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raw and nothing but raw sensor information

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raw and nothing but raw sensor information
« on: 09 / August / 2011, 05:12:09 »
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Hi Folks,

Have been enjoying raw on my IXUS100IS for a couple of months now and I am still very impressed by what such a small sensor can show me image quality wise.

So I got the Canon S95 too, to have native RAW, to be able to shoot faster, not having to wait for the AF to pop up.
But the reality is: the S95 files look crippled. This raw is raw that has been worked on NR wise before it is stored on the card. You need heavy sharpening to show the detail of the sensor, but then you end up with an over sharpened file. You can work on it with NR in Photoshop, but it never ends up looking as good as the 100IS file. No problems with prints 11x13 inch, but I want to be able to print 4 x 5 Ft. The 100IS can do that, with the noise looking good. An S95 file on the other hand will look "worked on" at that size. And it is not just the 12 mp versus 10 mp difference. I have seen CHDK 8mp files from a 1/ 2.5 sensor that look better. Besides that the S95 files give me artefacts on fine detail in dog's furs and even in the flesh of someone's face. I suspect Canon's famous HS system is to blame for all this.

So this is my request / suggestion:
Is it possible to document / enlist cameras that work with CHDK and split them in "clean raw" and "worked on" RAW cameras?

To start this list:
IXUS 100IS:  clean RAW
S95: "worked on" RAW

One of the reasons for this request is that I'm interested in more recent compacts, but don't want to go through the hassle of buying and selling them again if the files are as crippled as from the S95.

BTW This post is not meant as a rant about the S95. It's a fine, very fine camera, for prints up to 11x13. Although, personally I find it just a bit too heavy and large too, compared to the 100IS, if carried in my jeans pocket.

Thanks in advance,

Kind regards,

Bart

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Offline fe50

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Re: raw and nothing but raw sensor information
« Reply #1 on: 09 / August / 2011, 05:45:44 »
Is it possible to document / enlist cameras that work with CHDK and split them in "clean raw" and "worked on" RAW cameras?
What RAW files on your S95 do you mean with "...files look crippled" - the CHDK RAW files or the Canon RAW's ?

CHDK RAW files are always unprocessed, a CHDK RAW file is an unmodified sensor data dump.
Canon RAW images may be processed by the original firmware...

With disabled badpixel correction (i.e. without a badpixel.txt file in the \CHDK folder) the RAW file is the real sensor data.

Re: raw and nothing but raw sensor information
« Reply #2 on: 09 / August / 2011, 10:06:46 »
So I got the Canon S95 too, to have native RAW, to be able to shoot faster, not having to wait for the AF to pop up.
But the reality is: the S95 files look crippled. This raw is raw that has been worked on NR wise before it is stored on the card.
So if you don't like the Canon RAW files,  why not enable CHDK RAW instead and use that ?  From what I see in your original post,  that should give you exactly what you want.
Ported :   A1200    SD940   G10    Powershot N    G16

Re: raw and nothing but raw sensor information
« Reply #3 on: 09 / August / 2011, 13:10:00 »
Thanks both waterwingz and fe50 for your quick replies.

I've used the DNG provided by CHDK with the S95, but saw no difference between the CHDK raw and the Canon Raw.
With "crippled" I mean that the pixels don't look as crisp as the pixels in the files produced by my IXUS 100IS. For example, pixelwise the 100IS files look exactly the same as Nikon D2X raw files, both 12mp. The S95 RAW DNG as well as the native RAW files look as if an extra blur was processed over the files / pixels. And the files produce artefacts. I don't see the artefacts in the testfiles of DPreview, but I did see them in downloadable files on the web. At 200 percent there is a certain pattern going on with artefact / blurred / broken pixels. I know this sounds like pixelpeeping, but I don't see it in any other raw files than the S95 files and I will see it in huge enlargements. In fact, the 100IS file currently is better than the S95 file. I'm curious to see what CHDK without badpixel removal will show. Will this really show the clean RAW data? That would be awesome. The camera is now at the dealer to check out (but he will probably not have a hunch of what we are talking about here.....) I'll try and see what CHDK without the badpixel removal will do. I like the S95 as a camera, but not it's files. If the CHDK RAW without the badpixel removal will be about the same as what I'm seeing now, I'll get rid of it.


Re: raw and nothing but raw sensor information
« Reply #4 on: 09 / August / 2011, 18:34:12 »
The S95 has a real aperture.
The Digital IXUS 100IS / Digital ELPH SD780 IS / IXY Digital 210 IS has an ND filter.

The issues you describe could be the result of diffraction caused by using a small aperture.  Without pictures (including the EXIF data), it is difficult to determine if this is the cause.  This cause would be consistent with seeing the problem in your own pictures but not in those done by DPreview.  DPreview is very likely to have selected, for most of their pictures, an aperture which would show little, or no, diffraction artifacts.

 

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Offline reyalp

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Re: raw and nothing but raw sensor information
« Reply #5 on: 10 / August / 2011, 00:13:24 »
I'll try and see what CHDK without the badpixel removal will do. I like the S95 as a camera, but not it's files. If the CHDK RAW without the badpixel removal will be about the same as what I'm seeing now, I'll get rid of it.
CHDK badpixel removal would only affect the pixels you (or the canon firmware, in the case of DNG badpixel.bin) have marked as bad. It won't affect the overall look of the rest of the image.

As keyman says, posting pictures would make it a lot easier to understand. The best way to do this would be putting full res DNGs on a file hosting service like box.net. A crop of a small area at 100% zoom + exposure data could work too.
Don't forget what the H stands for.

Re: raw and nothing but raw sensor information
« Reply #6 on: 10 / August / 2011, 03:02:52 »
Thanks Keyman and Realp,
Here I have a 200 percent zoom printscreen of the files: dpreview, dogfur and face. http://bartalexander.com/rawtojpeg200percentsharpened.jpg
I know zooming in to 200 percent isn't the same as interpolating to 200 percent, but in this way the difference is more clear. There is definitely a pattern going in the face, a pattern I have never seen before. The pattern consists of unsharp lines that affect the pixels / image quality. The pixels get mixed up as you can see in the dogfur. I know of diffraction influencing image quality, but I know that is not the case here. Using a Kodak 14n with no aa fliter, I know diffraction can even enhance image quality caused by moire in wide apertures. The shots in the sample were shot at wide open aperture. Apart from the mixed up pixels in the fur, that show at any size, the files printed until 11x13 inch look very good. But again, I'm after printing at 4 x 5 Ft, which I can do with the 100IS with no sacrafices.

Thanks guys,
Kind regards,
Bart

Re: raw and nothing but raw sensor information
« Reply #7 on: 10 / August / 2011, 06:07:58 »
I know of diffraction influencing image quality, but I know that is not the case here.
Nope, it is not.  

It appears to be an artifact of the algorithm you have chosen for demosaicing.  Most RAW converters will permit you to select from a variety of algorithms.  Which algorithm to select tends to be camera specific (some of the algorithms will look good, some will look like what you've got).  Sometimes it is something that you must select on an image by image basis.  Making this selection is a normal part of using RAW images.

For my A650IS I usually use VNG 4 color interpolation (vng4).  You should try all the ones available in the raw converter which you are using to see which works best for your camera.  If for some reason your RAW converter does not provide you with such options, there are a few free RAW converters which you could use.  I use UFRaw and RawTherapee.  Both have at least 5 different demosaicing algorithm options.

Demosaicing artifacts exist in both your picture and the ones which you have downloaded from dpreview in RAW format and converted yourself.  You should be able to clearly see the differences between the image you have created from the dpreview RAW file and the JPG format RAW conversion that dpreview did with Adobe Camera RAW (I assume).  The file you want to download for comparison is called: img_2248.acr.jpg   In order to download that file you will need to select your camera in one of the other small comparison windows; then select RAW format; at that point you can select to download the converted JPG version.  Attached you will find a 200% crop of the same area you used.  Two versions are attached: A) a ufraw and the VNG4 algorithm, and B) the dpreview converted RAW.  The one I did with ufraw could use some more/alternate processing to get to a final version (I would probably want to also try it with RawTherapee).  However, it should be good enough for demonstrating this issue.

As a suggestion, you might want to spend a considerable amount of time playing around with RAW converters.  There are a lot of optional processing parameters.

A page that compares a few demosaicing algorithms.
Google searches for more demosaicing comparison information: 1 2
« Last Edit: 10 / August / 2011, 12:18:38 by keyman »


Re: raw and nothing but raw sensor information
« Reply #8 on: 10 / August / 2011, 06:50:38 »
If this forum supported "Like" or "Upvote" or any other way to flag a great posting,  I'd nominate the previous post here for special status.  One of the better and more informative posts I've read in quite a while.

Thanks keyman !!
Ported :   A1200    SD940   G10    Powershot N    G16

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Offline whim

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Re: raw and nothing but raw sensor information
« Reply #9 on: 10 / August / 2011, 07:13:27 »
If this forum supported "Like" or "Upvote" or any other way to flag a great posting,  I'd nominate the previous post here for special status.  One of the better and more informative posts I've read in quite a while.

Thanks keyman !!


Couldn't agree more ... added to my forum links collection.  Thanks a lot, keyman.

wim

 

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