SilverFast AI & HDR

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Tutorial - 8

Basic Image Editing - Histogram

By Ian Lyons

 

 

LOGO

A Computer Darkroom Tutorial

 
This tutorial will attempt to help the new user to better understand the range of colour and tone editing tools to be found within SilverFast. I don't intend to give a detailed account of each tool but simply highlight those that appear less than obvious/friendly to many SilverFast users.
 

Editing the Prescan in SilverFast Ai and HDR

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!

 

Image

Adjustments Toolbar

 

 

B1 B2 B3

No Colour Management Enabled

Colour Management via Embedded ICC Profile

ColorSync/ICC Colour Management Enabled

Variations of the Auto Adjust Tool

 

Image

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 White point tool B4 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.

 

Image

SilverFast at Work (Figure 1)

 

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 applied.

 

Densitometer

Densitometer

 

If a single densitometer was all that we got then there 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 Black 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

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 nor 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.

 

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