Perfect Inkjet Positives without the need of Aquatint screen, rosin or spray
Adjust Curves and Levels for High Resolution Image Positives in Photoshop and Photoshop Elements No Curves, No problem!
Expose and Etch your Image with Puretch Photopolymer Etch Resist

This lesson will show you how to determine what level to adjust your blacks to so you don't need to add an aquatint screen exposure or powdered aquatint before etching. All inkjet printers lay down dots differently so this test lets you know what is ideal for your particular printer. The reduction of the black builds in a white dot that eliminates the need for an initial aquatint step. This also helps preserve detail on the highlight end. These highlight details can be burned out with a separate aquatint screen exposure, spray or rosin and also results in splotchy transitions in the light areas.

Test Exposure Times with or without the Stouffer

Ideally, you should test for the exposure time with a Stouffer step guide before proceeding here, shooting for a #6 as the target exposure for fine halftones. If you have multiple exposures that yield a #6, use the shorter time.

Test without a Stouffer: Print out a swatch of 5 and 10% gray or a horizontal swatch with a vertical light gray gradient. Use this for varied exposure times. Etch this plate for about 5 minutes (ferric) and strip the emulsion. Print it on the press, examine with a loupe and use the longest exposure that yields an etch of all the dots.

Print, Etch and Print the Grayscale at Right

1. Download the grayscale at right, print it out onto transparency selecting black ink only or Grayscale and print at the same resolution you plan to make all your positives. Don't make any adjustments, changes to the DPI or Image Mode. You may reduce it in size if necessary. Print the positive from the same software that you normally use for printing image transparencies. Select the highest quality you can for Grayscale printing. Select Premium Photo Glossy paper or similar as the media. If you have the option, choose 720 DPI (see Gutenprint). If you don't have that option, that's what it will probably print at anyway since you are only using one ink. Expose, develop and etch this image for as long as you would etch a fine halftone or similar aquatint. You may stage it out to test more than one etching time.

2. Print this plate on your press, just like you will with any finished plate. If you plan to strip the emulsion for a finished image, then strip it before printing so you will get similar contrast.

3. Analyze the print for the darkest swatch or step that prints solid black without undercutting. This is your target curve or level adjustment for adjusting grayscale images for making your transparency. The target step for black in your final print will probably be somewhere between 75 and 90% black. See third image on the right. The image was lightened slightly to show the difference between 75% and 80%. 75% printed as a nice solid black while 80% began to undercut.

Adjusting Curves in Photoshop

1. Import an image into Photoshop, change the mode to Grayscale, Image>Mode>Grayscale

2. Make any corrections, adjustments, size changes, etc. 360 DPI is recommended for inkjet printers.

3. Download the Gray Step Strip at the right and paste it along the edge of your working image. It has the same grays as the larger version. Flatten the image. Layer>Flatten Image You will use the eyedropper in this step strip later for controlled analysis.

4. Click on the Eyedropper tool, open the Info Window in the pallettes.

5. Open up the curves dialog. Image>Adjust>Curves Slide the right side of the bar down to make the Output % the same as the target % in your test print. This is the step that printed as black from your etched plate. As you adjust the curves, use the eyedropper tool to check all the black areas of your image and the Step Strip to see that they match the target %. You can see the percentage in the Info Window Pallette next to K. The first # is the original percentage with the second # being the new percentage, for example: K : 100/85%

In other words, the black swatch in the new file, once adjusted, should now match the target swatch in the original grayscale that printed black in the final print off the press.

6. Print this adjusted image out onto transparency exactly how you printed the grayscale test. Inspect it directly against a white sheet of paper, the finished print will be a little darker than what you see here. If it looks good, expose with Puretch and etch for the same time and manner as your test. You should get similar results in the blacks as your test print. If not, then make necessary adjustments.

Tip: Once you have the hang of this and what each value etches like and you begin working on images, you may want to experiment with adjusting the mid-tones to make them lighter or darker in the curves function, drag the center of the line vertically in the box. Check and un-check the preview to compare the images. After the first etch, just before the blacks begin to undercut, you can now add an aquatint to further etch certain areas to increase the tonal range.

Adjusting Levels in Photoshop Elements

Photoshop Elements does not have a curves adjustment (until recently and only very limited behavior for RGB mode) but I have figured out a work-around with the Levels adjustment for adjusting Grayscales. The result is the same as above and the lighter shadows, especially the lightest ones, do not change much which keeps the detail intact on the highlight end. These highlight details can be burned out with an initial aquatint screen exposure, spray or rosin.

First download and print, etch and print the grayscale at top right, Instructions above. The grayscale is a custom image created in Photoshop and the gray percentages are accurate as stated. It doesn't matter that they can't be analyzed the same in PSE as PS, it just matters that you are consistent in your tests with it. Just use this image as a constant benchmark for your adjustments.

1. Import an image into Photoshop Elements, change the mode to Grayscale, Image>Mode>Grayscale

2. Make any corrections, adjustments, size changes, etc. 360 DPI is recommended for inkjet printers.

3. Download the Gray Step Strip at the right and paste it along the edge of your working image. It has the same grays as the larger version. Flatten the image. Layer>Flatten Image You will use the eyedropper in this step strip later for controlled analysis.

4. Click on the Eyedropper tool, open the Info Window in the pallettes. Click on the Window Menu to find it if it's not open.

5. Use the eyedropper tool and hold it over the ideal target gray step. This is the step that printed as black from your etched plate. Take a look at the Info Window and make note of what the numbers are beside the RGB, all 3 numbers should be the same but the two sets of RGB numbers will be different (not sure why but it doesn't matter) just make a note of the RGB numbers* on the left set.

6. Open up the Levels Dialog Enhance>Adjust Lighting>Levels Slide the left pointer in the Output adjustment while checking your black areas of the image and Step Strip with the eyedropper. Continue to make adjustments with the slider until the RGB numbers in the black areas and swatch match the RGB numbers in your target gray swatch*. The first number next to the R, G and B represent the original percentage with the second number being the new level.
For example:
R : 0 / 33 (0 / zero is solid black)
G : 0 / 33
B : 0 / 33 (33 will match the 85% gray swatch in the original file)

In other words, the black swatch in the new file, once adjusted, should now match the target swatch in the original grayscale that printed black in the final print off the press.

7. Print this adjusted image out onto transparency exactly how you printed the grayscale test. Inspect it directly against a white sheet of paper, the finished print will be a little darker than what you see here. If it looks good, expose with Puretch and etch for the same time and manner as your test. You should get similar results in the blacks as your test print. If not, then make necessary adjustments.

Tip: Once you have the hang of this and what each value etches like and you begin working on images, you may want to experiment with adjusting the mid-tones in the levels function. Slide the middle pointer in the Input Levels slightly to the right to make them darker, left to make them lighter, check and un-check the preview to compare the images and use the eyedropper to analyze the new values. After the first etch, just before the blacks begin to undercut, you can now add an aquatint to further etch certain areas to increase the tonal range.

©2010 Cape Fear Press

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