SX40, SX 50 vignetting, flat frames etc - page 2 - RAW Shooting and Processing - CHDK Forum

SX40, SX 50 vignetting, flat frames etc

  • 16 Replies
Re: SX40, SX 50 vignetting, flat frames etc
« Reply #10 on: 13 / November / 2013, 16:09:40 »
The Rawtherapee support for flat frames looks very promising.
That should be able to completely correct vignetting and without the nasty banding produced by some other methods.

It seems I have to capture a raw flat-field image first and the correction is performed on the raw linear data at the beginning of the processing 'pipeline'.

Re: SX40, SX 50 vignetting, flat frames etc
« Reply #11 on: 14 / November / 2013, 06:06:18 »
Thanks to blackhole and dvip for suggesting  (as separate items) flat-frames and Rawtherapee.

The combination works perfectly, unlike commercial software at any price.

The correction is applied even before the demosaicing stage.

The first five images have produced a 13,000 pixel wide panorama.
The final panorama will be 260,000 pixels wide.

Of course, you cannot render that as a single image.
« Last Edit: 14 / November / 2013, 07:51:06 by Microfunguy »

Re: SX40, SX 50 vignetting, flat frames etc
« Reply #12 on: 19 / November / 2013, 19:12:46 »

As no SX50hs users have responded as to whether that camera has significant vignetting   ... I decided to buy one.

And that is just as bad if not worse.

The problem can be solved if I use raw (at last) and a flat frame.

Today I was observing something  that to the naked eye is just a tiny white blob behind a hill.
At the SX50hs 1200mm focal length, in the image you see the dish of the Jodrell Bank radio telescope 50 Km (30 miles) away.
Not just the dish but the gimbal supports the dish rotates between !

Re: SX40, SX 50 vignetting, flat frames etc
« Reply #13 on: 26 / December / 2013, 10:21:52 »
I just wanted to add that there's correction for this in DxO Optics Pro 9.1, and there's a fully functional free trial for it.  It seems to work well for me.  There's also software which can view very large sized images.  Do a search for gigapixel images, you'll find a few articles discussing how they were done.  I believe autopano and some other software supports this, even Picasa I think.

My worst problem in these images is air turbulence.  I tested a target at 700m and there's a large amount of waviness to the image, which changes quicker than 1/240s at least.  Lines never look straight.  I used astronomy software to fix this, but it means taking a lot of photos per segment.
« Last Edit: 26 / December / 2013, 10:27:00 by jmac698 »

Re: SX40, SX 50 vignetting, flat frames etc
« Reply #14 on: 26 / December / 2013, 16:01:06 »
I did further research, as I knew something was wrong here - it seemed to me that a good panoramic stitcher should be able to deduce vignetting automatically.  Well here it is:

That is the manual chapter which explains the settings for vignetting correction in Hugin, a free panoramic stitcher program, available at


Offline dvip

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Re: SX40, SX 50 vignetting, flat frames etc
« Reply #15 on: 08 / January / 2014, 00:14:08 »

Here is some information from the RT manual (


Noise Reduction
RawTherapee’s  powerful  Noise  Reduction  tool  lets  you  eliminate  noise  while
retaining detail. It uses wavelets and a Fourier transform to work its magic. As with
all tools in the Details tab, to see the effects you must zoom in to 100% (1:1) or

To find the best set of Noise Reduction values for your image:

1. Check the sharpening tools to make sure that you’re not sharpening any fine
detail, because your noisy photo has no fine detail! All they would do is
amplify the noise. If you’re using Contrast by Detail Levels to give the image
more depth, make sure that the first 0 (Finest)slider is turned off.

2. Zoom into the photo to 100% and find an area that has both sharp in-focus
parts as well as large plain out-of-focus ones, so that you can prevent noise
reduction from destroying details as you tweak it.

3. Start by setting the Luminance Detailslider to 0,

4. Increase the Luminanceslider until the luminance noise has been smoothed

5. Because luminance noise is all gone now (though we haven’t recovered any
detail  yet),  this  is  a  good  time  to  denoise  the  color  channels.  Increase
Chrominance (Master)to a level where chrominance noise is gone but color
detail in small objects hasn’t been lost. You can reduce or boost the effects of
noise reduction on the red and blue channels by respectively lowering or
raising the  Delta Chrominance Red/Bluesliders. In most cases 0 should be

6. Now  increase  the  Luminance Detail slider  to recover  detail until  you are
happy with the noise:detail trade-off.


Regarding colors, it is very subjective... I don't like the green I get from these cameras so I lower the green channel from 100% to 98%.  If you want Canon colors adjust the color channels and compare with the colors that you get from your jpg. Save your profile (PP3) so you can re-use it. You can save colors, noise reduction, lens distortion, WB, vignetting correction, etc...

BTW, there is a new RT beta version with better Noise  Reduction:

I hope this helps.

Re: SX40, SX 50 vignetting, flat frames etc
« Reply #16 on: 08 / January / 2014, 08:01:49 »
I hope this helps.

many thanks for that and your personal messages.

Since our last discussion, I have read the entire Manual a couple of times.

For my specialised panoramas taken at 1200mm f.l. the flat frames feature 'saved the day'.
Without it, the images would be unusable.

In future, I will use Canon raw to get better colours and lens correction without much work.



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