This page provides a quick overview
of the toolbars and deals with the basic tonal correction tools, Histograms,
White and Black Point tools, and finishes with the Auto
Colour Correction tool.
Know your tools!
Colour Management Enabled
Management via Embedded ICC Profile
ColorSync/ICC Colour Management Enabled
Variations of the Auto Adjust
Special Functions Toolbar
Assess the Image
After pre-scanning the image it is generally helpful to establish the tonal range of the original and the
location of the darkest and lightest pixels. Using the Black or
point tool located at the
bottom of the Special Functions toolbar we can easily find dark
and light pixels. The location is identified with a red circled cross-hair. If there
is a large numbers of equally light pixels at this point then pressing the White button will cause ALL of these
pixels to turn BLACK. Large numbers of equally dark pixels in the image
will show as WHITE when we press the Black button. I find
this a much more intuitive approach than Photoshop's clipping display since it only
effects those pixels that are likely to be of interest.
SilverFast at Work (Figure
As shown in following screenshot we can also see the actual RGB/CMYK/Lab values for
these pixels in the Densitometer window. The group of
numbers shown circled in red represent the original values. The
numbers on the right represent the corrected values. Obviously since
both the left and right number groups are equal this
screenshot represents the image before any corrections have been
If a single densitometer was all that we got then
would be little to celebrate as the information and location of the
dark and light pixels would be lost as soon as we clicked another
area of the image with the mouse
tool. However, a really neat trick is to lock the location of these
pixels on the pre-scan and provide a dedicated densitometer - How?
Easy! - Hold down the Shift key and click on either the White or
point tool and presto a new dedicated densitometer is created. The
location will also be displayed on the image by a small cross-hair
with an associated number
Fixed Point(s) Densitometer
Furthermore, we can open the Levels or as
LaserSoft call it the Histogram at any
time and see the actual spread of data from dark to light for each of the
channels (RGB, CMYK, etc.). The following screenshot shows the
ideal method of display for best practice colour editing (i.e. all
three RGB channels in view). Here we can see the 3 colour channels.
Histogram - No Adjustments
What does the above histogram tell us? Firstly that
the sample image is not full-scale, i.e. the image has no pixels at level 0
255. We can also see that the shadow and highlights are not completely
neutral. So the histogram provides us with confirmation of what the
Black/White point tool and densitometer was indicating.
Should I use Auto Adjust?
Lots of SilverFast users shy away from the Auto Adjust
thinking that it
is going to damage their images. Maybe it will
and maybe it won't - but the USER has control. By getting a basic
understanding of how
Auto Adjust works we can save ourselves a lot of agony.
LaserSoft have provided an exceptionally powerful tool and we
should learn to use it. Note that in the
screenshot shown below I show Auto
Contrast as OFF - this is my normal approach - others
are free to choose otherwise (Experiment!). The settings shown
inside the red boundary are the KEY to ensuring that minimal data
is lost whilst getting the best from a well exposed and normal
toned original. Read
Chapter 5 of the user manual, read it again, then configure
the Auto section of the SilverFast Defaults window correctly and you won't be sorry.
setting the highlight offset to 0 is
not a good idea since the highlight pixels will be clipped
to level 255 upon application of Auto Adjust.
setting the shadow offset to100% is
good idea since the shadow pixels will be clipped to Level 0
upon application of Auto Adjust.
Auto Defaults (Figure 2)
The following screenshot shows the histogram for
my sample image after pressing the Auto Adjust button (using the settings I suggested above). Simply pressing the Auto Adjust button
will mean that the image highlight and shadows will be optimised
such that the spread of image data is more evenly distributed
(figure 3). Notice how the shadow and highlight points in the
histogram are all equal which means no colour correction has been applied
to the image; I'll explain why in a moment.
Histogram after Auto Adjust
We can also see from our previously created
densitometers that the values for the dark and light points have changed
after applying the Auto Adjust
If the original pre-scan was assessed as being
dark/light by SilverFast then an appropriate correction will
automatically be applied (figure 4). In the screenshot shown below I show
an adjustment of -4 (brighten the image). Positive numbers
will darken the image.
Histogram after Auto Adjust
Important note about Auto
For SilverFast users with IT8 calibration or a
customised ICC scanner profile SilverFast will ignore any colour
casts it finds in the pre-scan and so Auto Adjust will simply
correct the tonal range of the image. If on the other hand you are
using SilverFast without the benefit of calibration then
SilverFast will automatically remove any colour casts found in the
image (not a good
idea for sunsets). The user can preset the amount of
cast removal by inserting a value into the Color Cast Removal popup
shown with a green asterisk (see
Figure 2 above for an example). The default value of 100% will
completely remove the colour cast an a value of 0% will leave the
cast untouched. Alternatively we can hold down the Shift key when pressing
and the colour cast will be retained in all its glory. We can identify whether
SilverFast will or will not automatically apply colour correction by
checking which form the Auto Adjustment (aperture symbol)
takes in the Adjustments toolbar (see Auto Adjust tool
variations on page 1).
Colour cast removal can be
fine-tuned at any time using the Color Cast Removal slider.
The screenshot below shows how smart SilverFast is at removing
colour casts using the Colour Cast Removal slider. I push one
slider and SilverFast decides which channels, if any, require
adjustment to neutralise the cast. As mentioned above; no colour cast removal is Zero
% and complete colour cast removal is 100%. In the example below I show 75% of
the cast has
been removed. Remember not all colour casts are bad, some are an
inherent feature of the image (sunset).
Notice that through careful choice of values for the
Shadow and Highlight Threshold in the Auto
Defaults dialog (figure 2 above) I have managed to ensure that
no clipping occurs at the end points. In this example the end points
were defined as 98% for the shadow which equates to Level 5 and 2% highlight
which equates to Level 249. If we can manage to avoid clipping at
the scan stage we can be confident that saturation of individual
colour channels has also been avoided
Note that any spikes (there might not be any) in
the histogram represent values that have been rounded (made the
same) and usually results from the high to low bit conversion. Gaps
in a histogram represent data values that have been lost. In
simple terms pressing the Alt/Option key when viewing the histogram will
represent the 8-bit data being output to Photoshop. It's also
important that we remember EVERY edit and conversion will loose data. Even applying the basic and very
necessary gamma adjustment to the raw scan will loose data.
So what have we learned from this tutorial:-
The basic tools
How to assess the Pre-scan
Find and store the location of darkest and lightest
Configuration of the Auto Adjustment
How to use the Levels Histogram tool
How the maximise the range of the scan
How to brighten/darken the scan
Automatic and manual Colour Cast Removal
How using the Alt/Option key and Levels
Histogram we can preview
the "edited data" being sent to Photoshop.