andremetal
Yes, he can make HDR photos using only one RAW file. You can set differents exposures when you working with RAW. Set 3 or 4 differents exposures, save 4 JPG, merge they and voilá, you have your HDR photo. This is useful when you can´t do the bracketing like when you taking shots of the sea, or sports.
For the A590-IS, this probably isn't worth the trouble. The RAW files only have 10 bits of dynamic range, and the JPEG files have 11 bits of dynamic range, compressed into 8 bits with a gamma curve. A good RAW converter (such as RawTherapee) should perform highlight/shadows recovery to restore detail, and it will probably look more realistic than the multiple-photo HDR from the same scene. The dark current on longer exposures will further reduce your usable RAW dynamic range. See below for calibration of colors in the RAW converter.
Proper Exposure Bracketing:
Turn OFF the "Save RAW" option, or set it to only save the first image in the series. Otherwise bracketing may crash, lag heavily, or badly overexpose. Go to "Extra Photo Options" in the menu, and select "Bracketing in continuous mode." Set a Tv Bracketing value of 1-2 Ev, and then shoot in continuous mode -- it will start at your default exposure and shoot an exposure bracket with increasing range for as long as you hold the shutter down.
vinmar
@bugmenot: CRW is a raw file (Canon Raw -> CRW (?))
All raw files should be the same dimensions, for an A590 it will always be 8 megapixels.
The RAW file is actually a bit higher in resolution than the JPEG output. This is because the camera shoots a little extra information on the sides to prevent problems with demosaicing/denoising the edges of the image (10-30 pixels for this camera, from what I see). There is also a dead zone on the sensor outside of this, which does not produce light, but your RAW software will remove this.
Going from the info for the Powershot A720-IS, which has the same-size RAW file & sensor, the A590-IS has a 3336x2480 sensor, of which 3292x2466 is active area. Some of this gets cropped out after RAW processing by the camera to produce its JPEG file (about 10-30 pixels on each side). So yes, the RAW file will have slightly higher resolution.
Important: Color Calibration for Canon Powershot A590-IS RAW Processing:
Download and use the DNG4PS-2 beta 0.2.3 here:
http://dng4ps2.chat.ru/index_en.html#downloads. Copy the Powershot A720-IS profile, change the camera name, and set Color Matrix #1 to Illuminant="Daylight", and copy in this matrix:
0.401274 -0.100048 -0.074628 -0.054260 0.326804 0.016926 0.026217 0.036974 0.111526
. Then hit OK, and try processing your RAW file to a DNG file. This calibration isn't perfect, but it's better than the alternatives. Looks comparable to the JPEG to me, although slightly darker. I'll post a more precise profile when I have one. The gamma for my calibration was ~1.8 or 1.9.
Proviso: designed for "Daylight" white balance mode.
Tip for reducing noise & camera jiggle in still shots w/ tripod: (works w/out CHDK too!)
Even in ISO80, I get some visible noise & JPEG artifacting. If you select the custom-timer mode, you can tell it to wait a while and then take multiple shots automatically. Set it to ~30 second delay and 4 shots -- that gives time for any tripod/camera motion from pressing the shutter to settle down before shooting. Then you can average the resulting shots together with one of the image stacking programs to reduce noise without any image alignment to correct for camera jiggle. Averaging reduces the noise by the square root of how many shots used. For example, with 4 shots, noise is cut in half (sqrt(4) = 2). With 8 images, noise is reduced by a factor of ~2.83. So, if you use ISO 80, you can get noise equivalent to ISO 40 with 4 pictures, or ISO28 with 8. Example of results:
Cambridge in Color site.
If there are moving objects in the scene (tree leaves, people), they'll be blurred like with slow shutter speeds. This is easy to fix with an image editor: put the averaged image as the top layer, and whichever view of the moving thing you prefer beneath it. Then mask out/erase the parts with moving objects in the averaged image. Bam! No extra motion blur, and everything else has less noise.
You can also add the images together, to get an effectively higher exposure and dynamic range, but more noise (equivalent to a higher ISO setting).
