make any sense of how to actually accomplish the task.
Also... what about shading.
Does gimp do shading...like newprint shading with dot densities? Is there a technical name for this kind of shading where a black and white image can appear
as shading by dot saturations and not actually by having shades of grey?

I'm real new at this so any information woul dbe greatly appreciated.

Rob

Look for the Decompose plugin - Colors>Components>Decompose... CMYK - you'll get an image with 4 black and white layers. Then you can save each layer as separate files you can use for silk screen. To make shadings with dots, use Filter>Distorts>Newsprint and play with the settings ;)

On 11/6/06, graffoo wrote:

Look for the Decompose plugin - Colors>Components>Decompose... CMYK - you'll get an image with 4 black and white layers. Then you can save each layer as separate files you can use for silk screen. To make shadings with dots, use Filter>Distorts>Newsprint and play with the settings ;)

Is it my imagaination, or are the CMYK layers inverted?

I'm using GIMP version 2.2.13

Chris

On Monday 06 November 2006 09:32 pm, Chris Mohler wrote:

On 11/6/06, graffoo wrote:

Look for the Decompose plugin - Colors>Components>Decompose... CMYK - you'll get an image with 4 black and white layers. Then you can save each layer as separate files you can use for silk screen. To make shadings with dots, use Filter>Distorts>Newsprint and play with the settings ;)

Is it my imagaination, or are the CMYK layers inverted?

Yes, for printing purposes they are inverted after the "decompose" plug-in.

The amount of ink is marked in each pixel from 0 to 255 - so, if an image has some pixels with "zero yellow" (for example, white pixels) - the output of the decompose plug-in has this as "zero yellow ink"- meaning black. if it where full yellow, it would be full intensity - showing White.

In pratice, you just have to invert that.

You can't however expect color accuracy with that plug-in. That is - you will have variations on the color you see on the screen and the color you get if you use the decompose plug-in, invert each resulting image, print that as a screen, and recompose the colors.

you may also want to increase the pixel quantity in your image, before using the newsprint plug-in. Your target printing process have an ideal "lpi" number - arrange your work so that you have these lpi in the final image for each color.

Another way of doing this work you might find usefull is using the GIMP channels instead of layers for compositing your final image.

Just create a channel for each ink color you intend to use, and later apply the newspirint plug-in ont these channels.

As for separating, let's say, "dark blue" in a separate channel from a normal RGB image, I can think of the following procedure, which would have to be written as a plug-in:

duplicate image, flatten-image, duplicate layer, color to alpha(remove desired channel color, on the underlying layer), set upper layer to 'difference' combine mode, copy visible, paste as new layer, dessaturate, copy, create new channel, paste on new channel.

Perceive taht whatever you do, the "dessaturate" step will modify the finalc composition of your image you should spend some trial and error either in that step, or modifying the curve of the final channel.

Either way, I'd like to hear how you are doing when using GIMP this way.

Regards,

js
->

I'm using GIMP version 2.2.13

Chris

Either way, I'd like to hear how you are doing when using GIMP this way.

To be 100% honest, I still haven't done too may separations with GIMP yet. I'm slowly gathering all the bits and pieces necc. to replace AI and PS with Inkscape and GIMP - but it's taking a while :)

I have used spot channels in GIMP, and they behave as expected. The 'halftone/newsprint' plugin seems a tad noisy to me, so for haltones I'm saving as PS, inserting my haltone freq/angle into the PS file, and "printing" through ghostscript. (it here a way to use GS as a plugin for GIMP...?)

It's a work in progress - I'll let everyone know how I make out...

Chris

----- Original Message ----
From: rob
To: gimp-user@lists.XCF.Berkeley.EDU Sent: Monday, November 6, 2006 4:25:48 PM Subject: [Gimp-user] how to break down a photo into printing colors and newsprint shading

Is there a way in GIMP to take any JPG image and have GIMP output 4 color seperated images as individual CYGK or RGB or choosable colors?

I'm not sure I understand what you're after but take a look at Image->Mode->Decompose

Hi Rob,

On 11/7/06, gimp-user-request@lists.xcf.berkeley.edu

Message: 4
Date: Mon, 06 Nov 2006 03:25:48 -0500 Subject: [Gimp-user] how to break down a photo into printing colors and newsprint shading
Message-ID:

Is there a way in GIMP to take any JPG image and have GIMP output 4 color seperated images as individual CYGK or RGB or choosable colors? I want to make a silk screen with a real complicated color image and I thought it could be possible to
break down the photo into the silk screen inks and then make 4 different ink screens with
emulsifiers by each color of the photo. I find pallettes and tools and such but can not make any sense of how to actually accomplish the task.
Also... what about shading.
Does gimp do shading...like newprint shading with dot densities? Is there a technical name for this kind of shading where a black and white image can appear
as shading by dot saturations and not actually by having shades of grey? I'm real new at this so any information woul dbe greatly appreciated.

I think there is a CMYK plugin for GIMP. May be that's what you need. May be Filter/Distord/Newsprint is what you need for newsprint shading.

--
Asif

Interesting...newsprint filter does make the dots resolutions. OK
Looks like all the pieces are here except for..... I still have not figured out how to save out
ONE layer at a time while in the CYMK.jpg 4 layers greyscale image. Can anyone give me the instruction to accomplish this one simple task? I'm stumped. I can't find any way to isolate single layers and each layer is the
individual seperated colors I desired to work with. Such a tease. So close but still no cigars.

Asif Lodhi wrote:

Hi Rob,

On 11/7/06, gimp-user-request@lists.xcf.berkeley.edu

Message: 4
Date: Mon, 06 Nov 2006 03:25:48 -0500 Subject: [Gimp-user] how to break down a photo into printing colors and newsprint shading
Message-ID:

Is there a way in GIMP to take any JPG image and have GIMP output 4 color seperated images as individual CYGK or RGB or choosable colors? I want to make a silk screen with a real complicated color image and I thought it could be possible to
break down the photo into the silk screen inks and then make 4 different ink screens with
emulsifiers by each color of the photo. I find pallettes and tools and such but can not make any sense of how to actually accomplish the task.
Also... what about shading.
Does gimp do shading...like newprint shading with dot densities? Is there a technical name for this kind of shading where a black and white image can appear
as shading by dot saturations and not actually by having shades of grey? I'm real new at this so any information woul dbe greatly appreciated.

I think there is a CMYK plugin for GIMP. May be that's what you need. May be Filter/Distord/Newsprint is what you need for newsprint shading.

On 11/6/06, rob wrote:

Interesting...newsprint filter does make the dots resolutions. OK
Looks like all the pieces are here except for..... I still have not figured out how to save out
ONE layer at a time while in the CYMK.jpg 4 layers greyscale image. Can anyone give me the instruction to accomplish this one simple task? I'm stumped. I can't find any way to isolate single layers and each layer is the
individual seperated colors I desired to work with. Such a tease. So close but still no cigars.

Hide all unwanted layers, then do file > save as. If you choose PNG for exmaple, GIMP will merge the visible layers and save a copy. Repeat for each layer.

Chris

Hi,

On Mon, 2006-11-06 at 20:28 -0600, Tim Jedlicka wrote:

Is there a way in GIMP to take any JPG image and have GIMP output
4 color seperated images as individual CYGK or RGB or choosable colors?

I'm not sure I understand what you're after but take a look at Image->Mode->Decompose

I wouldn't use Decompose for this but rather the "separate" plug-in which does the job according to a CMYK color profile in contrast to the rather naive implementation in Decompose.

http://www.blackfiveservices.co.uk/separate.shtml

Sven

This advice to not use DECOMPOSE and to use a plugin from blackfiveservices.......

Is the standard GIMP DECOMPOSE implementation so bad that it will not produce images
that are worthy of using for screen printing?

I like bells and whistles as much as the next guy but I try to use the base software when possible
so I would like to stay away from plugins if DECOMPOSE will do the desired task.

Sven Neumann wrote:

Hi,

On Mon, 2006-11-06 at 20:28 -0600, Tim Jedlicka wrote:

Is there a way in GIMP to take any JPG image and have GIMP output
4 color seperated images as individual CYGK or RGB or choosable colors?

I'm not sure I understand what you're after but take a look at Image->Mode->Decompose

I wouldn't use Decompose for this but rather the "separate" plug-in which does the job according to a CMYK color profile in contrast to the rather naive implementation in Decompose.

http://www.blackfiveservices.co.uk/separate.shtml

Sven

Hi,

On Tue, 2006-11-07 at 12:47 -0500, rob wrote:

Is the standard GIMP DECOMPOSE implementation so bad that it will not produce images
that are worthy of using for screen printing?

I like bells and whistles as much as the next guy but I try to use the base software when possible
so I would like to stay away from plugins if DECOMPOSE will do the desired task.

Just as I said, the RGB to CMYK transformation that the Decompose plug-in uses is rather naive. It doesn't know about the printer you are going to use, nor does it know about the inks or the paper. Without that information, it can hardly do a good job.

Sven

This advice to not use DECOMPOSE and to use a plugin from blackfiveservices.......

Is the standard GIMP DECOMPOSE implementation so bad that it will not produce images
that are worthy of using for screen printing?

"Screen Printing" is too broad a subject. If you're preparing screens for 4-color process, I doubt the decompose mode nor the CMYK plugin will be adequate. I would let the person actually doing the printing handle that. OTOH, if you're going to be making a file for printing spot colors, I'd skip CMYK/RGB altogether and use channels - 1 per ink color.

There are tutorials on screen preparation out there - most focus on photoshop, but you can do most of the same things in GIMP.

Chris

PS - maybe you can provide some more detals about what it is you're trying to do?

I thought I had made this clear that the desired task was to use green muck photo emulsifier
that you smear on a silk screen and then lay a black and white image of anything on the muck and shine light on it and the black in the image blocks light while the light getting into the green muck causes it to harden. You then rinse off the remaining muck and you have a perfect transfer of the black and white image into
a T shirt silk screen.
Do that a few time with a few colors and you have pretty T shirts. So I figured GIMP should be able to make the color seperation and the newsprint shading within good to great results without having to resort to adding in any missing GIMP features. SO far I have gotten great advice how to make the color seperated individual images that can be printed onto overhead transparancy film.

The question of how to color seperate into individual inks seems to be up in the air now and subject to
experimentation.
To use RGB or CYMK or channels.
I have not played with channels yet but did get CYMK individual images.

Thankyou to everyone who has contributed advice. I am running KNOPPIX debian linux installed to hard disk which came with GIMP but does not have help installed so even though my help is crippled I got ALL this help from the email list.
Rob

Chris Mohler wrote:

This advice to not use DECOMPOSE and to use a plugin from blackfiveservices.......

Is the standard GIMP DECOMPOSE implementation so bad that it will not produce images
that are worthy of using for screen printing?

"Screen Printing" is too broad a subject. If you're preparing screens for 4-color process, I doubt the decompose mode nor the CMYK plugin will be adequate. I would let the person actually doing the printing handle that. OTOH, if you're going to be making a file for printing spot colors, I'd skip CMYK/RGB altogether and use channels - 1 per ink color.

There are tutorials on screen preparation out there - most focus on photoshop, but you can do most of the same things in GIMP.

Chris

PS - maybe you can provide some more detals about what it is you're trying to do?