Tutorial

Workflow

ScreenSeps is not like any other separation software. It runs in your browser and is available to you from almost anywhere.  It simply handles all art the same way: with ultimate flexibility and simplicity. It is also built for minimum tweaking after separating.

The seps created with ScreenSeps are not meant to be incorporated in a design—although this is certainly possible. ScreenSeps seps are meant to be printed. Using ScreenSeps should be the last step before film output—or some curve tweaking while it’s still in beta.

If you input your finished art, your output will match as close to your intentions as possible. You do not ever have to worry that your art will be too hard to separate, because ScreenSeps makes every single separation extremely easy. You can design anything you like, as long as you keep an eye on your usage of colors. To print a rainbow still requires more inks than a grayscale image, of course. Still, even if you want to squeeze as much color out of as few inks as possible, ScreenSeps will allow you to do that.

In short, to get the best results, finish your art in your design software to the point where you are completely happy with it and ready for printing. Only then move on to the next stage of separation. If you are unsure on whether you want art changes, then make sure to finish those first. Any changes made after separating will many times harder to do if color accuracy is important.

 

Preparing your art

In order to get awesome prints, you have to first have awesome art. Assuming you have found some way to get this art into your favorite software, it’s now time to get it ready for print. In order to do this right, there are a few things that have to be taken into account.

First, make sure the quality of the art is great. Vector is always best, but it is certainly not required. Many screen printers think that if it isn’t vector, it’s not worthy for print. This is a myth, however. Your art will print great as long as the resolution is high enough. What this means in terms of resolution depends on your art work.

If you have sharp, smooth lines in your art, you’ll want these to be rendered at at least 150 dpi. Note that this is a bare minimum and 200 dpi is better and 300 dpi is plenty. You should not need more than 300 dpi.

If you have photographs or similar art, with no hard lines, you do not need nearly as high of a resolution to start with, because blurring doesn’t visually change the image much. Any smooth gradients can be used even if they have a low resolution. It is still important that you resample your art to 200 or 300 dpi, so you can control and inspect exactly what the final image will look like.

It is important to keep an eye on the vibrancy and saturation of colors in your art. It is perfectly fine to use muted colors if the art calls for it, but many times screen printers favor vibrant, saturated colors. Since ScreenSeps is the last step before printing it’s important to make sure the art you have is just the way you want it on the shirt.

 

Exporting for ScreenSeps

ScreenSeps prefers you load un-interlaced PNG images. Interlacing is simply a way to change the order pixels are saved in a file. ScreenSeps is faster when they are saved from top to bottom so it can stream the pixels through the engines. This allows it to process enormous images. If you drop images that are not PNG files, they are automatically converted to PNG. Of course, as is always the case with format conversions, sometimes the conversions lose some quality, so it’s always better to convert to PNG yourself. You’ll know exactly what you get and ScreenSeps won’t have to convert it, which saves a few seconds every time.

If your art is in a vector format, you’re in luck. Or maybe it wasn’t luck and you just spent hours recreating art a customer sent to you as a blurry and blocky JPG. Whatever the case may be, ScreenSeps prefers PNGs, so it’s best if you convert it yourself somehow.

Anti-Aliasing

Before and when you export your art, you should turn off any anti-aliasing of vector elements. It makes it look ugly when you zoom in. You can see jaggies and lines are not smooth. But this is just what you want because you’re not trying to get it to look good on screen. You want it to be great on a shirt.

When you print to a shirt, it’s important to not have the gray/partial coverage pixels created by anti-aliasing. If you do have anti aliasing on, it will produce a ragged edge due to halftoning trying to accurately generate the partial coverage. The ugly jaggies are only visible on screen and only when you zoom in. When printed on a shirt, the 300 dpi makes sure that any pixels are invisible.

Note that when up-sampling an image that has low resolution to 200 or 300 dpi, you may or may not want to turn on anti-aliasing / resampling. See the art preparation section for more info.

Transparency

Make sure that the PNG you export does not have a background. PNG images support transparency, which means that they need not be rectangles, but can be any shape. ScreenSeps will take this into account when separating your art.

There is no need to produce two images composited against a different background like needs to be done in some other software. It is important that you remove any such backgrounds yourself, however. If your art is already flattened against a background, you will have to erase the background yourself. Sometimes this can be done with the magic wand tool of your favorite software, but only if the edges of your art are hard edges. PhotoShop has a tool called the Background Eraser, which can be very helpful in erasing backgrounds.

PhotoShop

Select 'none' for all text object anti-aliasingStart out by saving a copy of your art. You’ll be butchering this file so if you do not make a copy, your original may be accidentally destroyed.

Make sure the anti-aliasing on all text objects is set to ‘none’. Doing this prevents text from having ragged edges on print. It’s counter-intuitive but it’s the way it works.

aliased text detail

Next, change the resolution of your image to 200 or 300 dpi. Select Image→Image size and enter ‘300’  in the ‘resolution’ field and select ‘pixels/inch’ from the unit drop down. You can also go with 200 dpi if your image is physically large. Assuming you’re up-sampling (enlarging), select ‘Bicubic Smoother’ for the resample function, unless you have hard lines. If you have any hard lines, select ‘Nearest Neighbor’.

Make sure that the physical document size is correct, in inches or cm. Having the wrong physical size specified will produce issues down the line (starting with not enough or too many pixels, which is your resolution).

Next, if you used ‘Nearest Neighbor’, select any areas that look ‘pixelated’ but should be smooth, and blur or smart blur them. Make sure to keep any ‘jagged edges’, unless they are too big (visible when zoomed out). If they are too big, start over and vectorize your art. See preparing your art.

Then, delete all the layers that you do not want to see on the final shirt. This includes any background. If you did it right and your art is not a big rectangle, then you should see some checker background, which is a way to indicate there’s nothing there.

Make all the remaining layers visible. Merge all the layers by clicking Layer→Merge Visible.

Save your file (do not overwrite the original!). Now you can export it as a PNG. Click File→Save As…

PhotoShop save as PNG dialog

PhotoShop PNG options dialogSelect “PNG” from the format drop-down box. Make sure to note where you save the file and what the name is. Using a name like “my art final version.png” is a good idea, so it’s clear it’s the merged and un-editable final version.

Next, make sure the interlace option for PNG is set to ‘None’ or ScreenSeps will not be able to use your image.

Click ‘OK’ and your art is ready for separation!

CorelDRAW

Select the items you want on the shirt. If you want it all, hit Ctrl-A. Make sure that the physical size is correct, in inches or cm. Having the wrong physical size specified will produce issues down the line (starting with not enough or too many pixels, which is your resolution).

Click File→Export.

Enter a file name and location and select “PNG – Portable Network Graphics” from the “Save as type” drop down box. Make sure to note where you save the file and what the name is. Using a name like “my art final version.png” is a good idea, so it’s clear it’s the merged and un-editable final version. Click ‘Export’.

CorelDRAW convert to bitmap dialog

Make sure  your resolution is 200 or 300 dpi, you have Anti-Aliasing unchecked and you have Transparent Background checked. Then click OK.

CorelDRAW PNG expert dialog

In the next dialog, select ‘none’ for the Transparency option, even though that makes no sense at all. The output will have alpha transparency anyway. Also, make certain that ‘Interlace Image’ is unchecked. If this is checked, ScreenSeps will not be able to use your image.

Click ‘OK’ and your art is ready for separation!

Corel PHOTO-PAINT

Click Image→Duplicate… to make sure you have a fresh image. Uncheck ‘Merge objects with background’.

Your image should be 200 or 300 dpi. You can resample (Image→Resample) it to get there, but this will blur your image. If you have sharp lines, such as text, you should not resample. If you have an image with no sharp lines, such as a photograph, it may be beneficial to resample with anti-aliasing enabled. If you have sharp lines, you should have at least 150 dpi to being with or your print may turn out visibly pixelated.

Make sure that the physical document size is correct, in inches or cm. Having the wrong physical size specified will produce issues down the line (starting with not enough or too many pixels, which is your resolution).

Corel PHOTO-PAINT objects dockerDelete any objects you do not want to appear on the shirt. Select all the remaining objects and click “Combine Objects Together” Combine objects together.

Now you have to perform a trick to get the transparency correct in your output.

  • Make sure your one remaining object is selected.
  • Click Mask→Create→Mask From Object(s) (or hit Ctrl+M)
  • Click Object→Matting→Threshold
  • Set the level to 1 and click ‘OK’
  • Click Object→Combine→Combine All Objects With Background (or hit Ctrl+Shift+Down Arrow)

Your image is now flat, with a correct mask. Your colors could look strange where you have partial transparency. Ignore this.

Click File→Save As… Enter a file name and location and select “PNG – Portable Network Graphics” from the “Save as type” drop down box. Make sure to note where you save the file and what the name is. Using a name like “my art final version.png” is a good idea, so it’s clear it’s the merged and un-editable final version. Click ‘Save’.

Corel PHOTO-PAINT PNG export dialog

In the PNG export dialog, make sure to select Masked Area for “Transparency”. If you cannot select it, it means you have no mask. If you performed the trick above correctly, you should always have a mask. In any case, unless your art is rectangular and fills the entire image, this is probably not what you want. Finally, make certain that ‘Interlace Image’ is unchecked. If this is checked, ScreenSeps will not be able to use your image.

Click ‘OK’ and your art is ready for separation!

Your account

ScreenSeps has a powerful account handling system. If you create projects without being logged in, they will be added to a temporary ScreenSeps account that is automatically created for you. When you close your browser, this account essentially is deleted including all its projects. However, if you sign up or log in to your account, all the projects inside the temporary account will be added to your account. This way you can get started immediately without logging in, but you can still save your projects if you decide later what you have is worth keeping around.

You can browse your projects at any time by clicking the ScreenSeps projects button button. In the top right you can ScreenSeps search projects to quickly find the one you want.

If you click on a project image, it will load right away. You can change the name by simply clicking it, and you can delete it with the ScreenSeps delete project in the corner.

Creating a new project

If you have the Projects window open, close it. Drag your image from your desktop, from a folder or from a web page into your browser and drop it. A project will be created automatically. Your art is uploaded, converted, resampled, quantized, downloaded, colors are analysed and inks generated, a sep engine is generated from the inks and compiled, and your image is instantaneously separated on your screen. All this complexity is fully automatic. Your project is now available in the Projects window.

At this point you may be ready to download your seps. It really depends on whether you are happy with the colors that ScreenSeps picked for your art. If you find the choice good, then go ahead and download your seps. Otherwise, change your colors around until you’re happy.

The work space

ScreenSeps workspace

The work space of ScreenSeps is designed with simplicity in mind.

In the top right you’ll find your account controls, where you can log in, sign up, change passwords, etc.

On the bottom you’ll find a list of thumbnails. When you hover over them, they enlarge for easy inspection.

From left to right, they are:

  • Original image
    Click to see your original image. This version is converted to a format suitable for the browser and your GPU, so it will have a different resolution. The colors, however, should be similar, although slight blurring may cause colors to appear that are not in the original art. A black and white image may for instance have some grays in the preview. Note that your original image is stored on the server and this original is the image that will used to generate your seps.
    Clicking the original thumbnail does the same thing as hiding all color separations. If no color separations are visible, the original image will show.
  • Preview
    Click to see a composited preview of how it would print on a shirt. If you are zoomed out and you have enough colors in your palette, you may see no change between the original and the preview. However, if you zoom in, you’ll see halftone dots appear, which you that you are in fact looking at the separation preview.
    Clicking the preview thumbnail does the same thing as showing all color separations.
  • Shirt color
    Double-click to change the color of the shirt in the preview.
  • White base
    Click to toggle the white base visibility in the preview.
    Right-click to show only the white base and hide all other separations.
  • Ink color palette (multiple thumbnails) in print order
    Double-click to change the ink color.
    Click to toggle the visibility in the preview.
    Right-click to show this one and hide all other separations (including the white base).
  • Add color / delete color
    Click to add a color
    Drag an ink thumbnail here to delete it. It will turn into a recycle bin as soon as you start dragging.

Region zoom

Use the left mouse button to ‘lasso’ a rectangle around your area of interest and ScreenSeps will zoom in to this region.

Mouse zoom

You can use the scroll wheel on your mouse to zoom in and out. Zooming will occur around the mouse cursor position, so place the cursor where you want to zoom.

Pan

Use the right mouse button to move around your image.

Changing inks

The great power of ScreenSeps lies in its ability to conform to any colors you want to separate to. If you want to use 5 grays to print a black and white photo, this is just as easy as printing using 12 custom colors or just 2. As a matter of fact, any image can be printed with just a black and white ink to print it in black and white.

Because of this, there’s never any merging of channels. After all, if you only generate the channels you want, there’s never a need to merge anything. As soon as you add, remove, change or even reorder a color, the entire color separation engine is rebuilt from scratch and the whole image is re-separated from the original. This all happens in the blink of an eye.

This concept is very important for ScreenSeps and it’s one of the great differentiators between ScreenSeps and other software. In other software, when you pull a new color, it’s in addition to the colors you have already pulled. In ScreenSeps, when you add a color, say orange, when you already have colors, say red and yellow, then the new color will disappear from the colors that were already present. In reality, it is not removed, but instead the image is re-separated from scratch with a brand new custom separation engine.

Similarly, when you delete colors, they are not actually removed from the image. A new separation engine is built without that color and the image is separated from scratch.

When you move colors around, the separation engine is also rebuilt. Separations are built to take into account the separations above it. For instance, a mid-gray may be formed by printing a lot of black with a 50% white on top. If now the white is moved to the bottom, it becomes much denser and the black becomes 50%. The exact math is very complex, however, so it’s not easy to give a quick example.

Adding

ScreenSeps add ink buttonTo add a separation (or ink) color, just click the “add color” button.

A dialog box will open where you can select a color. Select a hue with the hue wheel, and then determine your saturation and brightness (value) with the center square. Then, on the right, you can type in exact RGB or HSV values, and you can choose from colors in color sets, which you can pick from the drop-down at the top.

ScreenSeps color selector

ScreenSeps color in setIf you want ScreenSeps to remember the specific color from your color set, including its name and set name, then you should take care not to change the color after selecting it from the color list. If you currently have a set color selected, this will be indicated in the color preview box.

Removing

ScreenSeps delete inkTo remove a color, simply drag it to the right and drop it into the recycle bin (which won’t appear until you start dragging). Note that removing a color does not remove any color information. For instance, if you have a red, a yellow and an orange color, and you delete the orange, the orange colors in the image will automatically be mixed from red and yellow instead. It’s perfectly fine to delete any color. You can always get it back by simply re-adding the color.

Changing

Changing a color is as easy as double-clicking its thumbnail. The color selector opens where you can change the color. Note that you can also change the t-shirt color.

Reordering

To reorder colors, simply drag them to the desired location. Many screen printers have preference as to what order separations should be printed in. It is very important not to only print in this order, but to also make sure you separate specifically for this print order. When you change the order of the colors, ScreenSeps will adjust for the print order. Note that the print order is from left to right. ScreenSeps orders the colors in order from dark to light by default.

Optimizing

ScreenSeps gives you the opportunity to dig in and see what your art will look like on a shirt. It also gives you the power to change your mind. Since none of the changes you can make change the original image, you can play with the colors until you are happy with the output.

There are different and opposing goals that we try to meet when separating. These goals are mostly separation accuracy and printing cost. To get accurate seps, more colors are needed, but to get cheaper prints, we need less. Some manual printing presses don’t have room for more than 4 colors, so in this case it’s vital to squeeze as much range out of as few colors as possible.

ScreenSeps is incredibly accurate and can produce separations to print photographs with people’s faces in as little as 3 colors. That sounds less crazy when you realize the colors are red, orange, and black, and the prints are on white shirts. If you want to print this on black shirts, you’ll want an underbase, but you can drop the black, so this means you can still print this on a 4 color press.

ScreenSeps also has special color handling that processes colors in a physically accurate way. This allows it to ‘make due’ with less colors. For instance, there are few reasons why you should need to use many grays to print a black and white photo. Just printing white on black or black on white often is enough. This reduces the print jobs from up to 5 colors down to a single color, which allows for a huge increase in setup speed and printing speed.

If you want to leave out printing a black separation on a black shirt, then make sure the black color is right after the white base. Separate as usual and then simply do not print the black separation.

If you want to leave out printing the white separation on a white shirt, then make sure to move the (highlight) white right next to the white base. This will reduce the density of the paler colors so as to show more shirt through and this is important to get a good-looking print. You can then separate as normal and when printing, skip both the white base and the (highlight) white.

Note that ScreenSeps does not care what order you put your colors in. Your highlight white might be the first color or the last or anywhere in between. All colors are treated equal.

Getting your seps

If you are happy with how your seps look on screen and you have the desired colors in the order you want, then you can get your seps by clicking the ScreenSeps download seps button. ScreenSeps will start separating your art. When the separation is done, your seps are automatically downloaded to your computer. Depending on your browser and settings, you may be asked for a download location, or the download may start immediately. You can open this file by simply double-clicking it. Inside you will find your separations as film-positive PNG files.

Output

To output your separations, you can use a number of different software setups. You can print it through a RIP (raster image processor) or you can render halftones yourself and print them.

RIPs have a few advantages. One of them is that it’s a quick way to get halftones and you don’t have to figure anything out. Another advantage for some RIPs is that they may talk to your printer on a low level which may enable them to use all ‘colors’ of your printer to print black ink by simply placing black cartridges in the color slots of your printer. This may save a little money, but more importantly, it allows for faster printing and having to refill your ink less often, both of which enhance your workflow.

That said, a RIP is not necessary, since you more than likely already have the software to generate your own halftones. RIPs can be very expensive indeed, so if you feel it’s not wise to invest in a RIP, it’s great to have alternatives, including free ones.

If you’re using a RIP, then simply load the seps into your favorite graphics program and click the print button.

PhotoShop halftones

Open your sep.

Click Image→Duplicate to create a new image from this, so you don’t modify the original. Close the original.

Click Image→Mode→Grayscale and make it gray (it should be gray already but it doesn’t hurt to make sure).

Click Image→Adjustments→Curves to adjust the curves. ScreenSeps does some dot gain compensation but this feature is (at the time of this writing) experimental and needs to be tweaked. If you have experience in screen printing, you may be able to eyeball it. Otherwise, some test prints may be necessary. When in doubt, just skip this step. Your prints should be reasonably good without any modification. Note that in order to compensate for dot gain, you should move the line down to lighten the film.

Click Image→Image size. Make sure the image size in inches is correct. Then put ‘1200’ in the ‘Resolution’ field. At the top of the dialog it should display the size of the new image in megabytes. If you feel it’s too huge for your system, you may lower it to, say, 900 dpi. Make sure your new dpi is a whole multiple of your old dpi. The lower your dpi here, the less quality your dot shape will be, but high dpi does require lots of memory.

Select ‘Nearest Neighbor’ from the resampling drop-down. You don’t want to blur your image. Increasing the resolution is for the quality of the dots themselves. Your film is already supposed to be at a high resolution.

Click ‘OK’ and let PhotoShop resize your image. It’s now officially enormous.

Next, click Image→Mode→Bitmap…

Select ‘Halftone Screen…’ from the drop-down box. And click ‘OK’.

Decide on your frequency. Use 50 or 60 lpi (lines/inch) if you’ve got lots of control on press and you can squeeze out small dots. Use 35 or so if you’re okay with seeing your dots but want to be sure it turns out good. Also take into account that you should not have more than 1/5th the halftone screen lpi compared to your screen mesh ruling. So if you have a 305 mesh, you can go up to 60 lpi, but if you have a 120 mesh, 35 lpi is pushing it. What will happen is that your dots are too small to hang on to the mesh and will wash out.

Decide on your angle. This one is totally up to you. Lots of screen printers print at 22.5° for all films. You cannot make real rosette patterns (0°+x, 30°+x, 60°+x) with more than 3 films. CMYK printing cheats by putting yellow at a weird angle because yellow is the least visible. Printing with the wrong angles guarantees moiré on press which is ugly. If you print all films with the same angle, then you don’t have to think about it, but it may still not be the best way to print. When in doubt, use 22.5°. If you have only 3 colors, you can go ahead and put them at 15°, 45° and 75° for real rosettes. Make sure your ‘most dominant color’ is the one you’re printing at 45°, because it’s easier on the eyes.

Select ellipse as the shape, because that’s what everybody else does. Use ‘line’ for an artistic twist.

Click ‘OK’.

You now have a halftoned film. The resolution of this bitmap is exquisite and it’s close to the maximum resolution your printer can print. You can make the dots even smoother, however.

Click Image→Mode→Grayscale because you can’t run any filters on a bitmap.

Then click Filter→Noise→Median and enter a radius of 1 followed by ‘OK’.

Click Image→Mode→Bitmap. Select ‘50% threshold’. Click ‘OK’.

Save your halftoned film.

You can print this with any printer, with or without a RIP. Select Photo quality if you don’t use a RIP so it deposits enough ink.

 

Corel PHOTO-PAINT halftones

Open your sep.

Click Image→Duplicate to create a new image from this, so you don’t modify the original. Close the original.

Click Image→Convert to Grayscale and make it gray (it should be gray already but it doesn’t hurt to make sure).

Click Adjust→Tone Curve to adjust the curves. ScreenSeps does some dot gain compensation but this feature is (at the time of this writing) experimental and needs to be tweaked. If you have experience in screen printing, you may be able to eyeball it. Otherwise, some test prints may be necessary. When in doubt, just skip this step. Your prints should be reasonably good without any modification. Note that in order to compensate for dot gain, you should move the line up to lighten the film. You can select ‘Gamma’ for the ‘Style’ option to get a curve that is close to the shape of a dot gain adjustment curve.

Click Image→Resample… Make sure the image size in inches is correct. Select ‘inches’ from the drop-down box to verify this. Then put ‘1200’ in the ‘Resolution’ fields. At the bottom of the dialog it should display the size of the new image in megabytes. If you feel it’s too huge for your system, you may lower it to, say, 900 dpi. Make sure your new dpi is a whole multiple of your old dpi. The lower your dpi here, the less quality your dot shape will be, but high dpi does require lots of memory.

Uncheck the ‘Anti-alias’ option. You don’t want to blur your image. Increasing the resolution is for the quality of the dots themselves. Your film is already supposed to be at a high resolution.

Click ‘OK’ and let Photo-PAINT resize your image. It’s now officially enormous.

Next, click Image→Convert to Black and White…

Select ‘Halftone’ from the drop-down box.

Select ’round’ as the shape, because there’s no ‘ellipse’ in the list. Use ‘line’ for an artistic twist.

Decide on your angle. This one is totally up to you. Lots of screen printers print at 22.5° for all films. Photo-PAINT does not allow you to set half degrees, so pick 23. You cannot make real rosette patterns (0°+x, 30°+x, 60°+x) with more than 3 films. CMYK printing cheats by putting yellow at a weird angle because yellow is the least visible. Printing with the wrong angles guarantees moiré on press which is ugly. If you print all films with the same angle, then you don’t have to think about it, but it may still not be the best way to print. When in doubt, use 23°. If you have only 3 colors, you can go ahead and put them at 15°, 45° and 75° for real rosettes. Make sure your ‘most dominant color’ is the one you’re printing at 45°, because it’s easier on the eyes.

Decide on your frequency. Make sure you select ‘inch’ from the unit drop-down. Use 50 or 60 lpi (lines/inch) if you’ve got lots of control on press and you can squeeze out small dots. Use 35 or so if you’re okay with seeing your dots but want to be sure it turns out good. Also take into account that you should not have more than 1/5th the halftone screen lpi compared to your screen mesh ruling. So if you have a 305 mesh, you can go up to 60 lpi, but if you have a 120 mesh, 35 lpi is pushing it. What will happen is that your dots are too small to hang on to the mesh and will wash out.

Click ‘OK’.

You now have a halftoned film. The resolution of this bitmap is exquisite and it’s close to the maximum resolution your printer can print. Photo-PAINT doesn’t make smooth dots, so you have to help it along.

Click Image→Convert to Grayscale because you can’t run any filters on a black and white image.

Then click Effects→Noise→Median… and enter a radius of 1 followed by ‘OK’.

Click Image→Convert to Black and White and click ‘OK’.

Save your halftoned film.

You can print this with any printer, with or without a RIP. Select Photo quality if you don’t use a RIP so it deposits enough ink.

 

GIMP halftones

GIMP is free. Get the latest version.

Open your sep.

Click Image→Duplicate to create a new image from this, so you don’t modify the original. Close the original.

Click Image→Mode→Grayscale and make it gray (it should be gray already but it doesn’t hurt to make sure).

Click Colors→Curves to adjust the curves. ScreenSeps does some dot gain compensation but this feature is (at the time of this writing) experimental and needs to be tweaked. If you have experience in screen printing, you may be able to eyeball it. Otherwise, some test prints may be necessary. When in doubt, just skip this step. Your prints should be reasonably good without any modification. Note that in order to compensate for dot gain, you should move the line up to lighten the film.

Click Image→Scale Image… Select ‘inches’ from the top drop-down box. Make sure the image size in inches is correct. Copy the width in inches to the clipboard. If the chain on any of the buttons is broken, click that button to link the width and height (aspect ratio). Then put ‘1200’ in the ‘Resolution’ fields. This changes the physical width. Therefore, paste the physical width in inches back in the top box, which will also adjust the height since the width and height are linked. At the bottom of the dialog it should display the size of the new image in megabytes. It doesn’t do this however, because this is not PhotoShop and it is also not Photo-PAINT. You can calculate it yourself, but instead you can just click ‘OK’ and hope your system does not crash. If you find your system has crashed and after restarting you are back here to try again, then you should lower the dpi to, say, 900 dpi. Make sure your new dpi is a whole multiple of your old dpi. The lower your dpi here, the less quality your dot shape will be, but high dpi does require lots of memory.

Select ‘None’ from the ‘Interpolation’ drop-down box. You don’t want to blur your image. Increasing the resolution is for the quality of the dots themselves. Your film is already supposed to be at a high resolution.

Click ‘Scale’ and let GIMP resize your image. GIMP may complain that your image is huge. Click ‘Scale’ if that happens. Your system may choke. If you make it through then your image is now officially enormous. At the bottom of your window it will display the actual size in memory but only if you move the mouse out of the window. This information is not very helpful because it’s now too late.

Next, click Filters→Distorts→Newsprint…

Decide on your frequency (output lpi). Use 50 or 60 lpi (lines/inch) if you’ve got lots of control on press and you can squeeze out small dots. Use 35 or so if you’re okay with seeing your dots but want to be sure it turns out good. Also take into account that you should not have more than 1/5th the halftone screen lpi compared to your screen mesh ruling. So if you have a 305 mesh, you can go up to 60 lpi, but if you have a 120 mesh, 35 lpi is pushing it. What will happen is that your dots are too small to hang on to the mesh and will wash out.

Decide on your angle. This one is totally up to you. Lots of screen printers print at 22.5° for all films. You cannot make real rosette patterns (0°+x, 30°+x, 60°+x) with more than 3 films. CMYK printing cheats by putting yellow at a weird angle because yellow is the least visible. Printing with the wrong angles guarantees moiré on press which is ugly. If you print all films with the same angle, then you don’t have to think about it, but it may still not be the best way to print. When in doubt, use 22.5°. If you have only 3 colors, you can go ahead and put them at 15°, 45° and 75° for real rosettes. Make sure your ‘most dominant color’ is the one you’re printing at 45°, because it’s easier on the eyes.

Select ‘PS Square (Euclidean dot)’ as the shape, because it’s awesome and there’s no ‘ellipse’ in the list. Use ‘line’ for an artistic twist.

Enter ‘2’ in the oversample box. What it does is, it smooths the dots so we don’t have to clean them later. ‘3’ is actually better, but takes more than twice as long.

Click ‘OK’.

Be patient, the oversampling makes it 4x as much work to do the halftoning and your image is huge. Your computer may choke a little at the end. That’s okay. Just be patient and wait until it is done. If you don’t wait, you may have to start over after breaking something and GIMP dies on you.

Your image is still grayscale, and it also has gray pixels (not just black and white ones) due to the oversampling.

Click Colors→Threshold. Enter ‘127’ in the left box and ‘255’ in the right box and click ‘OK’.

You now have a halftoned film. The resolution of this bitmap is exquisite and it’s close to the maximum resolution your printer can print.

GIMP cannot create real Black and White (1 bit) images. Any image can still have only black and white pixels in it, however. The image will be larger on your hard drive than an image saved with PhotoShop or Corel PHOTO-PAINT.

Save your halftoned film (click File→Export as…).

You can print this with any printer, with or without a RIP. Select Photo quality if you don’t use a RIP so it deposits enough ink.

 

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