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Quicktip: Expanding the dynamic range of your pictures with HDR scan mode and Multi-Exposure (Part I HDR scan type)

July 30th, 2010 · 4 Comments · News

Photographically speaking, we tend to believe that what we see is all we get and there is no room for improvements.
Shoot your pictures in a color negative filmstrip and get copies of those on paper or shoot with your digital camera and opened those on your computer to see the result on the screen.
We think what we have in front is all we got. right?

Wrong, there is more to it!

Usually paper prints and computer screens have a relatively limited capacity in terms of dynamic range.

In photography “dynamic range” is the ratio between the lightest and the darkest values a photographic medium is capable of capturing or showing. In simple words, the amount of shades between white and black captured or displayed by the film, paper prints, slides, a digital camera or screen.

These are not standard and the same to all them, regularly films and digital cameras have a broader dynamic range than paper prints or computer screens (or the digital camera screen).

The details we do not see in the paper print or the screen can still be captured and used later to your advantage.

For this purpose you need two things:

  • Set your SilverFast to 48 bit HDR or 64 bits HDRi
  • and Multi-Exposure (This is a separately sold extra tool in SilverFast  and your scanner must support this feature).

Setting SilverFast to scan in HDR mode

There are two types of HDR scans for color and two types for black and white, not all of them are available for all scanner models; some old scanner models might not even have any of this options available because of their capabitilities.

To activate any of the HDR scanning modes, go to the frame tab and in the menu “Scan Type” select the option 48 bit HDR color or 64 bit HDRi color for color slides or Negative filmstrips; the  16 bit HDR greyscale or 32 bit HDRi greyscale are intended for black and white film material.

Frame panel, HDR scan types

The 48 bits HDR color scan mode creates a raw file of your picture, which means a completely unmodified file (or if you prefer, you can call it a digital negative) which assigns 16 bits to every of the tree color components: red, green and blue; hence 48 bits.

The 64 bit HDRi color scan mode creates the same kind of file with an extra channel containing information from the infrared channel (not all scanners are capable of this). The additional advantage to the 48 bit HDR file is that the infrared channel can later be used to get rid of scratch and dust spots in the film.

The 16 bit  HDR greyscale has just one channel with 16 bit in shades of grey and the 32 bit HDRi greyscale has one 16 bit channel with shades of grey and one 16 bit channel with infrared information for correction of dust and scratches.

You might be wondering what a difference does it really make to have 8 bits or 16 bits files.

8 bit files or 8 bits per channel (in the case of color pictures 24 bits) means that you have aprox. 250.000 shades of grey or of one color to represent your picture. 16 bit files have aprox. 16’000.000 shades of grey or one color per channel to represent your picture.

By using any of these scan types combined with the extra information contained in your film already present a huge improvement with respect  to the images in 24 bits (in the case of color pics) or 8 bits (in the case of black and white) that you are used to or that your computer monitor (8 bits) are capable of. However combining HDR with Multi-Exposure will give you the extra power to extend the dynamic range of your pictures (among other advantages).

The next article will explain how to use Multi-Exposure in combination with HDR scantypes.

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