## Linearizing the Base Gray Ink Curve ### Printing the linearization target The initial quad curve created in the custom curve creation screen had an initial correction applied when you created it, but you need to create a final linearized curve based on measurements from a printed step target. #### Target Sizes The grayscale linearization can accommodate target sizes from 11 to 256 patches from a wide range of measurement devices and file formats. I generally recommend a 128-step target if using an i1 pro device in strip mode, but linearization will work fine with a 21-step target if using a flatbed scanner or manual measurement device to read the target. - Open PrintTool and open the image. - Make sure there is no color management, and then select Run Print. - Open the QuadToneRIP print dialog options (remember to press the Layout button to open the menu to access the QuadToneRIP settings). - Set the mode to 16-bit to enable the Curves 1, 2, and 3 menus - Select the menu for Curve 1 and choose the newly-created base gray curve. - Set the printer settings to highest resolution (2880x2880) Unidirectional and Installed Black. - Leave the advanced options unchecked. - Then run the print. ### Measuring the target There are too many devices and software to detail in these instructions, but the general rule is to measure from light to dark and save the lab values as a plain .txt file. Please see the [[0. Measurement Device Workflows|measurement workflows]] section detailed instructions and videos for the most popular devices. ### Loading the Measurement Data Press the button to load the measurement data from the target you printed a measured. The software will automatically detect the data format, and if there are multiple samples per patch, average them into a single set of values and show a graph of the measured values in the measurements chart and list on the left side of the Linearization screen. #### Measurement Data Graph  There are four sets of data graphed when loading the measurement data. - The black dots are the original interpolated measurement data. - The software interpolates the original measurements into 256 steps, but there are only 129 steps graphed in the chart. These dots will not change when adjusting the smoothing sliders. However, they will change if you edit the values in the table on the left - The red line represents the 256-smoothed values and will change when adjusting the two smoothing sliders or when updating any of the values in the original measurement data list. These are the values used in the linearization calculations - The straight black line is the linear L\*a\*b\* values from Dmin (top left of the graph) to Dmax (bottom right). The black line is a reference for the linear output, but those values **are not used** in the actual correction calculations. - The Green line shows the target L\*a\*b\* L\* values and **are the actual values used** in the linearization calculations. You can adjust the output values to be something other than perfectly linear output with the manual curve control panel. ### Smoothing the Measurement Data Proper smoothing of the measurement data is one of the more critical adjustments you will need to make. Thankfully, it is all visual and you don’t need to do any calculations on your part. There are two sliders that control the number of points used in the smoothing algorithm. The main smoothing value adjusts for any large bumps in the measurement data but can distort it at the extreme highlight and shadow ends of the tonal scale. Use the second smoothing slider to adjust the values from the main smoothing slider back to the general trend in the original measurement data while also smoothing out any remaining bumps in the curve. The goal is to use enough smoothing to remove any bumps or flat spots that will result in banding in the final print and remain true to the general trend of the original data. #### Main Smoothing Window Size: The number of points to use will depend on the size of the measurement target. 21-step targets will require less smoothing than 128 or 256 step targets. A larger value will result in a larger moving-average window and a smoother curve. Very high values will distort the shadow values because the window will include and average values from the 3/4 tones. A good starting point is a setting of 11-35. (Note: the window size will always be rounded up to an odd number to ensure that there is an equal number of input points around the point being smoothed. #### Fine Smoothing Percentage: A value of 0 will turn off the smoothing, and start to apply the smoothing as soon as you begin to adjust it to the right. A higher value will result in a smoother curve but will distort the highlight and shadow values if it is set too high. For those interested, here is what is happening in the smoothing steps: The main smoothing slider is a simple moving average. It creates a window of the specified number of points, averages them into a new value, then moves down one step and repeats until it creates a new set of 256 smoothed values. Those values are input into the second smoothing calculation, where the fine smoothing slider value determines the percentage of points to use in a smooth-step interpolation to recreate the final 256 smoothed values. Those final values are graphed as the red line and used in the actual linearization calculations. ### Manual Curve Control ![[Grayscale Linearization Screen with Standard Manual Curve Settings.png]] The manual curve control allows you to adjust the final print densities to something other than a perfectly linear L\*a\*b\* L\* line. The main purpose of this control is to adjust for how prints on matte papers can appear too light or low contrast compared to the display have shadow values that appear much lighter than the image on the display. It adjusts the output values in the .quad curves to appear more perceptually correct and removes the need to use a 2nd adjustment curve to the digital image prior to printing the negative. #### Standard Perceptual Rendering Curve Setting You can also choose the standard compression button to apply a curve that is similar to the kind of compression you get with an ICC profile. The software will automatically determine which curve to apply based on the Dmax. If the Dmax is lighter than an L`*` value of 10, it will apply a shadow correction curve. If the Dmax is darker than an L`*` value of 10, it will apply a slight curve to lighten the quarter and mid tones and linear shadow values. ##### Matte Black Measurements with Perceptual Rendering ![[Pasted image 20230823141957.png|Matte Ink Perceptual Rendering]] ##### Gloss Black Measurements with Perceptual Rendering ![[Pasted image 20230823142441.png|Gloss Perceptual Rendering]] ### Saving the linearized .quad curves When you are happy with the smoothing and manual output curve (if used) and have added any notes, you will need to save the linearized .quad file to the Quadxxxx folder for your printer. If you are going to blend with the SCTV corrected color ink channels to create toning curve components, save the initial linearized gray curve as a .qtpc file. This will allow you to easily load the measurements and linearized quad values in the Quad Blending tools to preview the color of the blend. #### Naming the Linearized Curve I always suggest using the same name as the non-linearized curve and adding -LIN before the .quad extension. If I use the manual output curve, I add -LIN-MC, -LIN-CS, or LIN-PR (for “manual curve”, “compressed shadows”, "perceptual rendering"). You will also need to rerun the install command for the printer (found in Applications/QuadToneRIP/Profiles/Your-Printer) so that it is available in the QTR print dialog options. You can also export the linearized gray curve as a .qtpc file that will contain the corrected quad values and the corrected output LAB values. These files can be open in the Quad Curve Blending module to preview the approximate blended color, or for adding the gray ink component in the QTP Profile Creation module. ### Confirming Linearization To ensure the new linearized curve is printing correctly and make the .qtp file, you need to make a test print of your standard test image and include a bullseye gradient that will show any obvious reversals or problems with the linearization. Include a simple 21-step grayscale target with your test print to measure, confirm linearity, and add the measurements to the .qtp file from the QTP Profile Creation module. The other important factor to check is the smoothness of the mid-tones. The grayscale torture test image in the resources folder includes two bullseye gradients as well as linear gradients broken up into 11, 21, 51, 101, and 256 steps. Use this image along with your standard test image to make sure there is no posterization or banding in the final linearized curves. Open the PrintTool and arrange your test image, the torture test, and a 21-step target so that they print together and that there is enough space around the 21-step target for easily reading the patch values. Also, be sure to check that color management is still turned off in the main Print Tool window. Open the QTR print dialog windows by choosing the Print and Paper Settings, going straight to the Print button, and choosing the new linearized gray curve in the Curve 1 drop-down menu. [[Creating the .QTP File]]