\documentclass[final,slideColor,default]{prosper}
                                % START Preamble
\title{Digital Darkroom with the GIMP}
\author{Yoni Rabkin}
\email{yoni-r@actcom.com}
\slideCaption{Digital Darkroom with the GIMP}
                                % Change footnotes to include parenthesis
\makeatletter
\renewcommand\@makefnmark{\@textsuperscript{\normalfont(\@thefnmark)}}
\makeatother
                                % END Preamble
                                % START Document
\begin{document}
\maketitle

\begin{slide}{Abstract}
  This lecture first talks about setting up our computer for working with digital images using the GIMP and GNU/Linux. Then we introduce a number of GIMP tools and editing techniques that we can use to improve our digital images.
\end{slide}

\begin{slide}{Contents}
  \begin{itemize}
  \item What is the GIMP?
  \item Why all the setting up?
  \item Monitor bit depth, color balance and gamma
  \item Monitor resolution
  \item The histogram
  \item Curves tool
  \item Unsharp mask
  \item HSV color model
  \item Contrast mask
  \item Soften
  \item Tungsten white balance
  \item Channel mixer B/W
  \end{itemize}
\end{slide}

\begin{slide}{What is the GIMP?}
  \begin{itemize}
  \item ``The GIMP'' stands for ``the GNU Image Manipulation Program''
  \item Web site [http://www.gimp.org/]
  \item As of 23/03/2004 GIMP version 2.0 has been released and is available for everyone to download. This lecture refers to GIMP 2.0 and not GIMP 1.x that comes with most of the current\footnote{April of 2004} GNU/Linux distributions.
  \item GIMP 2.0 is a major step forward in both performance and usability, hence this lecture will focus on it solely.
  \end{itemize}
\end{slide}

\begin{slide}{Why all the setting up?}
  Before you begin to work in your digital darkroom there are some important things that have to be set up properly. These things are roughly equivalent to a traditional darkroom technician checking that all the chemicals are fresh, that the chemical baths are the right temperature etc. Setting up promises more consistency, quality and speed.
\end{slide}

\begin{slide}{Bit Depth}
  Set your monitor to 24 or 32 bit color depth mode. In 24 bit color depth mode:
  \begin{itemize}
  \item Every pixel on the screen is made up of 3 color channels: Red, Green and Blue.
  \item Each channel is represented in the computer by 1 byte = 8 bits, allowing for 256 levels of that channel.
  \item Three channels per pixel. With 8 bits per channel is 8+8+8 = 24. 24 bits per pixel.
  \item The number of possible colors is \(2^{8*3}=16,777,216\).
  \item GIMP Versions 1.x and 2.0 are natively RGB 8-bits per channel (24bpp)\footnote{This is why we set the monitor to 24bpp too}.
  \item Native 16-bit and CMYK support coming in the future.
  \end{itemize}
\end{slide}

\begin{slide}{Bit depth cont.}
  Examples of bit depth modes besides 24bpp.\footnote{bpp stands for Bits Per Pixel}
  \begin{itemize}
  \item 16bit/16bpp is 5bits red + 6bits green(eye more sensitive) + 5bits blue. \(2^{5+6+5}=65,536\) colors.
  \item 32bit/32bpp is 8bits red + 8bits green + 8bits blue = 24 + 8bits opacity per pixel. \(2^{8*3+8}=4,294,967,296\) colors.
  \item 48bit/48bpp is 16bits red + 16bits green + 16bits blue. \(2^{16*3}=281,474,976,710,656\) colors. Cinepaint [http://cinepaint.sourceforge.net/] is a GIMP based free/open source software project with the ability to support 48bit per pixel images. Cinepaint is used extensively in Hollywood.
  \end{itemize}
\end{slide}

\begin{slide}{Setup: Color Balance}
  \begin{itemize}
  \item Set the black point with the ``brightness'' and ``contrast'' (misnomers).
  \item What is color temperature?
  \item Typical color temperatures:\footnote{Taken from the ``Kodak Professional Photo-guide''}
    \begin{itemize}
    \item $2800\,^{\circ}$K 75 Watt bulb
    \item $3100\,^{\circ}$K sunrise, sunset
    \item $5500\,^{\circ}$K Standard daylight
    \item $12,000\,^{\circ}$K Clear skylight, open shade
    \end{itemize}
  \item Set your monitor to the 6500K white point. Use Yoni's ``piece of paper and an open window'' method.
  \end{itemize}
\end{slide}

\begin{slide}{Setup: What is monitor gamma?}
  What is gamma? Why set it? Because monitors don't react linearly to increased voltage,
  \begin{equation}
    output luminance=\left(\frac{input[0,255]}{255}\right)^{gamma}
  \end{equation}
  \begin{equation}
    output luminance=c+\left(\frac{input[0,255]}{255}\right)^{gamma}+b
  \end{equation}
  Is there more detail in the shadow areas of my photos that I'm not seeing? How about the highlights? How can I get predictable results?
\end{slide}

\begin{slide}{Setup: Monitor gamma}
  \begin{itemize}
  \item Typical gamma targets:
    \begin{itemize}
    \item 1.8 - original Apple Macintosh
    \item 2.5 - IBM PC compatibles
    \item 2.2 - Microsoft/Hewlett-Packard/Pantone/Corel sRGB ``standard Internet color space''
    \end{itemize}
  \item Monitor age and quality
  \item View$\rightarrow$ Display Filters$\rightarrow$ Gamma
  \end{itemize}
\end{slide}

\begin{slide}{Setup: xgamma example}
  Follow the instructions at the Web site: \ptsize{10}[http://users.dslextreme.com/$\sim$craig.lawson/linux\_notes/color.html]\ptsize{12}. Craig Lawson has a wonderful page there with easy to follow instructions. The long and short of it is:
  \begin{itemize}
  \item Display the gamma pattern appropriate for your gamma target
  \item Read the existing gamma value with:
\begin{verbatim}
        xgamma
\end{verbatim}
  \end{itemize}
\end{slide}

\begin{slide}{Setup: xgamma example (Cont.)}
  \begin{itemize}
  \item View the gamma pattern and then adjust the new gamma value toward the target, for example:
\begin{verbatim}
        xgamma -gamma 1.3
\end{verbatim}
  \item Add the gamma adjustment to your xinitrc or xsession scripts, for example:
\begin{verbatim}
       /usr/X11R6/bin/ xgamma -gamma 1.43
\end{verbatim}
  \item Test that your adjustment has been preserved after restarting your X session:
\begin{verbatim}
        xgamma
\end{verbatim}
  \end{itemize}
\end{slide}

\begin{slide}{Setup: Monitor Resolution}
  Monitor resolution and file sizes\footnote{No such thing as ``f\mbox{}ile resolution!''}:
  \begin{itemize}
  \item 1024x768 minimum
  \item Average 17'' monitor 72ppi\footnote{PPI = Points Per Inch}
  \item Image sizes for the Web vs. for printing:
    \begin{itemize}
    \item The computer monitor is a low-resolution medium. A Web photo can be 100 to 200 Kilobytes in size as a compressed JPEG image.
    \item The print is a high-resolution medium. A print can be generated from a 10 to 50 Megabyte raw (meaning uncompressed) image.
    \end{itemize}
  \end{itemize}
\end{slide}

\begin{slide}{Tools: The Histogram}
  \begin{itemize}
  \item What is it? Control luminosity throughout
  \item Where? 
    \begin{itemize}
    \item Dialogs$\rightarrow$ Histogram
    \item Layers $\rightarrow$ Colors$\rightarrow$ Levels
    \end{itemize}
  \item When?
    \begin{itemize}
    \item Large contrast adjustments
    \item Cleaning homogeneous areas
    \item Calibration (middle gray)
    \end{itemize}
  \end{itemize}
  Beware the dreaded toothcomb aka. ``fingers of death''
\end{slide}

\begin{slide}{Tools: Curves}
  \begin{itemize}
  \item What is it? Fine control of luminosity
  \item Where? Layer$\rightarrow$ Colors$\rightarrow$ Curves
  \item When?
    \begin{itemize}
    \item Fine contrast adjustments
    \item Localized adjustment
    \item Images lacking ``punch'' (S-curve)
    \end{itemize}
  \end{itemize}
  Always fix the 50 percent (middle) point, otherwise you might do violence to the image!
\end{slide}

\begin{slide}{Tools: Unsharp Mask}
  \begin{itemize}
  \item What is it? Brighten the bright and darken the dark at object edges, image appears sharper
  \item Where? Filters$\rightarrow$ Enhance$\rightarrow$ Unsharp Mask
  \item Ballpoint for 1024x768 image: 
    \begin{itemize}
    \item Radius: 1.0 (How wide edge becomes)
    \item Amount: 0.50 (How much)
    \item Threshold: 1 (How far apart values before applying)
    \end{itemize}
  \item When?
    \begin{itemize}
    \item Scanned film/photographs
    \item No perceptual sharpness
    \end{itemize}
    Last, last, last thing you do to an image!
  \end{itemize}
\end{slide}

\begin{slide}{Tools: Unsharp Mask (Cont.)}
  \begin{itemize}
  \item Ansel Adams\footnote{Ansel Adams[1902-1984], Landscape photographer and inventor of the ``Zone System''} once said: ``There is nothing worse than a sharp image of a fuzzy concept.'' Proof enough is Robert Capa's ``Omaha beach''\footnote{Robert Capa[1913-1954], War photographer, his photo ``Omaha Beach'', http://www.andrewsmithgallery.com/images/magnum/RC\_1074.jpg} from 1944. Don't over-sharpen.
  \item How not to over-sharpen?
    \begin{itemize}
    \item Always perform sharpening with the image at 100 percent magnification.
    \item Hunt for artifacts.
    \item Sharpen for perceptual effect, a sharp Web image does not equal a sharp printout.
    \end{itemize}
  \end{itemize}
\end{slide}

\begin{slide}{Tools: HSV color model}
  \begin{itemize}
  \item What is it? Transform colors in HSV space, Yet Another Color Model equivalent to RGB space
  \item HSV? Hue ($0-360\,^{\circ}$), Saturation (Purity 0-1), Value (Lightness 0-1)
  \item Where? Layer$\rightarrow$ Colors$\rightarrow$ Hue-Saturation
  \item When?
    \begin{itemize}
    \item Wanting Fuji Velvia or National Geographic saturation
    \item Lighting correction (see Techniques: Tungsten white balance)
    \end{itemize}
  \end{itemize}  
\end{slide}

\begin{slide}{Techniques: Contrast Mask}
  \begin{itemize}
  \item What is it? Controlling contrast
  \item When?
    \begin{itemize}
    \item Information hidden in the shadows (and highlights)
    \item Sending to uncalibrated monitors / printers
    \end{itemize}
  \item How?
    \begin{itemize}
    \item Duplicate Layer (the following only on the top layer)
    \item Layer$\rightarrow$ Colors$\rightarrow$ Desaturate
    \item Layer$\rightarrow$ Colors$\rightarrow$ Invert
    \item Filters$\rightarrow$ Blur$\rightarrow$ Gaussian Blur
    \item Layers Mode: Overlay
    \item Adjust opacity
    \end{itemize}
  \end{itemize}
  Beware of boring ``flat'' images!
\end{slide}

\begin{slide}{Techniques: Soften}
  \begin{itemize}
  \item What is it? Softens the image
  \item When?
    \begin{itemize}
    \item Portraits with problematic skin texture
    \item Movie poster effect wanted
    \end{itemize}
  \item How?
    \begin{itemize}
    \item Duplicate Layer and set top layer to ``Multiply''\footnote{Use the ``Layers'' dialog window}
    \item Using Levels, set bottom layer gamma to 1.70
    \item Using Levels, set top layer gamma to 2.70
    \item Slightly over-sharpen top layer\footnote{Filters$\rightarrow$ Enhance$\rightarrow$ Unsharp Mask / Sharpen}
    \item Blur lower layer
    \end{itemize}
  \end{itemize}
\end{slide}

\begin{slide}{Techniques: Tungsten white balance}
  \begin{itemize}
  \item What is it? Fixes orange color cast
  \item When? Tungsten lighting with no white balance
  \item How?
    \begin{itemize}
    \item Layer$\rightarrow$ Colors$\rightarrow$ Hue-Saturation
    \item Reduce the ``Saturation'' for yellow to -30
    \item Reduce the ``Saturation'' for red to -30
    \end{itemize}
  \end{itemize}
  If a known color exists in the image, create a reference square.

  Beware not to create ``dead'' skin tones.
\end{slide}

\begin{slide}{Technique: Channel Mixer B/W}
  \begin{itemize}
  \item What is it? Allows for better black and white images
  \item When? 
    \begin{itemize}
    \item Turning a color image to black and white selectively
    \item Choosing the best channel for scanned B/W negatives
    \end{itemize}
  \item How?
    \begin{itemize}
    \item Filters$\rightarrow$ Colors$\rightarrow$ Channel Mixer
    \item Choose ``Monochrome''
    \item Mix amounts of RGB for desired affect.
    \end{itemize}
  \end{itemize}
\end{slide}

\end{document}
                                % END Document
