Raw Notes - Canon CHDK User Manual

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RAW notes

It may be said that CHDK owes it's existence to the desire for saving RAW in RAW barren Powershot
cameras. By inspired work on the Firm update procedure with these cameras, it was discovered that
RAW was actually a disabled function of the original firmware, and with further genius, enabling RAW
saving and other functions saw the beginnings of the CHDK.
The name RAW actually suggests that this is a file without any changes straight from the camera's
sensor, and with CHDK this is the case. In some cameras this is not the case, some have had some
kind of processing such as sharpening, adding of a header file, Exif data, compression, and even white
balance, it could be suggested even unknown processing (except to the manufacturer).
Knowing that the RAW file will contain more depth or digital information is the motivator for saving
RAW, so that in processing, more digital information is available to work with.
Most RAW enabled cameras save as 12 bits per pixel or 14 bits per pixel whereas CHDK is 10 or
12 bpp, depending on the camera model, this is still far more than the 8 bit JPEG depth, This means you
can make a wider range of adjustments without compromising picture quality.
RAW is therefore a powerful option that most advanced digital cameras make available to photographers
who do not want the camera to apply any in-camera processing to the captured RAW data, preferring to
do that themselves in post-processing. Shooting with RAW still has a fundamental principle to apply
though - it won't correct mistakes that are made in the shooting procedure, exposure and other parameters
are still required to be correct at shoot time for a high quality image. You cannot take a grossly
underexposed or overexposed picture in RAW, and expect to be able to "correct your mistakes".
RAW data takes longer to write to a memory card and there is a need to post-process every single picture.
These two requirements might be a major hindrance depending on the type of photography you do. If
you need to take pictures in rapid succession, and your digital camera does not provide a large enough
RAW buffer, you will be hampered by the extra amount of time it takes to write a large RAW image file
to the memory card. Camera RAW files are typically 2–6 times larger than JPEG files. While use of RAW
formats avoids the compression artifacts inherent in JPEG, fewer images can fit on a given memory card.
Post-processing every single image is also a chore that not many amateur photographers (and some
professional photographers) enjoy doing. This means that, for most practical purposes, amateur
photographers will find that saving in RAW is not an interesting option, and that shooting in JPEG is
more than sufficient.....Unless...You are unsure of the white balance to use or need accurate colour
reproduction of a subject, or you want optimum control over sharpness, contrast, saturation;
Many photographers are finding that they do want the control that RAW gives them.
With some cameras, and also with CHDK, you can have the advantage of saving RAW and JPEG, this
means having the option to just keep the RAWs that you need for optimum processing, or otherwise just
keeping the JPEGs if you are pleased with the camera's processing. For many, saving in JPEG is more
than adequate. JPEG files are compressed, and, compared to RAW, they are smaller, save faster, and more
images can fit on a memory card. Many professional photographers shoot at the highest JPEG image
quality. Remember also RAW can be disabled for certain shooting conditions, see the RAW parameters
menu for "Disable RAW @ burst" etc.
There is no single RAW format; formats can be similar or radically different. Different manufacturers use
their own proprietary and typically undocumented formats, which are collectively known as RAW
format. The DNG (Adobe) format has been put forward as a possible universal standard. Using the DNG
format also means being able to work with the files in the future if other proprietary methods disappear.
Processing CHDK RAW is possible using a number of available applications, particularly DNG4PS-2,
free software created for CHDK, others are listed at the CHDK Wiki.
Recently it has been recommended to use the in camera DNG conversion, producing a widely compatible
DNG image file, recognized by the popular image editors. Using the DNG format also has the advantage
of downloading over USB, including the Exif data from the corresponding JPEG.
See: Downloading via USB, on page 46.