LIMITACIÓN DEL TRATAMIENTO DE SOPORTE VITAL (LTSV)

I prefer to scan in 16-bit mode. I’ve found that the ideal way to produce scans and extract maximum formation from the original photograph is to optimize the Curves and Levels settings in the scanner software and do a 16-bit scan. I usually do this because ultimately it saves me work time. Truth be told, in 16-bit mode I can be rather sloppy about the Levels and Curves in the scanner settings, just not so much that I’m likely to lose any data

by overdoing it. I can scan batches of photographs in 16-bit mode using similar scanner settings with less trial and error and fewer repeated scans that otherwise eat up considerable time. None of the scans will be perfect when done this way, but with 16 bits of tonal depth to play with, there’s plenty of data for me to fi x everything in the computer.

Figures 4-17 through 4-19 show how fl exible 16-bit data is. The left-hand photograph ( Figure 4-17 ) and histograms ( Figure 4-18 ) come from a straight scan of a snapshot with no corrections. Because the photograph is so faded, less than half the range of tonal values is actually used; the spikes at the right side of the histograms are just from the white paper border. I crudely corrected the range of tones and colors with the Curves settings shown in Figure 4-19 to get the much better-looking photograph on the right side of Figure 4-17 .

These are very extreme corrections! Even so, the histograms on the right side of Figure 4-18 show that I did not get the dreaded “ picket fence ” effect that is so obvious in Figure 4-7 . I have a well-populated histogram that will produce good continuous-tone quality in the fi nished restoration. I would never recommend accepting a scan this bad, even in 16-bit mode. It demonstrates, though, the considerable robustness of a 16-bit scan.

You may fi nd that a practical limitation on doing 16-bit scans will be the power of your computer. It’s not merely that computations take twice as

Fig. 4-16 Channel Mixer combines the original RGB channels to make a grayscale image when Monochrome is checked. I combined 150% of red with – 50% of blue, which subtracted some of the damage because the damage was much stronger in the blue channel than the red.

Fig. 4-18 The histogram on the left belongs to the left-hand photograph in Figure 4-17 . There is only a narrow range of tones in each color channel in the scan. (The big spike in each histogram channel at the right corresponds to the “ white ” paper border.) The histogram on the right shows what the tones look like after applying the curves in Figure 4-19 , producing Figure 4-17 , right. Notice that there is no “ picket-fence ” effect with gaps in the histogram, as we saw in Figure 4-7 .

Fig. 4-17 The fi gure on the left shows the original photograph, captured as a 16-bit scan, with no effort made to correct the tonal color during scanning. This is an accurate representation of the original photograph. On the right is the same scan after I crudely corrected the color using the curves in Figure 4-19 . Having 16 bits of data per color channel makes it possible to do extreme corrections like this and still get a photograph of good quality.

long. I pointed out in Chapter 2, page 30 , that an 8 10-inch print scanned at 600 ppi in 16-bit mode produces a 175- MB fi le. Start adding layers to that in Photoshop or working with multiple generations in Picture

Window and in short order you’re swapping scratch fi les to disk. Your performance crashes dramatically. It’s something to keep in mind when you’re deciding on your scan depth. It may seem that scanning in 8-bit mode and consequently having to really fi ne-tune your scanner settings will slow down your work, but that’s not going to be the case if doing a 16-bit scan means that your image processing program goes running to the hard drive every time you perform an operation on the fi le. Back when I only had 512 MB or 1 GB of RAM in my computer, I did my best to avoid working on 16-bit fi les unless the originals were quite small.

Sometimes 16-bit data is going to be a must. When the condition of the original is so uneven that no overall set of corrections in scanning is going to produce good results, you’ll need those extra bits. The severely degraded glass plate in Figure 4-20 is almost entirely bleached out, and the scanned density isn’t anything close to even. Until you manipulate the fi le into a uniform-looking image, you’d need to work in 16 bits so that you could do different strong corrections on different parts of the scan and still have well-fi lled histograms of data.

If your computer really isn’t up to working on 16-bit fi les for the whole restoration process, I recommend a compromise: Do your scans and as much of the gross color and tone correction as you can in 16-bit mode. Then convert the fi le to 8-bit mode. That will minimize the image-quality problems of working with 8-bit fi les. Don’t worry about doing damage repair and cleaning up dust, scratches, and cracks before you convert. You can do that work as invisibly in 8-bit mode as in 16-bit mode.

The closer you get to the fi nished restoration, the less having 16-bit data will matter. When you get to the output stage, 16-bit color may not make any difference. Most printer drivers don’t take advantage of 16-bit data, although that’s gradually changing. Photoshop and TIFF fi le formats preserve 16-bit data, but JPEG

Fig. 4-19 These are the curves I used to correct Figure 4-17 . The contrast change in each channel is extreme, expanding the tonal range by a factor of two to three. This would have produced visible image degradation in an 8-bit scan; a 16-bit scan has enough extra data to handle it.

doesn’t. If your client wants the fi nished image in JPEG form, you will be sending them 8-bit color, no matter what you were working on in the computer.