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IXUS 100 (SD780) - is CHDK RAW really beneficial?

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Offline Comfy

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IXUS 100 (SD780) - is CHDK RAW really beneficial?
« on: 19 / July / 2010, 20:02:20 »
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Hi All,

Firstly, just wanted to say thanks to all involved in CHDK - I am thinking of buying an Ixus 100 IS and wanted to know if the RAW output really is much to write home about.  I shoot in RAW with my Fuji camera and would never shoot in JPEG again given the choice - but I have seen an example of a CHDK IXUS 100 DNG against its jpeg and there was not that much difference.

I also have seen a post on here saying shadow detail and exposure etc is not somethng that will give you much results in CHDK RAW as opposed to regular RAW.

Just wondered if anyone has used the IXUS 100 and what they think of the RAW output from the amazing CHDK.

Thanks alot peeps! :-)
Comfy
(PS) Any other comments about CHDK on the IXUS 100 IS would be appreciated as I am still undecided if it is a worthwhile purchase for me.  I am only looking at that model  but will only buy it if the CHDK does make it worthwhile.
Again - GREAT WORK!!!!
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Offline bart100IS

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Re: IXUS 100 (SD780) - is CHDK RAW really beneficial?
« Reply #1 on: 21 / July / 2010, 16:49:22 »
Raw does make sense in the 100IS. Gone are the oversharpening and noise reduction starting at iso 80. It's a joy to see pixels with the real image information versus a cheap interpretation of what you expected in jpeg. It gets even better at iso 200 and iso 400. Very useable. And ofcourse WB correction is a must have. Very happy with CHDK in the 100IS.
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Offline ixussuxi

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Re: IXUS 100 (SD780) - is CHDK RAW really beneficial?
« Reply #2 on: 01 / August / 2010, 22:57:36 »
I have just installed CHDK on my 100IS and this is my first post - so again thanks to the developers for this mind-boggling hack!

It is quite an eye-opener to see the RAW files. There is massive barrel distortion at the wide end of the zoom, and similarly massive noise at ISO400, both of which are substantially reduced by the in-camera JPEG processing. I estimated some lens parameters for the former (will post if there is interest) and dcraw's wavelet noise reduction improves the latter. Haven't checked on chromatic aberration yet.

Generally I think Canon's JPEG processing is excellent. But if you are skilful and prepared to hand-tune individual images then I can believe you might be able to do a bit better. Nice to have the option.

My SD card is not very fast and saving the DNG (only version I can read) slows things down a lot.
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Offline Microfunguy

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Re: IXUS 100 (SD780) - is CHDK RAW really beneficial?
« Reply #3 on: 02 / August / 2010, 10:11:54 »
Quote from: ixussuxi on 01 / August / 2010, 22:57:36
I estimated some lens parameters for the former (will post if there is interest)

Yes, that is of interest.

I was not aware that the Canon JPG processing also applied some lens-distortion correction.



David
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Offline ixussuxi

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Re: IXUS 100 (SD780) - is CHDK RAW really beneficial?
« Reply #4 on: 02 / August / 2010, 11:08:28 »
Quote from: Microfunguy on 02 / August / 2010, 10:11:54

Yes, that is of interest.

I was not aware that the Canon JPG processing also applied some lens-distortion correction.

OK. I am using Imagemagick to transform the image, so the parameters I have relate to the formulas given here: http://www.imagemagick.org/Usage/distorts/#barrel

Rather than attempting to actually straighten lines, I just tried to reproduce the existing 100IS JPEG correction. Here's the values (Focal Length, C, D):

6mm,   -0.043399,  1.01963
7mm,   -0.025316,  1.01210
8.7mm, -0.008984,  1.00505
11mm,  -0.008002,  1.00355
15mm,  -0.000465,  1.00043
18mm,   0.001663,  0.99865

The A & B parameters did not make any noticeable difference, so I took them to be zero. I will probably just linearly interpolate for other focal lengths.

(On linux) I first convert DNG -> TIFF using dcraw, then correct distortion with e.g. at 6mm:

convert CRW_0559.tiff -distort Barrel "0.0 0.0 -0.043399 1.01963" corrected.tiff

Sorry if the lens parameters are not the standard ones. It should not be hard to transform them to some other scheme.
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Offline Microfunguy

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Re: IXUS 100 (SD780) - is CHDK RAW really beneficial?
« Reply #5 on: 02 / August / 2010, 12:28:39 »
You say that the JPG image has less lens distortion than the RAW image.

Do you have any JPG + RAW  image that shows this ?
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Offline ixussuxi

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Re: IXUS 100 (SD780) - is CHDK RAW really beneficial?
« Reply #6 on: 02 / August / 2010, 19:46:54 »
Quote from: Microfunguy on 02 / August / 2010, 12:28:39
You say that the JPG image has less lens distortion than the RAW image.

Do you have any JPG + RAW  image that shows this ?

I photographed a grid on my computer monitor. Here's the comparison at 6mm (JPEG on left is from RAW on right):



The numbers given above match the grid on the RAW to the grid on Canon's JPEG. For no correction C=0 and D=1. D is a just a scale factor while C measures actual distortion. You can see the barrel falls away quite rapidly as focal length increases, turning into very slight pincushion at the tele end.

The camera must do the correction in real time, as the distortion does not appear on the LCD either!

I also wonder if the JPEG processor does anything about vignetting. I should look into that.
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Offline reyalp

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Re: IXUS 100 (SD780) - is CHDK RAW really beneficial?
« Reply #7 on: 03 / August / 2010, 13:32:06 »
Quote from: Microfunguy on 02 / August / 2010, 10:11:54
I was not aware that the Canon JPG processing also applied some lens-distortion correction.
Several recent cameras do this AFAIK. Chromatic aberration too.

Quote from: ixussuxi on 02 / August / 2010, 19:46:54
The camera must do the correction in real time, as the distortion does not appear on the LCD either!

I also wonder if the JPEG processor does anything about vignetting. I should look into that.
We could do many interesting things if we could figure out how to program the image processing part of Digic rather than just the ARM (if it is programmable...)
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Offline ixussuxi

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Re: IXUS 100 (SD780) - is CHDK RAW really beneficial?
« Reply #8 on: 07 / August / 2010, 01:04:12 »
I have a batch script for processing DNG files from my DSLR, based on dcraw and imagemagick. I tried it on the 100IS DNGs, just tweaking the contrast a bit to bring the result closer to Canon's JPEG. Here's the comparison - Canon's JPEG on left, processed DNG on right, 100% crop from centre of frame and ISO160:



The DNG conversion also includes a correction for chromatic aberration, using fulla and parameters given by tca_correct, but to my eyes it didn't make a noticeable difference.

To me there appears more detail in the CHDK/DNG version and I think the full image on screen has a bit more punch. A neutral observer I asked also preferred the on-screen DNG version, saying it looked more 'realistic'. But not a huge difference.

IMO if the image is important enought to you that you are likely to postprocess it anyway it is definitely worth having the DNG. Otherwise probably not, as it will slow down the camera, fill up your SD card and the result may not be so different (unless you are better at this than me).

Disclaimer: I am not a PP expert. I am just using free software. It's likely better results are possible. Also I didn't try different camera JPEG settings.
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Offline PS

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Re: IXUS 100 (SD780) - is CHDK RAW really beneficial?
« Reply #9 on: 07 / August / 2010, 14:49:18 »
Increasing midtones contrast will compress shadows and/or highlights. It seems to me that many Canon p&s produce JPEGs with such characteristics i.e. compressed and desaturated shadows. This looks especially bad when you have much shadow in the scene.
Besides curved characteristic and other unnecessary processing, there is color space clipping. As displays progress (offering wider gamut and contrast) you develop images accordingly.
In general, RAW stores actual information of a scene that was captured rather than reduced and further processed/manipulated to look on typical display as manufacturer chosen.
« Last Edit: 08 / August / 2010, 10:49:04 by PS »
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