YRGBK 3 – Color density and saturation

Getting the right amount of color density and saturation in a separation is one of the most important and challenging issues when reproducing an image in print. YRGBK 3 provides several options for adjusting the output of colors, and getting them working together makes all the difference.

Before running a separation it is important to set Photoshops dot gain preview to match your intended output. See the YRGBK quick start guide for more information.

There are actually four adjustments that can be made that will affect the color levels in a print when running YRGBK 3. Each adjustment plays a specific role, though the effects appear to overlap. In this tutorial I will discuss each setting and how it is used to calibrate an image for a particular print setup.

Color Density and Saturation Sliders

In the Settings tab there are two sliders which adjust the colors: Density and Saturation. in addition there is a checkbox labeled Auto.

• The Auto checkbox, which I will cover in a later tutorial, actually overrides all the color adjustments , so for now just leaving it unchecked is what we need.

• The Density Slider provides a global setting for all color density. This setting provides a Levels adjustment that is applied to all the color channels equally, and is used to increase the the values of the darkest pixels in the channel.

• The Saturation slider is also a global adjustment for all colors and is used to adjust the mid-tone values of each color channel. This can be used to adjust for dot gain or to compensate for changes made to the color density.

The two sliders can be used together to increase the amount of color printed in the most colorful areas of an image, while maintaining the proper amount of color in the mid-tones. Start by increasing the Density until the brightest colors are fully saturated, then reduce the saturation to bring the mid values back in line. This is helpful when printing graphics with bold, solid colors or when printing on textiles.

 For Screen printing it is helpful to set your channels darkest values to as close to 100% as the ink color will allow. This is especially true when reproducing art with solid areas of color. Using the Density and saturation sliders in this way allows adjustments to be made quickly and to be customized for each image.

Color Levels and Balance

In the Color tab there are sliders for adjusting each color individually, as well as a slider labeled Balance. These provide nearly the same function as the Density and Saturation sliders in the settings dialog but are better suited to calibrating the script overall rather then for a particular image.

• The Color Levels sliders adjust the density of each color channel individually. This can be helpful if a separation setting is generating too much or too little of a particular color. Adjustments made in the settings tab are added to the changes made in the color levels.

• The Balance slider adjusts the mid range values of the levels adjustment, similar to the saturation slider in the settings tab. This is helpful  with images which require greater control over middle color values and can be used to adjust for dot gain or for increased color levels settings.

In practice I will use the settings tabs Density and Saturation sliders for adjusting separations on the fly, while making adjustments to the color levels and Balance if I am creating a new color setting profile. Occasionally an image will need more or less of a particular color, often the Yellow, so I will use the Color levels to improve the separation.

Conclusion

These four sliders provide a lot of control over the output of a color separation but can have a profound effect over the results. The default settings have been carefully calibrated over a large range of images and are a good place to start. Making small, measured changes is the best approach. A change of 10% to 20% is often more then enough to produce the desired results. Remembering how the settings interact is also helpful when making adjustments to the color channels. In the video below I demonstrate the color adjustments made to create the poster separation settings used on the homepage video.

I hope you find this tutorial useful and feel free to contact me if you have any questions.

YRGBK 2.3 – The Gray Component

In a CMYK separation Cyan, Magenta and Yellow are often combined to create the Gray values and tones in an image.  When using Gray Component Replacement (GCR), in a CMYK separation, The amount of Black that prints into these areas can be adjusted by changing the GCR amount.

When separating an image using the YRGBK script, all of the Gray values and tones are handled by the Black, Gray or Gray Component channels. The color channels only contain Hue and Saturation information for the image, and are not blended to create gray or tones.

• Gray values and tones that would be printed using CMY, in a CMYK color separation, are put on the Gray Component Channel by checking the Gray Component check box.

When the Gray Component check box is selected, a second dialog will be presented with the Gray Component Ramp setting. This slider determines the amount of black that is moved to the Gray component channel. Values added to the Gray component are removed from the Black channel.

• A higher setting increases the amount of Gray Component, and decreases the amount of Black.

The Gray Component channel in YRGBK 2.3 can be treated like  a light black channel, and can be printed using an extended, or transparent Black ink. Splitting the black in this manner offers several advantages. This includes the ability to use a transparent ink, a harder squeegee, and a lighter touch on the light black channel, while allowing for good saturation and contrast provided by an opaque ink and a heavier impression with the regular Black.

• Splitting the blacks provides some flexibility in the printing of an image, although it does add an extra screen to the process. Unchecking the Gray and Gray component check boxes puts all the value information on the Black channel.

Gray values are removed from both the Black and the Gray Component when the Gray check box is selected. The Gray Slider determines how far the Gray prints into the colors, with higher values increasing the amount of Gray printing into the colors themselves.

With the Gray check box selected, a second dialog containing the Gray Ramp slider will be presented. The Gray Ramp slider determines the value of the gray, with higher numbers generating a darker gray, and removing pixels from both the Black and the Gray component.

• The Gray slider Combined with the Gray Ramp settings determine the balance between the Gray, Black and the Gray component. The Gray Slider determines the amount of gray in the colors, and the Gray Ramps determine the values.

The Gray Component channel provides a useful option for printing photo realistic images and any color separation which would benefit from greater control over the values in an image. The Black channel which is created by checking the Gray component option is the same Black that would be created when generating a CMYK color separation. With the Gray and Gray component options Unchecked, this information is retained in the Black channel, providing the full range of values in a single channel.

YRGBK 2.3 – Shadow and Highlight color

The shadow color and highlight color options are designed to be used to increase the amount of colorprinting under the Black and White, respectively. These adjustments are limited to the darkest and lightest areas of the image, and only modify the color channels.

Increasing the color printing in the shadows helps to make a richer print with better dynamic range, and allows us to use a lighter touch and a sharper squeegee when printing the Black. In some cases, if there are light areas of color that need a bump, increasing the color printing in the highlights can help.

Generally, I have found it is helpful to bump up the colors in the shadows. This allows for more colorful shadows and deeper blacks. Highlight areas rarely require a boost to the color. If an image is mostly light or pastel colors, however, this option may be helpful.

Setting the Black point and White point

The Black point is the Darkest set of pixels in an image, while the White point is the Brightest. By setting the darkest and lightest pixels to 100% Black and White, respectively, we can increase the tonal range as well as the contrast in an RGB image. This step also ensures that any solid areas of Black or White are set to print with 100% coverage. Increasing the tonal range and contrast in the RGB mode will always improve the results from the YRGBK script.

Levels or Curves
There are several ways to approach setting the Black points, but for the most part in Adobe Photoshop we can use either Levels or Curves. Both tools can do the trick, but for the most control over the results I always go for the Curves. In Photoshop’s menu go to:

Image/Adjustments/Levels
or:
Image/Adjustments/Curves

A histogram is a graphic representation of the pixels in an image. The Levels dialog is a Histogram with sliders, where the left side represents the dark values and the right side is the light values. The number of pixels in a value range is represented by a line going up from the bottom, so the taller the line in the graph the more pixels in that range. The Arrow on the left sets the Black point, while the arrow on the right sets the White point. The Curves dialog can also display a Histogram if you check the Histogram checkbox.

In this tutorial I am actually going to describe two techniques for setting the Black and White points in Adobe Photoshop’s RGB mode. Which approach you use depends on the image and your goals. The best place to start is by converting an image to Adobe RGB, if it is not already.

Edit / Convert to Profile..
Destination Profile : AdobeRGB (1998)

In both the Levels and curves dialogs, there are three eyedropper icons on the right or along the bottom; the left one sets the black point, the right one sets the white point, while the middle dropper sets the neutrals.

• Double click on the Black eyedropper to open its color dialog. Set the color to 100% Black. Do the same for the White, setting the value to 100%.

Now, when you select an eye dropper and click on the image, that value will be set to 100% White or Black.

• Select the Black eyedropper, click on the darkest area in the image to set it to Black. Do the same with the White eyedropper, setting the lightest areas to white.

The Middle dropper can be used to set the neutral values in an image. This can be helpful with photographs taken with the wrong lighting settings, or if you have a gray card in the image. This dropper can cause a large color shift in the image, and is not needed to set the Black and White.

The Dropper approach is good for photographs, especially if they lack contrast or had poor lighting. It can also be a quick way to set a Black or White point on simple separation.

The Droppers may cause a noticeable shift in color, and in some cases we just want the light and dark areas adjusted. We can manually set the points using the Curves dialog, while keeping the middle values in place, to avoid color shifts.

Open the Curves dialog:
In the curves dialog we can also set the Black point by moving the 100% point on the curve to the darkest pixels in the image.

• Start by setting the Show Amount to Pigment/Ink %
• Check the Histogram check box.
• Click and drag the 100% point to the first set of pixels in the histogram. Do the same for the 0% point to set the white.

If you click and hold on the image with the curves dialog open, you will get a reading in the dialog showing the original and new values. This can be used to measure the values in the image. If you Cmnd click in the image, or click along the curve line, you can set a point on the curve.

To avoid making color shifts we can break this adjustment into two steps and set values along the curve.

Open the curves dialog:
• Set points along the curve by clicking in the image or along the curve line. Set points below 50%.
• Slide the 100% point to the darkest pixels in the histogram. This value can be determined by measuring in the image.
• Adjust the curve if needed for a good tone transition.

Click OK and repeat the process for the White. This time setting points above 50% and moving the 0% point to the right.

This is a good approach when we need to set the Black and white, but do not want to shift the colors in an image. It also gives good control over the resulting value transition. In this example it shows in the white where it fades into an off white shade, and I could soften my curve to smooth that transition out.

We can also look at the Black point of each channel in a color separation to be sure they have good contrast and range. The techniques are the same as above, with a single color channel selected.

Color channels generated by the YRGBK script have their black points set based on the saturation and brightness of the ink colors. We can customize these colors by changing the black point of a channel, and adjusting the channels ink color to match.

It is also helpful to adjust the Black point when a channels darkest values hover over 90%. We can shift the value to 100%, while setting points on the curve, and improve both the coverage and range of the color.

Finally, the white point of a color channel should be inspected to avoid random dots and 1% areas, which can be a problem when making screens.

Setting the Black and White points is a crucial step that is often overlooked. Ensuring good value ranges and solids in an image from the start will always improve the results.

The Color Separation Workflow

Preparing a color separation for screen printing can be an involved process. We can break the process into several distinct stages, however, to make a manageable color separation workflow. I cover each step in some detail here on this site, but for this post I want to tie them all together. While each stage can have it’s own series of steps, here I will outline the main parts, while including links to detailed explanations.

• Preparing the image –  File preparation
This first step is easy to overlook, but careful attention at this stage can make the entire process easier while improving the results dramatically.
There are three main parts to this step:
1. Setting the images Black and White points
2. Cleaning up the image
3. Removing the background

• Creating a Base Separation – The YRGBK Script
Although many color separators will jump right in and start building a color separation from the prepared image, I have found it is helpful to start with a base separation generated using a standard process. There are several advantages I find with this approach.

First, a decent color separation algorithm can get you a good ways down the road towards a finished product, while a great one can get you pretty close to the finish line, depending on your needs. Elements like a Base white, HIghlight White and Black channels can be created consistently from project to project, while color channels can be generated in a way that ensures all color information is present.

Finally, it can be helpful to leverage the knowledge of an experienced color separator when using an scripted algorithm or technique for this process. The YRGBK Script was developed for this purpose.

• Customizing the Separation.
The best results are obtained when a color separation is designed to accommodate not only the image, but also the printing technique and substrate it is being printed on. Whether it is splitting solid colors from halftones for textile printing, or converting primary colors to Custom colors for color matching and ink coverage, the results are always worth the effort.

• Clean up and review.
Once the separation is complete it is good to have a review process and clean up stage. I like to make this a defined part of the process so I do not get bogged down in clean up while I am trying to customize a separation. It is also helpful to ensure the image has been cleaned up and to take a final look at how the colors are going to print. Stray 1% dots, 98% solids that should be 100%, and misplaced custom colors can all be handled easily at this point, while providing potential headaches if they make it on to the press.

• Convert the gray values to printable dots – SimRip 3
Since a color separation is generated using gray values in our channels, it is necessary to convert these values to printable dots which can be imaged on the screen or plate. Dot Size,  Shape and Angle all play a part in not only the look and feel of the print but also in the quality of the result.

Whether I am printing to the Direct to Screen printer at the shop, or making film in my art studio, I have found significant benefits to handling this conversion within Adobe Photoshop. Even though I may be printing to an actual Rip, which traditionally handles this step, the flexibility and control as well as the ability to carefully review the output has led me to converting every job to halftones within Adobe Photoshop.

• Output the Color separation to film, plates or screens.
Finally, with the separation complete and converted to halftones, the channels are sent to the printer.

YRGBK2.3 – Saturation and Color Density

The saturation and color density sliders in the YRGBK script can be used to adjust the amount of color in your final separation. Although both adjustments appear to have a similar effect, the results of each are very different and they can be used together.

Color Density
The color density slider adjusts the Black point, or how dark the darkest pixels will be, for all color channels. Each color channels black point can be set individually using the Custom Colors dialog, while the Color Density slider adjusts all the channels together.

The Black point of the color channel determines the amount of ink being printed overall, and is balanced with the color of the ink itself. If we are using a duller, less saturated ink we can increase the density of the channels to compensate. If our inks are pure primary colors we can decrease the density levels. With the Color Density setting set to 0, the black point for all channels is set entirely by the custom color sliders.

Auto
 The Auto check box automatically sets the darkest pixels to black in each color channel. This setting overrides the values applied in the Custom Colors dialog, so the results can be unbalanced if the image does not contain a full set of primary colors. The Auto setting is useful, however, if you intend on customizing your colors. The Color Density slider increases the Auto amount for all color channels.

Saturation
The Saturation slider applies to the mid range values in a channel. The Darkest pixels in a channel are not made any darker, but the amount of ink overall is adjusted. The default setting is 50, which means that pixels in the 50% range will be set to 50%, or no adjustment.

Dynamic Range and Coverage.
Dynamic range is the difference between the lightest and darkest values on a channel or in an image. A print with good dynamic range will have high contrast and be able to reproduce the full range of values in an image.
Coverage is how well an ink deposit covers the substrate. For screen printing on textiles it is nice to have an ink printing at 100% coverage where the color is brightest. Most printers will try to achieve a solid print in areas covered by a single color. If the channel itself is coming in below 100%, the print pressure will be increased to create a good ink surface. The resulting dot gain from increasing the print pressure will reduce the dynamic range.
We can anticipate this by setting the solid areas on a color channel to 100%, allowing for complete coverage while maintaining the range of values the color can reproduce. This is only possible where a color in the image is a pure primary, or we are using a custom ink color.

How is this used?
The saturation and color density adjustments can be used together to fine tune the output from the YRGBK script.

If our inks are dull or our image brightly colored, it can help to increase the density of the colors. Pushing the darkest values closer to 100% increases the dynamic range of each channel, increasing the range of colors that can be achieved.

If the separation itself is too dull or too colorful overall it can be helpful to adjust the Saturation slider. Since this adjustment does not affect the black point the dynamic range and maximum density of the colors are not changed.

Finally, if we are planning on using custom colors, the Auto setting can be used with the density slider to quickly set the black point for all channels so the densest areas of color are printing at 100%. In this case the Saturation slider value can actually be reduced in order to maintain the mid range.

Yrgbk 2.3 – The Custom Black, White and Gray sliders

In the YRGBK 2.3 script, the Black, White and Gray sliders control the amount of Black, White and Gray ink printing into the colors. The effect is to brighten the image by letting the colors show through. The level of brightness is controlled by the sliders; higher values in the slider increase the amount of ink, while lower numbers decrease the ink levels. Controlling the amount of Black in an image’s colors is useful for images that are either brightly colored or contain a lot of detail.

The Saturation Mask

The adjustment applies only areas of color. The Script generates a mask using the saturation values in the image. The greater the intensity of the colors, the heavier the Saturation Mask will be. Detailed adjustments can be made in the Custom Black dialog, using the Saturation Mask settings, by checking the Custom Black Checkbox.

Using the Black, white and gray sliders

if I need more detail in my colors, or if my colors are highly saturated, I can increase the value in the slider. if I need less, say for instance I have an image with pure solid colors and a black line, I can decrease the black slider to clear the black out of the colors.

The default settings are balanced with the colors assigned to the color channels.

YRGBK 2.3 – Use Ink Colors

The Use Ink colors option does just what it sounds like, sets the final channel colors to printable ink color values. By unchecking the Use Ink Colors check box we can display a wider gamut of colors, but they will be outside our printable color range.

The Script

The YRGBK script splits the colors in an image into Hues and the Values, with all of the Value information going to the Black, White and Gray channels. The Hues are then split into a set of primary colors, and, if the Use Ink Colors box is checked, assigned printable ink colors. The Black channel is adjusted automatically to work with the colors.

Color Gamut

When a color in an image falls outside of the color range generated by a color model the color is said to be “Out of Gamut”. The YRGBK script generates a color model whose Gamut is limited by the ink colors used. Colors which can not be created by the inks are printed using the closest color available. By Unchecking the Use Ink Colors check box we can keep the colors in their original, primary state, generating a separation with a much larger color range.

If, when running a separation through the script you notice a large color shift, it can be helpful to turn Use Ink Colors Off to visualize the whole color gamut.

To generate a Primary color separation:
• Uncheck the Use Ink Colors checkbox in the main window
• Check the Custom Black box
• Check the Custom Colors box

Adjust the Black Values

In addition to setting the color values, the YRGBK script makes adjustments to the Black channel to accommodate the brightness of the ink colors. When Unchecking the Use Ink Colors option, there will not be enough Black generated to render the image fully using the default settings. To fix this:

• Set the custom Black slider in the main window to 100.
• In the secondary Black Generator window, set both the Midtone and Shadow values to 0.

Adjust the Saturation Levels

Color channels are also adjusted for Saturation levels by the script. The Colors in the primary set have a saturation of 100%. Ink colors, on the other hand, have much lower saturation values based on the selected inks.

For most images the default settings are calibrated to generate good results using the Ink colors. For some images we need to adjust the density of the channels to achieve proper saturation levels. The Color levels sliders in the Color Generator dialog adjusts each channels density individually. To reset the color adjustments for a primary color separation:

• In the Main window, set the Color Density to 0
• In the secondary Color Generator window, set all the color sliders to 0, the Midtone to 100, and uncheck the Transition Mask box.

Conclusion

The Use Ink Colors option is checked by default, and in most cases this is where you will want to leave it. This setting will automatically bring your colors into a printable range that works with the default settings in the rest of the script. Often it is easier to customize the color channels after running the script then it is to run a primary color separation and make it printable. A primary color separation generated in this way would need to be manually adjusted to achieve printable results.

That said, in the case where you have large color shifts, unchecking the Use Ink Color dialog can quickly create a wide gamut, fully saturated color separation. Creating a primary color separation in this way can help to visualize a solution, or can be used as a starting point for working the separation up manually.