Noise in Raw Files

[Nodrog]

Very impressed by Affinity Photo, and one of the attractions was the ability to deal with RAW files.

 

I have a Canon Powershot SX30is which does not natively produce RAW files, but with CHDK firmware it will save as DNG.

 

When I import these into Affinity (or view them in Faststone), they have a large amount of noise which seems to to be like the descriptions of stuck pixels. Jpgs created in camera at the same time are clear of noise.  

 

 I am able to clear the coloured pixels fairly well by setting Luminance and Colours to around 90% in the Noise Reduction panel, but this leaves smaller black pixels - lots of them!

 

 

 

I have read up on dead pixels and hot pixels but these shots were around 1/30th of a second.

 

Any ideas would be very welcome!

 

Thanks

[Lee D]

Hi Nodrog,

Welcome to the forums.

From what I can find the CHDK firmware DNG files do seem to suffer from bad pixels when the files are checked in various apps. I don't think the JPEG processing has been changed so they shouldn't suffer from the same issue. I've never installed anything but the manufacturers firmware updates, for me these are ones to use as they have been designed for the model they're being installed on.

[Nodrog]

Thanks Lee.

 

I would have happily stuck with the Canon firmware but it does not include RAW output.

 

I'll play a bit, but given the current quality of the DNG output I think I might need to stick to working with jpgs. 

[XzavieR]

First off, apologies for gravedigging this thread, but I hope I have something useful to add.

I also run CHDK in my Canon compacts, and I'm very happy with it. I was also happily surprised to see that Affinity has support for lens correction for many CHDK cameras out of the box, something which Adobe Lightroom and Photoshop does not.

I have also seen the black pixel problem on many of my CHDK DNGs when processed in Affinity, but I don't see the same problem when processing the same files in Lightroom. I'm not sure if this issue would occur on a Mac as well, where Affinity can use Apple's RAW processing.

If CHDK is set to save DNG version 1.3 files, all bad pixels will be saved with a value of 0, and a DNG opcode will tell compatible software that a value of 0 is to be considered "bad". This saves some processing in the camera and makes saving DNGs faster (and you don't need to create a badpixel.bin map), since CHDK doesn't have to do anything with bad pixels except mark them as bad. Compatible raw processing software will interpolate these bad pixels from surrounding good pixels to obtain an approximate value. Affinity apparently does not (yet) support these opcodes so it doesn't know that it should interpolate the value of these pixels. It just uses the raw value from the DNG file without question, hence the black pixels.

You can work around this by setting CHDK to save DNG version 1.1 files instead. This makes CHDK not use DNG opcodes, but you need to generate a badpixel.bin to use as a map of bad pixels. This might take a few attempts. With this setting, the value of any bad pixel will be interpolated by CHDK in-camera while saving the DNG. So it takes more time to save a DNG, but it won't have the black pixel problem.

Hope this helps. And I also hope that Affinity will add support for interpolating bad pixels according to DNG opcodes in the future.