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Calibration for DAC Images, Phase 1

Viewers wishing to adjust their monitors to render images from the first direct capture phase of the DAC Digital Imaging Initiative more accurately may be interested in these process control images. Although we are now producing images with different equipment and processing procedures than those documented below, this page will remain online for reference in conjunction with certain heavily used images to which it is relevant. Chief among these are images of Goya's 80 Caprichos. Viewers making sustained or serious study of those images may find the information below to be helpful. If a link from an image page led you here, this information pertains to the image on that page.

Although the Kodak color patches represented here are manufactured for other uses, they work fairly well for representing successive stages of our baseline image processing, and suffice for approximate monitor calibration for those images. If you're familiar with how color bars should look (or if you have a colorimeter), a monitor set to render image number 3 accurately should do well at representing certain JPEG images from the DAC Collection (bearing in mind the note below regarding low-end grayscale reproduction).

The images below may appear to be more broadly useful than they actually are. They are not reliable tools for monitor calibration in absolute terms. The baseline corrections that they illustrate were derived roughly from RGB values sampled with PhotoShop's eyedropper tool. These values were compared to those of analogous areas in Adobe calibration images intended for quite different purposes relating to printed output. This workaround--the best we could do at the time without colorimetric equipment--yielded images whose utility is distinctly limited to relative calibration in regard to similarly prepared JPEGs.

These progressive JPEG images were exported from Adobe PhotoShop 4.01 in the same manner as images from the collection, using HVS JPEG 2.20 with our standard settings: Q of 84, optimized Q Table, no pre-filtering.

1. Almost-raw capture file with sharpening (Unsharp Mask at 60%, radius 0.6 pixels, threshold 12 levels)
2. As in (1) above, but with subsequent color correction (blue channel adjustment +3, +4, +6, saturation adjustment +20)
3. As in (2) above, but with subsequent contrast expansion (in this case, the tonal curve applied to most Goya Caprichos)
	The curve applied to image (2) to produce image (3). Each image was treated with a curve of this general contour, based on a visual assessment of its legible rendering onscreen. While a curve of this sort renders the gray scale's four densest patches undifferentiable on many monitors, it worked well with many images of prints by suggesting their tonal richness. Generally all images from a series of prints by one artist (e.g., the Caprichos) were treated with one curve to support comparative viewing.

Interpretation Notes

www.wesleyan.edu/dac/ddii/calibrate1.html
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