Section 5.4. Raster Image Processors (RIPs)

5.3. CM and Scanning: In Depth

Many of you will do just fine with the scanning information presented in the previous chapters, but here we will go into much greater detail for those of you who need (or just want) it.

First, remember that the general rule of thumb is that the better the original image or scan, the better the quality of the output.

If you understand how to calibrate and profile a scanner, you are most of the way toward doing the same with a digital camera.

In this example, I will use the Epson Scan software with a Perfection 3200 scanner. Most other software works in a similar fashion; if you understand the concepts here, then you should be able to adapt them to your particular scanner. (Note that there are a few scanners, including the entire HP line, which are designed for the beginner or business user, which do not give you the controls to create a high-quality scan.)

So let's dig right in and set up the scanner. By default, the scanning software is in Full Auto Mode. There are a variety of options that are available if you go into the Customize options, including the type of original, the resolution of the desired output, dust removal and color restoration, and a few other features. Next to the Scan button (and not very obvious in our example) is the File Save Setting button, which allows you to select the location, file format, and name of your file.

The Home Mode is the next mode on the list, and it is a bit more advanced. Home Mode gives you considerably more options, including the Document Type that you are scanning. You are also asked for the Destination Document Type and the Output Resolution. The Configuration button at the bottom of the window brings us to a new window.

Finally, we are getting to the good color stuff. From the Configuration screen, click on the Color button, and you are presented with three options. Under the first option, Color Control, uncheck "Continuous auto exposure." If you leave this option on, the scanning software will take the lightest tone and make it pure white and take the darkest tone and make it pure black, which is a problem because we'll lose all the details in the highlights and shadows. Set the Display Gamma to the gamma that you have your monitor calibrated and profiled to.

The next option in the Configuration window is ColorSync on the Mac and ICM on the PC. This option allows you to apply a scanner profile to the scan and then convert it directly to your working space or, if you are not planning on editing the image at all, to apply the printer profile. For the most part, I would not use this setting, even though it looks cool, because it doesn't allow you to calibrate the scanner.

Last but not least, the third option is the No Color Correction option. This option would be used if you were planning either to apply your scanner profile or color correct your image in a program such as Photoshop. To obtain the best-quality scan with this option, it is best to scan at a high bit level.

Professional Mode is the third and most powerful scanning mode for the Epson Scan software. This is the mode where we're going spend the most amount of time, going through the many controls and options. As with the two previous scanning modes, we first need to determine whether we are working with reflective or transparent media. To scan transparent media, such as film, you either need a dedicated film scanner or a flatbed scanner that has a separate light source for the film.

In Professional Mode, we have an even greater number of options for Destination /Image Type. The two that we are most concerned with here are 48-bit Color and 16-bit Gray Scale. Earlier in the book, we spoke about the advantages of working with files with a higher bit depth. The concept of 48-bit color is a bit confusing until you realize that a 48-bit image contains three 16-bit files: one each for red, green, and blue (hence, 16 x 3 = 48-bit). Unless you are doing high production scanning with minimal to no corrections or enhancements in image-editing software such as Photoshop, you should scan at the high bit level, which will allow you to have the most tonal information with which to edit. After editing, you can convert the image into an 8-bit file.

The Adjustments give you a variety of options in the Reflective Mode, such as Unsharp Mask Filter and Descreening Filter. If we change over to the Film Mode, new options become available, including Grain Reduction, Color Restoration, and Dust Removal. Since our main concern is achieving the best color from the scanner, we won't go into detail about these options. If you need to find out more, see the Appendix for a list of books and manuals that cover some of options more thoroughly than we can here.

Our foremost concern is the Adjustments indicated by the four icons at the top of the window. In order to make these options available, you need to be in Color Control Configuration. If they are grayed out, then you have selected either the ColorSync or No Color Correction options.

The leftmost icon is for Auto Exposure, which we don't want to use because, as mentioned earlier in this chapter, it blows out the highlights and plugs the shadows. The second icon from the left is the Histogram Adjustment, which is where we will do the most work in calibrating the scanner. We'll also be using the next two buttons in part: Tone Correction and Image Adjustment.

A great tool that we can use to assist us in calibrating the scanner for reflective originals is the GretagMacbeth ColorChecker. This target has been around for many years, and the reason that it works so well is that there are a limited number of patches (compared to other targets), and it is easy to find out what the RGB values of the patches are.

The values in this chart are for the Adobe RGB (1998) color space because most photographers will use it as their default color space. By reading the RGB values of the ColorChecker in the scanning software and adjusting them to those in the Adobe RGB chart, we can calibrate the scanner.

The Histogram Adjustment window gives you a tremendous amount of control over the scanner. We will use this window to set the highlight, shadow, overall tonality, and overall color balance using the ColorChecker. A histogram is a representation of the number of pixels at any given point on the tonal scale. Black is on the left, while white is on the right. The value of black is 0, while white is 255. For our individual RGB channels, 0 is no color, while 255 is the pure color.

If you work in other color spaces, a great resource of values for other color spaces can be found at Click on the Calc button and then on "ColorChecker RGB Summaries, Spreadsheets and Lab TIFF File." For those of you who have color geek tendencies, there is a lot of other cool information on this site.

In the Histogram Adjustment window underneath the histogram, you will find a series of sliders for both input and output. The Input scale has white, gray, and black sliders; three eyedroppers for white, gray, and black; and a numerical readout for each. The output scale is much simpler, with only white and black sliders and readouts. By using these tools, you can go a long way toward calibrating your scanner.

Let's go step by step:

  1. Read the RGB values of the white patch of the ColorChecker. You'll notice that R is 248, G is 245, and B is 237.

  2. Read the RGB values for the black patch of the ColorChecker (R = 35, G = 38, and B = 36).

  3. Read the RGB values of the medium light-gray patch (R = 138, G = 142, and B = 138).

  4. Compare the values obtained from steps 1 and 2 to values in the Adobe RGB (1998) chart. Our white values are high, our black values are low, and our gray values are low. This indicates that, by default, the scanner is contrasty and dark. However, notice that the RGB values are relatively close to one another, which indicates that the scanner is fairly neutral. Over the years, I've worked with some scanners that were much worse than this and that had all sorts of color-balance problems. Overall, scanning software has gotten much better in recent years and is less of a battle to calibrate.

  5. Since the target is dark overall, let's move the middle slider to the left until the RGB values of the medium light-gray patch are close to the desired 159 of the ColorChecker chart. Don't worry if the values aren't exact. Two or three points make it close enough. Also, the numbers at the bottom of the screen may jump around a bit, but try to find an average value.

  6. The next point to adjust is the white value to around 242. You'll notice the values on the ColorChecker are not equal to each other, which is because the material used to make this patch was not totally neutral. The blue value sits 5 to 6 points lower than the red and green. To make this adjustment, we should move the white slider on the output a little to the left.

  7. The black point needs to be adjusted next. The desired value is 54, and in this case, no adjustment is necessary because we have the right numbers. Usually, this doesn't happen; in most cases, you will probably need to make an adjustment.

  8. Next, we need to go back and check our medium light-gray patch again because it may have been affected by the other adjustments that we just made. You can see the values have shifted a little bit, so we need to move the gray input slider a little further to the left until the values are close to the desired 159.

  9. Because our values are so close, we do not need to do any further adjustment. To make sure that you use the same calibration for future reflective scans, you should now save your settings. Saving your work will allow you to use it again. Unfortunately, the Epson software just gives us the name "Setting" and puts a sequential number behind it. Some other scanning software allows you to save these settings with a more descriptive name.

Practical Color Management. Eddie Tapp on Digital Photography
Practical Color Management: Eddie Tapp on Digital Photography
ISBN: 0596527683
EAN: 2147483647
Year: 2006
Pages: 61

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