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Scanners and Color Management:

With evolving and rapidly changing technology of digital cameras, printers, and monitors, one would expect that use of scanners would diminish over the time. Although digital cameras are the most popular devices used to capture photos, scanners are still widely used for converting media such as pictures, artwork, documents, transparencies, slides, and film negatives into an electronic format.

This section discusses calibration, characterization, and profiling of lower-end scanners. Use of ISO scanner calibration targets, handful of software applications, and "how-to's" is described. Comparisons are made for different scanner targets and software applications.

Scanners:

Scanners capture an image by measuring colors reflected from or transmitted through the image at many points and assign internal R'G'B' values to the colors at those points. In reflective mode, whenever a target is placed on the glass top of the scanner, the light from the lamp is incident on the target. This incident light is reflected by the target onto the CCD sensors in the scan-head. Finally, the R,G,B values measured by the scanner for a particular color spot on the target are function of the spectral sensitivity responses of the CCD sensors. Process is similar for reflective mode. There are three main types of scanner technology available:

Drum Scanners:

Drum scanners are mostly used by publishing industry for high quality images. They are rarely used to scan prints - high quality inexpensive flatbed scanners can do the job quite well. Film, however, is where drum scanners continue to be the tool of choice. Drum scanners from companies such as Aztek or ICG allow high resolution scanning (12,000 dpi, 16-bit/channel) of reflective and transmissive media that are mounted on an acrylic cylinder.  This so called “drum” rotates at high speed (2,000 rpm) while it moves the object being scanned in front of precision optics and a light source (quartz-halogen lamp) to deliver the image information to the highly sensitive sensors - photomultiplier tubes (PMTs).  Oil based drum mounting of transparencies dramatically improves scan quality and it is the best way to avoid dust and scratches.  These scanners have plenty of controls to affect the result by allowing adjustments focused to any specific area of the image.

Many manufacturers of scanners recently moved toward desktop drum scanners – smaller and less expensive units. A word of warning from FLAAR in case that you are looking for a cheaper drum scanner.

The obvious disadvantage of drum scanners is that they are not as portable and easy to use as flatbed scanners and take a long time to scan an image. The biggest disadvantage though is price. New low end scanners start at around $16,000 while high end scanners can cost $65,000 and above. Added to that is prices of the drums and high end scanning software.

Flatbed Scanners:

Flatbed scanners are typically composed of a glass plate, under which a cold cathode fluorescent tube (CCFL) or a xenon lamp are located which illuminate the image. The light reflected (transmitted) off a small area is passing through the lens via redirecting mirrors onto a beam splitter that decomposes the light into spectral channels. Light is then passed through the three color filters (RGB) to optical detectors, which for most of the scanners (and digital cameras) are charge-coupled devices (CCD). Mirrors, lens, splitter, filter, and CCD sensor make up the scan head. As the scan proceeds, the scan head moves slowly (accompanied by a typical scanning noise) across the whole document (one pass).

To process the image on computer, a scanner driver has to be installed, that allows communication with the scanner. Most scanners use generic TWAIN driver. This means that the application does not need to know the specific details of the scanner in order to access it directly. For example, one can acquire an image from the scanner from within Adobe Photoshop because Photoshop supports the TWAIN standard. An alternative approach is to use specific software provided by the manufacturer or by a third party suppliers (SilverFast, VueScan).

Film Scanners:

Film scanners are specifically made for direct transmissive scanning of photographic films, such as negatives and positives (slides). Film scanners usually accept uncut film strips (35mm) and scan them using a CCD sensor. The advantage of using a dedicated film scanner as opposed to a flatbed scanner is that the area to be scanned is much smaller, allowing for higher resolution scans (4,000 dpi).

Hardware Components:

Lamps:

The quality of scanner light source is essential for outcome of the scanning process. Majority of scanners today use one of the following lamps.

Sensors:

The core component of the photo-quality scanner detection system is the CCD array. The CCD, or Charge Coupled Device, is the most common type of sensor, and is usually very precise and accurate. It's also a time-tested technology: they are used in many applications, including video and digital still cameras. A CCD is an integrated-circuit chip that contains an array of metal-oxide-semiconductor (MOS) capacitors that store charge when light creates electron-hole pairs. The charge accumulates at each capacitor (pixel) and is read in a fixed time interval and corresponds to the amount of light that struck the sensor.

Scanners and Color Management:

Let's begin with a few great references that I found useful when writing these pages.

Technical Terms:

At this point there are several technical terms that deserve a brief discussion.

Density, Dynamic range, Dmax :

Density is defined as a ratio of logarithm of intensity of the incoming light to the intensity of transmitted light (log(I/I0)). For a given % of transmitted (or reflected) light T(%), the density D = - log(T/100). For example, if a film passes through 25% of the light, the density would be - log(25/100) = 0.6 D. For 0.025% of transmitted light, the density = 3.6 D.

The luminance of an image area, Y, is related to the density, D, by

Y = k * 10-D

where k is the view-box luminance in cd/m2. For example, for film density of 0.15 (second step of Stouffer transmission step wedge T4110) and view-box luminance of 100 cd/m2, the output luminance would be Y = 100*10-0.15 = 70.8 cd/m2. The corresponding CIELAB Lightness (L*) can be calculated using equations described in gamma section of these web pages.

Dynamic range (DR) is ratio of the brightest signal that can be recorded to the darkest signal that can be detected. The higher the dynamic range, the more information we get from the darkest areas of the scanned medium. For digital cameras, the dynamic range is measured in f-stops (corresponds to exposure value EV).

EV = log2(f2) - log2(T)

where log2 = logarithm base 2, f = f-number, T = shutter speed in seconds. For each stop, the light decreases by half (a factor of two in exposure). For example, for f=2.8, T=1/30 sec, EV = log2(2.82) - log2(1/30)=3-(-5) = 8. Figures are rounded. If your calculator doesn't calculate log2, you can calculate the logarithm of base 10 (log on your calculator) and multiply it by 3.32193 (the inverse of log10(2).

log2(x) = 3.32193 * log10(x) = 1/log10(2) * log10(x)

Relationship between the dynamic range and f-stops is:

DR = 3.32193 * f-stops

Read more in Dynamic range of cameras and scanners Norman Koren Imatest Documentation.

Maximum dynamic range (Dmax) is the darkest signal that can be recorded. It depends on signal encoding at the stage of analog to digital conversion (AD). In general,

D = log(2B-1) (I)

where D = reported dynamic range given in Densities, B = bit depth of A/D conversion.

Typical transparency film has minimum density (Dmin) of about 0.05 D in the clear area of the film. Then for a scanner with a Dmax of 3.6, the effective dynamic range is only 3.55 D. If a scanner had Dmax of 3.60 D, everything denser than 3.60 D would be interpreted as completely black (clipped). Dynamic range of current 8-bit LCD monitors is dictated by the video LUT encoding (8-bit), giving us D = 2.4 regardless of display contrast ratio (e.g, 500:1). Read the Gamma Encoding and Dynamic Range section in the Dynamic range discussion at photo.net.

Examples

Dmax:

To get at least a qualitative idea of Dmax values for different materials, following table summarizes the most typical values.

Upon inspection of Dmax values in Table 1, it follows that for a decent flatbed scanner, Dmax has no importance for scanning prints and film negatives. The dynamic range of scanners for reflective media is still higher than the density range of the scanned media. Thus reflective IT8 targets do not have enough maximum density suitable for measuring the dynamic range of scanners. Special targets, such as Stouffer transmission step wedge T4110 (positive film, Dmax= 4.1 D) are used for this purpose.

Measuring scanner Dynamic range and the Dmax values :

ISO 21550:2004 standard specifies methods for measuring and reporting the dynamic range of scanners. It applies to scanners for reflective and transmissive media. Some manufacturers still report the dynamic range directly from the bit depth of the implemented A/D conversion using the formula (I).

There are three common methods to determine the maximum density Dmax:

Practical use of Method 2 was described by Don Hutcheson in his excellent Scanning Guide. Gray scale step wedge, for example Stouffer T4110, is scanned (with scanner gamma correction) and opened in Photoshop. "New Levels" layer is created above the image background layer and the white point (white right-hand slider) is moved almost all the way to the left. The density at which no further separation is visible between scale steps represents the Dmax value.

Method 3 which is based on S/N ratio is the most objective method for determination of Dmax values of a scanner (this method is also used in Stepchart module of the Imatest.). The engineering definition of dynamic range is: Dmax corresponds to the maximum recordable signal (the raw value at which the sensor saturates, Dmin) divided by the read noise, which is the lowest recordable signal (Dmax).

While dynamic range should be calculated for each RGB channel separately, visually weighted average of RGB values for the grayscale patches is typically used. Relative luminance is calculated from RGB values as follows:

Y(i) = 0.2126 * R(i) + 0.7152 * G(i) + 0.0722 * B(i)

Coefficients in this equation come from the transfer matrix of sRGB color space, more specifically from the second row which is used to calculate luminance Y (eq.VII). Same relative luminance numbers would be obtained if we used the coefficients from the Adobe RGB color space (0.2974, 0.6273, 0.0753). Note that sum of these (row) coefficients corresponds to the normalized CIE-Y coordinate of the white illuminant (that is to value of 1 for all illuminants). Also note that in this case, gamma-corrected R',G'B' values are used instead of linear values.

For determination of the dynamic range and related values the test chart has to be scanned. For flatbed scanners having a film/transparency adapter, Stouffer transmission step wedge T4110 is used. The step chart T4110 is placed onto the film holder. Strips of black insulation tape are used to cover the unused areas on the film holder. A number of four scans per chart is used to minimize errors caused by temporal noise or mechanical tolerances. Depth of 16-bit per channel is used in all measurements (48-bit scans). The dynamic range is determined from the function given by the calibrated density values of the patches in the test chart (T4110) and the resulting averaged RGB values from the four scans. See the next example.

Dmax estimation for Epson Perfection 4990 Photo :

To proceed, we will need to:

Dmax -- per Method 2:

Following the Dan Hutchesons method described above, the visible separation between neighboring steps disappeared at step 36. This corresponds to Dmax of 36 * 0.1 - 0.05 = 3.55 D.

Dmax -- per method 3:

Download the Dmax Excel sheet to calculate the Dmax values from Stouffer T4110 wedge step. I prefer using the Stepchart module of Imatest.

Alternatively, use Photoshop and follow instructions in this NSTLs document. Described formulas were applied into the Dmax Excel spreadsheet (ranges N:U).

In summary, several methods were described for estimation of scanner  Dmax value -- all based on measurements of transparent Stouffer T4110 step wedge. Both simple and more elaborated methods provided Dmax = 3.60 for the Epson Perfection Photo 4990 scanner.

Scanner Calibration, Characterization, and Profiling:

Terms such as scanner calibration, characterization, and profiling are sometimes used interchangeably with profiling being the most common meaning in the context of scanners and color management. To be consistent with conventional digital photography terminology, scanner calibration as described here may differ from descriptions found in "scanner" literature.

By analogy to display devices, calibration should result in a device being in normalized, standard, and predictable state. However, in contrast to displays, scanners are always driven by a software through the manufacturer specific software drivers. Thus it may be sometimes difficult to set scanner to a desired and defined state. Sufficiently calibrated state is often achieved by turning off (in software or driver) any features that adjust black and white points, compensate for color cast, white balance, or somehow automatically adjust the image appearance. Sharpening feature should be also turned off to ensure reproducible results. Use of Digital ICE and GEM (grain enhancement) technologies was shown to have no impact on color appearance.

Scanner characterization is process of finding a mapping function between scanner RGB values and device independent color space such as CIELAB. The transform is typically built by using a mathematical technique such as the least squares algorithm employing both the reference data and measured data. Since mapping is inherently nonlinear, polynomial functions are frequently used assuming that the source and destination spaces are correlated by a set of polynomial equations.

Profiling is extension of the characterization process which results in scanner profile. To generate the profile, software is used to describe the device's full color range capabilities. The gamut of the device is determined by measuring the RGB values for a set of known color patches. Measured data is then used to generate input profile for the device. Profiles are then applied to an image in order to calculate RGB values for a defined color space. Typical scanner profiling process involves scanning a reference target that has numerous color patches. IT8 and HTC are examples of such reference standards. Software is used to compare the color reference values that accompany the target with the measured values. Profiling and characterization do not change the behavior of the scanner (same as for monitors).

Analysis of Tone Response Curves (TRC) :

First step in characterization of a calibrated scanner is to measure its tone response curve. The TRC describes relationship between the raw RGB input values and the resulting luminance or lightness values. When using a calibration target (e.g., IT8, HCT) each patch has been measured using spectrophotometer and its CIEXYZ values are reported in the corresponding calibration target file. To construct TRC, we plot the raw RGB values (input) against reported luminance values (CIE-Y). Both RGB and Y-values are typically normalized in a range from 0 to 1. If grayscale patches are used (GS0-GS23 of IT8.7 target, column B27:V27 of HCT target) performance of each of RGB channel can be assessed. Moreover, scanner gamma can be calculated by methods mentioned in display gamma section and certainly by using the log-log(gamma) formula.

Figure 3: Grayscale patches of Velvia RVP 50 IT8 target

Typical TRC curves and analysis is shown in Figures 3-5. In this example, IT8.7/1 transmission target made by Wolf Faust for Fuji Velvia RVP 50 slide film (V3) is described. Figure 3, top panel shows per channel response curves by plotting normalized raw RGB values against luminance values (CIE-Y) as reported in the target calibration file. Only the grayscale portion of the scanned IT8 target is plotted (GS0-GS23). Shape of all three curves suggests a gamma value embedded in the raw RGB values. Greater contrast in blue and green channels is also apparent. When luminance is converted to LAB lightness (L*), curves get more of a linear shape, although a slight convex shape is still visible (middle panel). Bottom panel shows the same dependence for lightness of the corresponding grayscale image (RGB values are averaged). Another distinct feature of this plot is clipping of shadows below RGB of approx. 10.

To calculate gamma at which the scan was performed or to optimize the gamma for linear response, both RGB- and Y-values have to be transformed into log domain (Figure 4, top panel). This transformation assumes that gamma embedded in the TRC follows a power function. Slope of the fitted line then provides the value of gamma. In this example, fit to a varying number of points was employed, specifically to 6, 8, 10, 12, 14, and 16 data points counting from the top right (highlights). The bottom panel shows relationship between the number of fitted data points (red circles) and "goodness" of fit as judged by the adjusted R-squared statistics (blue stars). The highest values for adjusted R^2 correspond to number of fitted points between 6-12. Slopes (and gammas) of the fitted lines for this range show values of 2.51-2.52.

Figure 4: Log-Log(gamma) fit

Figure 5: Grayscale LAB profile

Indeed this scan was done in Nikon V(ED) scanner with gamma set to 2.50 in the Nikon Scan 4.03 software.

The last example of scanner characterization is shown in Figure 5. CIELAB components for grayscale patches of IT8.7/1 target are plotted as a*, b* vs. L*. These values are directly available from the target reference file. As numbers suggest, the grayscale has a slight green-bluish tone along the most of the tonal range, except for the maximum white which suggests a slight magenta tint. This is consistent with Velvia characteristics - greenish tone and magenta tint in highlights.

To adjust scanner’s tone response curve, you can alter it by adjusting the tone controls and/or internal gamma value.

Scanner profiling:

As discussed in sections on display calibration/profiling, it is of the utmost importance to have a control over all the device variables that can affect its color performance. With scanners, while light source and internal optics are controlled quite well, it is the software that is the major source of performance inconsistency. As Bruce Fraser eloquently put it: "the key to successful scanner profiling lies in setting up the scanner software correctly, then keeping it set that way". In technical terms, scanner profiling aims to ensure that raw RGB values captured by the scanner are consistently translated into standard color space such as CIELAB or CIEXYZ. Rules for such translation come from "calibrating" the raw input data to experimental data recorded in scanner target (e.g. IT8). In other words, the RGB signals acquired from a scanner (raw RGB) are related to a spectral or colorimetric representation (read patches in scanning target) through the process of scanner profiling. Typical approaches create a scanner profile by scanning a target containing a set of color patches. The target is simultaneously measured with a color measurement device to obtain spectral or colorimetric measurements in CIELAB color system. The scanned RGB and the corresponding colorimetric data are related via a 3D transform (RGB) such as a 3x3 matrix, polynomial, LUT, etc. The process of calibration must generally be repeated for each input medium, i.e., combination of substrate, colorants, and image characteristic colors.

Now, few links to providers / re-sellers of IT8 and HCT targets.

While software packages such as Vuescan and SilverFast have their own calibration modules, I'll start with BasICColor Input module to get some profiles created (see the following movie). Profiling using AryllCMS is described in the corresponding section.

Results of scanner profiling and profile evaluation :

Before we get into analysis of scanner profiles, a word of caution is in order. As discussed by Bruce Fraser, Chris Murphy, and Fred Bunting in their book Real World Color Management (2nd edition, p. 227), the following tests will not provide us with some unambiguous benchmarks of profile quality, profiling packages, or targets. Instead, these comparisons will give us a reasonable feel of the relative accuracy of profiles and targets used to create these profiles.

1. Objective tests - obtaining CIEDE2000 color differences:

First examples include data generated from a simple comparison of Lab values predicted by the profile (A) and LAB values reported in the profiling target reference files (B). We will use the scanner target (IT8.7/2, HCT, ..) to profile scanner and then use the scanned values of the very same target (for which LAB values are known) to validate the profile. To get data (A), scan the physical reference target and save resulting scan as tiff file. Reference file (B) is usually provided by the target manufacturer. It is the text file which can often be downloaded from the web or just measured by spectrophotometer (e.g., EyeOne-Pro). There are several tools to perform such comparison.

First (and free) method uses Argyll CMS icclu and scanin modules. To record and retrieve raw RGB values of scanned IT8.7/2 target we start Argyll CMS by typing the following command string:

>scanin -v o data\g190_IT8.tif data\It8.cht data\R050302W.txt

The resulting file will be named g190_IT8.val and it will contain RGB values of the scanned target patches. In this case, we are interested only in these RGB values, that is, in the raw RGB values as captured by the scanner. This file can be renamed to g190_IT8.txt and opened directly in the ColorThinkPro or PatchTool (Gamut Tools) applications.

To obtain predicted LAB values, use the following command:

 >icclu -v -ff -ia -pl -s 255 data\scanner.icm < data\RGBin.txt > data\RGB2Lab.out

Resulting text file RGB2Lab.out will contain the corresponding LAB values. Open this file in Excel and extract the LAB values. Paste them (all 288) into this Excel sheet to generate the LOGO formatted output file *_lab.txt (cells C9:E296).

Now, having both the generated LAB file (*_lab.txt) and the reference target file available, open the Profile Maker 5 Measure Tool and launch the Calculating module. Open both files in the appropriate windows and inspect the color differences.

Second option for comparing predicted and reference LAB data is to use the Imatest Studio and its Multicharts module. A wide variety of views and metrics is available to evaluate scanned images. One limitation to be aware of is that Imatest uses just a handful of standard RGB color spaces and cannot evaluate HCT targets. With that in mind, I follow these steps to prepare my scanned images for analysis:

Now, make sure that the target reference file used for scanner profiling is available and launch Imatest application.

Following flash movie illustrates the steps for image evaluation.

Obtaining raw RGB values from IT8.7 target as captured by scanner use of Multicharts:

If raw RGB values of a scanned image embedded in tiff file are needed, here is an easy way to obtain them.

Another tool fully capable of providing comparison of predicted and reference state for scanner targets is the Patch Tool application and its integrated module – Gamut Tools. 
To obtain Lab values predicted by the scanner profile, we will need the file containing RGB values in the scanner color space. There are two options to obtain these values (as discussed above) – Argyll CMS scanin module or the Imatest-Multicharts.
Once the file with RGB values is obtained, we open it in the PatchTool application and assign the scanner profile using the Gamut Tools.

Here is how:flash, patchtool

ColorThink Pro software provides basic as well as detailed reports and visualization. As in the previous examples a file containing raw RGB values, scanner profile, and reference LAB values are needed (download examples here). For a step-by-step description, review the following movie.

Results of the color difference comparison can be conveniently viewed in CIE (xy)-chromaticity or CIELAB systems.

2. Subjective Tests:

 

 

These tests are based on:

• Visual evaluation of two synthetic images, namely the Granger rainbow and Don Hutcheson RGBEXPLORER8.
• Visual evaluation of real scanned reflective images – after scanner profile was assigned to them.

The main purpose of the first test is to get any hints as to the limitations of scanner profiles assigned to these synthetic images. We are looking for regions of sudden changes in hue or saturation that may manifest themselves in real scanned images. These deficiencies are then verified in the second test.

HOW TO measure:

For all subjective evaluations, the ColorThink Pro software was used (Photoshop can be used instead). Note that results of these tests depend on quality of your display and its gamut size.

Synthetic images: After opening the synthetic image in CTP, scanner profile was assigned to embedded RGB values and results were compared with the same image having a large "ideal" input profile assigned to it (DonRGB4.icm, Ekta Space PS 5, J. Holmes.icc). Areas of hue/saturation shift or channel clipping were recorded.

Real scanned photos (reflective media): Four scanned landscape photos were used for evaluation. Eizo CG19 monitor was calibrated before these tests. After opening these images in CTP, scanner profiles were assigned to embedded RGB values. Areas of unusual hue/saturation shifts or channel clipping were recorded and the corresponding colors inspected for similar shifts in the real scanned images. Differences between profiles thus can be directly observed.

35 mm slides (transmissive media): 3-5 scanned landscape slides were used for evaluation. Eizo CG19 monitor was calibrated before these tests. After opening these images in CTP, scanner profiles were assigned to embedded RGB values. Areas of unusual hue/saturation shifts or channel clipping were recorded and the corresponding colors inspected for similar shifts in the real scanned images. Differences between profiles thus can be directly observed.

Required files:  RGBEXPLORER8.tif, DonRGB4.icm, Ekta Space PS 5.icc (Joseph Holmes), Granger rainbow.tif (988 KB)

Step-by-step description of image evaluation is in the following movie.

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2.1. Results for reflective media

Table 8. Epson Perfection 4990Color profiles, SF gamma 1.9, CTP, Results of subjective image evaluation

ICC/ICM Profile	Profile characteristics
	Profile name	Cast/Tint in Lights	Lightness	Contrast	Defects
IT8 SF-Studio AI6.6	SF66-4990_g190.icm	neutral	lower	lower	dark blues
IT8 – i1 Match3	SF4990_g190_GM_IT8.icc	yellowish-greenish	normal
ST1.4 – i1 Match3	SF4990_g190_GM_14.icc	magenta	normal
HCT – i1 Match3	SF4990_g190_GM_HTC.icc	yellow-green	normal		dark brown; yellow band in grayscale
IT8 -Argyll LUT	SF4990_g190_ARG_LUTqm_IT8.icm	yellowish	normal		cyan bleached skies
HCT- Argyll LUT	SF4990_g190_ARG_LUTqm_HTC.icm	greenish	normal		cyan bleached skies
IT8 -  BasICColor	SF4990_g190_IT8_bas.icc	neu., magenta in lights	normal	higher	red, yellow
HCT -  BasICColor	SF4990_g190_HCT_bas.icc	magenta		lower	red, yellow

 

Summary (subjective analysis - prints):

1. As one would expect, no single profile is perfect. Both synthetic and real images reveal slight casts in highlights and sometimes deficiencies in color areas. Most frequently, it is the blue-magenta region and saturated greens in real images and dark blue/magenta areas in synthetic image.
2. Profile performance of reflective media depends on the paper finish and brightness (glossy, matte). If a bright image is scanned, profile adjustment may be needed to make the scan look darker.
3. Use of any of the above described profiles depends on the image scene (Table 8). Set white and black points in Levels with eyedropper, neutralizing any cast in whitest and blackest areas.
4. A little bit of additional color editing in Photoshop is always necessary.
5. IT8 target and profiles made in SF-Studio Ai6.6 worked best with the neutral grayscales. At the same time, scans appeared a little muddy and darker for color images. However, images further edited in Photoshop turned out quite well.
6. IT8-based BasICColor profiles were better for skin tones than HCT-based ones. However, saturated red and yellow colors were more washed out in BasICColor profiles when compared to IT8-based SF-Studio Ai6.6 profiles.
7. There was no apparent difference between profiles made from scanned targets coming from SF Studio or VueScan applications. Only profiles made at the same gamma (2.2) should be compared.
8. As far as profiling software is concerned, I could not get a handle on i1 Match3 application. While IT8-based profile worked fine, HCT and ST1.4 profiles has defects in dark brown hues (grainy) and highlights (magenta tint), respectively. My preferred profiling applications for reflective media are BasICColor Input and SF-Studio Ai6.6. For some images featuring red rocks, however, i1 match IT8 targets worked just fine.
9. For most images, IT8 calibration resulted in same or even slightly better colors than HCT calibration. On the other hand, HCT-based calibration (BasICColor) worked better for red rocks of the US southwest.
10. From a practical point of view, from now on I use profiles coming from BasICColor Input and SF-Studio Ai6.6 applications. The former is used for both IT8 and HCT profiles, the latter for IT8 profiles only. Scans are done at gamma 1.90 and "lightness adjusted" profiles are made for both IT8 and HCT targets. To darken final images (if needed), I increase lightness of the scanned targets using Curves (114->139). This way the final profile creation is tricked and lightness is lowered.

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2.2. Results for transmissive media

Table 9. Nikon Coolscan V ED Color profiles, SF gamma 2.5, SF Studio Ai 6.6

Slide film type and Target used for calibration		Profiling Software and subjective evaluation
Slide Film Type	Target	SF Studio Ai6.6	i1 Match3	Argyll CMS LUT	BasICColor	Notes
Elitea	IT8-Ekta	M tint	slight M tint	M tint in skies	M tint	No image darkening after profile assigned.
Elite	HCT-Velvia50		M tint	OK		i1 still shows a slight M tint, Argyll has better colors. Correct in PS - autolevels.
Provia/Sensiab	IT8			general landscape, _extD	large body of water, _extD	Needs extended profiles (too dark images) or profiles made at lower gamma (2.2). IT8-Velvia target works just as nice.
Provia/Sensia	HCT-Velvia50		snow	general landscape	large body of water	BasICColor: Y-ish
Kodachromec	IT8	dull colors, dark img	OK for "heavy" cyan Kodachrome tint	OK for "light" cyan Kodachrome tint	OK for "heavy/light" cyan Kodachrome tint	i1 and Argyll may show clipping in blue skies, experiment with BasICColor, i1, and Argyll
Velviad	IT8	dull colors, dark img	red rocks, _extD	general landscape; large body of water, _extD	Y-ish	Often needs extended profiles (too dark images) or profiles made at lower gamma (2.2).
Velvia	HCT-Velvia50		general landscape	general landscape; red rocks	large body of water, _extD	better color and details in water; skies better than IT8

a) Ektachrome Elite II50, b) Provia 100, Sensia II 100, c) Kodachrome 64 d) Velvia RVP50 (rated 40):

HCT: HutchColor Velvia Target HCT01F35T; IT8: IT8.7/1-1993 target from Wolf Faust (www.coloraid.de) Kodak Ektachrome, Fujichrome velvia RVP50, Fujichrome Provia, Sensia, Astia; IT8 SF: LaserSoft Imaging Kodachrome Target

M: magenta; Y: yellow; B: blue; +++ subjective appearance rating

In some cases, profiles created at scanner gamma 2.50 darkened the scanned images a bit upon profile assignment. To remedy this issue, I used method described by Don Hutcheson in his Scanning guide, namely Extended-Range Profiles (p. 25). Open a scan of test image used to create the profile (*.tiff) and adjust curves (ctrl+M) or levels (Ctrl+L) at the darker side (make them even darker). In my examples, I changed the levels input from level 0 to output 12 (image in Photoshop darkened even more). Then save modified tiff file and generate the profile again (name it *_extD.icc). Assign it to a scanned image. There is nearly no decrease in brightness after assigning the profile. Alternatively, the same effect can be achieved by assigning a profile created by scanning target at lower gamma (2.2-2.4) to an image scanned at higher gamma (2.5).

Note on use of SilverFast Kodachrome IT8 target (purchased directly from SilverFast) with BasICColor input profiling software. Since the original reference file supplied with Kodachrome transparent IT8 target does not match the grid in BasICColor application, copy the reference file in C:\Program Files\SilverFast Application\SilverFast NikonM\SilverFast\IT8 Reference Files\LaserSoft Imaging\Transparent\E090311.txt and remove rows A-H 20, 21, 22 (total of 24 rows). Then place this new created file in C:\Program Files\basICColor Software\basICColor input 3.1\references\transmissive\Kodak\K3-Data Kodachrome 35mm folder.

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Summary (subjective analysis - slides):

1. Profiling Provia and Sensia slides resulted in profiles that darkened the image after profile assignment. Use of extended profiles is thus recommended. Argyll CMS worked well for general landscape images while BasICColor gave better profiles for images of rivers and sea water.

2. Creating scanner profiles for Kodachrome 64 slides call for use of multiple software packages. To my surprise, I had a very little luck with the SilverFast Studio Ai 6.6 profiling module (SF provides the IT8 target and supports native profiling). On the other hand, BasICColor Input application worked quite well for any Kodachrome slide. i1 Match and Argyll CMS gave good results for a "heavy" tinted and "lightly" tinted Kodachrome slides, respectively. Watch for burned out skies. By heaviness, I mean the strength of the typical cyan tint of Kodachrome slides.

3. Profiling Ektachrome Elite 50 scans using Ektachrome targets worked reasonably well with Argyll CMS modules. Use of HCT target is preferred, even though a slight magenta tint is still apparent. Image then still needs a color correction in Photoshop.

4. Successful profiling for typical Velvia RVP50 slide film calls for use of multiple software applications. i1 Match-based extended profiles are great for typical USA southwest red rocks when IT8 target is used. However, if HCT target is used for profiling, Argyll CMS gave slightly better results. For a larger body of water (rivers, sea), BasiCColor/HCT combination worked very well. For more details, see comments in the last two rows in Table 9.

5. In general, HCT-based profiles provided better visual appearance than IT8-based profiles. Colors were usually more rich and more details were recovered. I found using the HCT Velvia 50 target suitable for creating profiles for other slide types.

All scanner profiles mentioned in Tables 9 (Nikon CoolsScan V ED) are available for download here (1.5 Mb). Since they were created for this particular scanner and a specific slide type, they are unlikely to give you good results for other scanner and slide type. Try and see.

Scanning Workflows

VueScan 8.5

Vuescan is a very powerful scanning program and the only scanning product that works under multiple operating systems (Windows, Mac OS, and Linux).  It has all the necessary functions for a "raw" scanning – no extra image editing functions.  VueScan comes in two versions: the Standard version and the Professional Edition.  Both versions support about 1,200 flatbed and film scanners by accessing the scanner hardware directly at low level (no drivers are needed).  In addition to the Standard version options, the Professional Edition can generate RAW files and supports ICC profiles and IT8 profile generation. RAW data have no image correction done to the captured data and thus are suitable for archiving. VueScan also supports some special tasks, such as batch scanning, auto-focus, infrared channel for dust and scratch suppression, and multi-scan to reduce scanner noise. RAW files are supported in 64-bit format (48-bits for color and 16-bits for infrared channel). Files can be saved in special TIFF format or as Adobe open source DNG format. TIFF RAW files can then be opened in VueScan while DNG file can be opened either in VueScan or Photoshop.

More details are either at the author’s web site or at “Scanning tips site”.
There are several workflows to choose from depending on your specific task.  Ini files are available for download to assist you with selection of proper settings.  Just place those files into c:/Vuescan directory, use File -> Load Options to load the settings into VueScan and modify source/destination pathways for your files/profiles (change anything shown as "abc" and C:\temp).
Following descriptions assume that targets, images, or slides were placed on the glass plate or in the film holder.

Download example of IT8_profiling.ini file

ICC profile is created and saved to the directory assigned in Color: Scanner ICC profile (in Windows  it is C:\WINDOWS\system32\spool\drivers\color) (B). VueScan creates simple matrix-based profiles. Reference file that comes with your IT8 target is required.

Using these settings, scanned image is assigned the scanner icc profile and converted to destination (working) color space during the scan. I prefer setting Color -> Color Balance option to “None”. That way the black and white points are not used to correct the white balance, thus not expanding the image tonal range.

Download example of Scan_2RAW_64RGBI_dng.ini file

Images of scanner targets created from these settings can be used for scanner profiling in other applications (Eye-One Match 3, Profile Maker, Silver fast DCPro, Argyll CMS, …). Generated tiff files have encoded gamma of 2.0-2.1, the RAW file is linear (gamma = 1) with embedded infrared channel for later dust cleaning. RAW files can be opened in VueScan and processed through the Infrared clean (software analogy to ICE). For details, see the next paragraph.

Download example of Process_from_RAW_64RGBI_dng.ini file

Download example of Process_from_RAW_64RGBI_dng_2tif_gam_lin.ini file

SilverFast Studio Ai:

SilverFast Studio is a member of SilverFast (SF) family of scanning programs from LaserSoft Imaging.  Many scanners and modes are supported by a variety of SilverFast modules although quite restrictive licensing policy can quickly become cost prohibitive. The main features differentiating SilverFast Ai from other scanning programs are extensive image editing capabilities and complete color management. There is essentially no need to use Photoshop afterwards.
Since many instructive and descriptive tutorials exist on the Web, I will list those that I used to learn about this software.

For setting the optimum gamma value, see Ian Lyons Optimising the Scanner Response. In case of Epson perfection 4990 Photo, my optimized gamma setting was 1.90 with the following RGB values of grayscale patches: GS0 230, GS11 113, and GS23 27.

See the changes in levels as gamma values change.

Later in Photoshop.

Following these steps, an image is scanned into the scanner color space (internal, device dependent RGB values). Scanner profile is assigned to the image in Photoshop and the image is then converted to a standard color space, such as Adobe 98. Same results can be obtained following a shorter sequence of steps in the next paragraph.

Using these settings, the image is assigned the scanner icc profile and converted to destination (working) color space during the scan. Image can be directly edited in Photoshop.

Images of scanner targets created from these settings can be used for scanner profiling in other applications (Eye-One Match 3, Profile Maker, Silver fast DCPro, Argyll CMS). RAW files do not have embedded infrared channel.

Nikon Scan 4:

Nikon Scan software is included in the Nikon scanner package. The following movie shows the typical workflow when making scanner profiles. Important step is to deactivate the color management function when creating profiles. Later on, this feature should still stay disabled to ensure consistent results. I prefer using tiff format to capture RAW data. Another important features enabled in V (ED) series is Multi Sampling and Digital ICE, both of which ensure higher quality of scans. Set ICE to "Normal" to avoid "excessive" cleaning of the scanned material. To speed up scanning process, disable Digital ICE in Preview (it will be applied only to final scans). Settings for nearly all menus can be saved and loaded next time when you run the same workflow.

Argyll CMS:

Scanner profiling is described in Argyll CMS section.

Typical scanner workflow: Don Hutcheson

Joseph Holmes’ scanner workflow: Chrome Space 100

Links and References: