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Image Fidelity

IT8.7 Profiling Tests — Continued

This is a continuation of the "IT8.7 Profiling Tests" article — click here to go to the start of the article, which describes details of the setup and how the profiles were made.
You may also need to read about profiles and relative/absolute rendering intents of white points.

[Stockholm December 2004]

Comparisons of results for a portrait

The portrait

The portrait I will show as an example, is a well exposed Fuji Sensia 100 slide, scanned at 4000 ppi with SilverFast Ai version 6.2.3r6, so the total size is about 5700x3700 pixels. At 48 bits per pixel, the tiff image is about 130 MB — too much to show here, so I show a downsampled version of 600x900 pixels. There is no sharpening whatsoever involved in the chain.

This image is chosen because flesh tones are usually good for color balance testing. It has everything from white details to dark shadows. Also, I was originally very disappointed with the quality SilverFast Ai achieved with this image, and this image was important to me.

Except where explicitly stated, the image has been given no adjustments at all since the original slide is very well balanced in all respects, so a good profile should really need much adjustments!

Settings

The setting in SilverFast called '48 Bit Color' is used when you want SilverFast to handle color management, and, if you like, other manipulations. The setting in SilverFast called '48 Bit HDR Color' is the setting used when you want as "raw" unmanipulated results as possible, usually at gamma 1.0 and usually with no embedded color profile.

Comparison methods

Most images need some tweaking, and as has been shown for a problematic image, the more you need to tweak your images, the better profile you need. This image is well balanced, so we expect a good profile to relieve us of the "tweaking bog", making it easy to do just some mild adjustments. But as will be shown below, even mild enhancements, such as simply hitting the Auto Levels in Photoshop, can have an adverse effect, where profile imperfections get amplified. Also shown is the fact that the order in which you convert to a color space and do the Auto Levels is important!

Web adaptation

Just prior to saving these images in a web friendly format, all of them have been converted to the sRGB profile, using relative colorimetric rendering intent, and the profile is embedded in the images. The conversion engine is Adobe (ACE), but tests confirm that the difference between this engine and e.g Apple CMM is very small. Then they are converted to 8 bits/channel and jpg-compressed with quality setting 'High' (8) in Photoshop. Downsampling to small thumbnail versions is done in 16 bit mode.

The fact that they are in 8 bits/channel sRGB and jpg-compressed might have you suspicious, but I can assure you that the difference in visual appearance these conversions cause, as seen on a really good monitor, is actually very small. However, your browser may or may not understand the sRGB profile that is embedded in the images, so to be on the really safe side, you need to download the images to disk and view them in your icc-aware image application. Tests on a Mac OS X system shows, however, that the appearance of these images in Safari (1.2.4) is precisely the same as the appearance in Adobe Photoshop!


SilverFast Ai 6 managed
portrait
Click to see a a larger version in a separate window (80 kB).
This image is scanned in SilverFast Ai at gamma 2.0 with the setting '48 Bit Color', and it is color managed by SilverFast using a profile created by SilverFast, which converts the image to the standard working space Adobe RGB (1998).

Not totally off, but it is too dark and the flesh tones sure look much too red — but she has not been lying too long in the sun! The real slide shows very neutral colors, although one can see that it is an afternoon light.

To correct for darkness and somewhat off colors, it is common to adjust Levels in Photoshop — images that are reasnoably normal can often be improved by simply doing Auto Levels in Photoshop. This is illustrated in the next image:

SilverFast Ai 6 managed, Auto Levels
portrait
Click to see a larger version in a separate window (96 kB).
The previous image with Auto Levels applied in Photoshop. (Note that this is done while we are still in the standard working space Adobe RGB (1998).)

This actually made the whole thing worse!

Note that while the white dress and the background is really good, the color and contrast of the face is just way off! It is actually really tricky to correct such a thing! Just reverting to a manual Levels adjustment is not at all sufficient to get rid of the off balance.


inCamera 3.1
portrait
Click to see a larger version in a separate window (88 kB).
This image is scanned in SilverFast at gamma 1.0 with the setting '48 Bit HDR Color', assigned a profile produced by inCamera 3.1.

I claim this is very close to the appearance of the real slide on the 5000 Kelvin light table. Subjectively, however, it still looks a tad dark and a tad too much red in the flesh tones. Perhaps a slight enhancement with the Levels control might do good? See next image:

inCamera 3.1, Auto Levels
portrait
Click to see a larger version in a separate window (96 kB).
The previous image with Auto Levels applied in Photoshop. (Note that this is done while we are still in the input working space of inCamera!)

Hmm... It made the whole thing a bit too warm, otherwise it is not too bad.

inCamera 3.1, Adobe RGB > Auto Levels
portrait
Click to see a larger version in a separate window (92 kB).
The previous image converted to Adobe RGB (1998), and then Auto Levels applied in Photoshop.

This version should be compared with the corresponding SilverFast version, since both operate in the Adobe RGB (1998) color space.

It is fairly OK! In practice, rather than using Auto Levels, I would probably set the white point and do some minor adjustment with the curves to get it the way I want, but that is more because of preference than adherence to the actual slide.

The lesson to be learnt from this experiment, however, is that the color space of the image can strongly effect the outcome of some adjustments. In this case, it seems much better to convert to some working space, such as Adobe RGB (1998), before doing any color balancing. The strange thing is that in a problematic image, we came to the opposite conclusion when we wanted to lift the shadows!


Scarse 0.3
portrait
Click to see a larger image in a separate window (88 kB).
This image should be compared with the first inCamera version shown above. It is treated the same, but using the Scarse profile instead.

It is actually extremely close the the inCamera version. There are some slight differences though, and I claim that the inCamera version has a slight edge in accuracy.


CONCLUSION
Of the tested profilers, Pictographics InCamera delivers the best result, as seen on a portrait that has everything from deep shadows to bright highlights.

The Scarse profile was almost as good.

The SilverFast Ai profiler is not recommended. As long as it is based on the preview of the scan, it does not have any potential. The HDR version of SilverFast, however, may have potential, since it works very differently.

The application of Curves or Levels to enhance the image will amplify any imperfections in a profile. The more you need to tweak your images, the better profile you need! Perhaps somewhat surprising is the fact that the order in which you convert to a color space and do the enhancements is very important! For color balancing, it seems best to do that after you have converted to a working color space, such as Adobe RGB (1998). For strong lifting of shadows, however, it may be better to apply Curves (or similar tools) while still in the input color space, as was exemplified in a problematic image.

Back to the beginning of the article.

Harald E Brandt
Hägersten, Stockholm
Sweden
Photo: http://photo.bragit.com
BragIt: http://bragit.com
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Last updated: 2011-10-27 at 15:07:10 +0200