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<title>Raw convertion parameters</title>
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<h1>Raw convertion parameters</h1>
This page gives some details about the raw image format conversion process that takes place in LuminanceHDR.
<ol>
<li><A href="#intro">Introduction</A></li>
<li><A href="#tweak">Tweaking the conversion process</A></li>
<li><A href="#excerpt">Dcraw manual page excerpt</A></li>
<li><A href="#links">Links</A></li>
</ol>
<A name="intro"><h2>Introduction</h2></A>
<p>
Each time the user:
<ul>
<li>loads a single raw file in the main workspace</li>
<li>specifies a set of raw files in the "File -> New Hdr..." wizard</li>
</ul>
a RAW->TIFF conversion transparently takes place by calling the dcraw [1] executable (by Dave Coffin).<br>
LuminanceHDR calls dcraw to convert a raw file [2] to a (either 8 bit or 16 bit) TIFF file.<br>
<A name="tweak"><h2>Tweaking the conversion process</h2></A>
You can tweak the way dcraw operates by setting specific command line switches (aka options or parameters) in the <em>Tools -> Preferences... -> Raw Import</em> section (here's a screenshot).<br>
<img src="images/raw_conversion.jpg" width="483" height="480"><br>
The -T switch (TIFF output, see <A href="#excerpt">below</A>) is the only required parameter.<br>
In this particular case we have also specified the optional -4 parameter to ask dcraw to obtain a 16 bit (TIFF) file.<br>
Starting with LuminanceHDR 1.9.3 the default options for calling dcraw are -T -4 -q 3.<br>
The dcraw's manual page lists all the available options.<br>
An excerpt is available <A href="#excerpt">below</A>, for the latest manual page follow this reference [3].<br>
<A name="excerpt"><h2>Dcraw manual page excerpt</h2></A>
Here's an excerpt from dcraw's man page (Retrieved: October 30, 2007).</p>
<pre>
OPTIONS
-v
Print verbose messages, not just warnings and errors.
-c
Write decoded images or thumbnails to standard output.
-e
Extract the camera-generated thumbnail, not the raw image. You'll get either a JPEG or a PPM file, depending on the camera.
-z
Change the access and modification times of an AVI, JPEG, TIFF or raw file to when the photo was taken, assuming that the camera clock was set to Universal Time.
-i
Identify files but don't decode them. Exit status is 0 if dcraw can decode the last file, 1 if it can't. -i -v shows metadata.
dcraw cannot decode JPEG files!!
-d
Show the raw data as a grayscale image with no interpolation. Good for photographing black-and-white documents.
-D
Same as -d, but totally raw (no color scaling).
-h
Output a half-size color image. Twice as fast as -q 0.
-q 0
Use high-speed, low-quality bilinear interpolation.
-q 1
Use Variable Number of Gradients (VNG) interpolation.
-q 2
Use Patterned Pixel Grouping (PPG) interpolation.
-q 3
Use Adaptive Homogeneity-Directed (AHD) interpolation.
-f
Interpolate RGB as four colors. Use this if the output shows false 2x2 meshes with VNG or mazes with AHD.
-m number_of_passes
After interpolation, clean up color artifacts by repeatedly applying a 3x3 median filter to the R-G and B-G channels.
-n noise_threshold
Use wavelets to erase noise while preserving real detail. The best threshold should be somewhere between 100 and 1000.
-b brightness
By default, dcraw writes 8-bit PGM/PPM/PAM with a BT.709 gamma curve and a 99th-percentile white point. If the result is too light or too dark, -b lets you adjust it. Default is 1.0.
-4
Write 16-bit linear pseudo-PGM/PPM/PAM with no gamma curve, no white point, and no -b option.
-T
Write TIFF output (with metadata) instead of PGM/PPM/PAM.
-k black
Set the black point. Default depends on the camera.
-K darkframe.pgm
Subtract a dark frame from the raw data. To generate a dark frame, shoot a raw photo with no light and do dcraw -D -4 -j -t 0.
-w
Use the white balance specified by the camera. If this is not found, print a warning and use another method.
-a
Calculate the white balance by averaging the entire image.
-A left top width height
Calculate the white balance by averaging a rectangular area. First do dcraw -j -t 0 and select an area of neutral grey color.
-r mul0 mul1 mul2 mul3
Specify your own raw white balance. These multipliers can be cut and pasted from the output of dcraw -v.
no white balance option
Use a fixed white balance based on a color chart illuminated with a standard D65 lamp.
+M or -M
Use (or don't use) any color matrix from the camera metadata. The default is +M if -w is set, -M otherwise. This option only affects Olympus, Leaf, and Phase One cameras.
-C red_mag blue_mag
Enlarge the raw red and blue layers by the given factors, typically 0.999 to 1.001, to correct chromatic aberration.
-H 0
Clip all highlights to solid white (default).
-H 1
Leave highlights unclipped in various shades of pink.
-H 2
Blend clipped and unclipped values together for a gradual fade to white.
-H 3-9
Reconstruct highlights. Low numbers favor whites; high numbers favor colors. Try -H 5 as a compromise. If that's not good enough, do -H 9, cut out the non-white highlights, and paste them into an image generated with -H 3.
-o [0-5]
Select the output colorspace when the -p option is not used:
0 Raw color (unique to each camera)
1 sRGB D65 (default)
2 Adobe RGB (1998) D65
3 Wide Gamut RGB D65
4 Kodak ProPhoto RGB D65
5 XYZ
-p camera.icm [ -o output.icm ]
Use ICC profiles to define the camera's raw colorspace and the desired output colorspace (sRGB by default).
-p embed
Use the ICC profile embedded in the raw photo.
-t [0-7,90,180,270]
Flip the output image. By default, dcraw applies the flip specified by the camera. -t 0 disables all flipping.
-s [0..N-1] or -s all
If a file contains N raw images, choose one or "all" to decode. For example, Fuji Super CCD SR cameras generate a second image underexposed four stops to show detail in the highlights.
-j
For Fuji Super CCD cameras, show the image tilted 45 degrees. For cameras with non-square pixels, do not stretch the image to its correct aspect ratio. In any case, this option guarantees that each output pixel corresponds to one raw pixel.
</pre>
<A name="links"><h2>Links</h2></A>
<pre>
[1]http://cybercom.net/~dcoffin/dcraw/
[2]http://en.wikipedia.org/wiki/Raw_image_format
[3]http://cybercom.net/~dcoffin/dcraw/dcraw.1.html
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