DSLR HotPixel removal

[Cleon_Wells]

I think I've got it figured out, maybe.

[Simon Hicks]

If this is true, i.e. that a single hotpixel creates a group of four hotpixels automatically after the debayer, then is this a signature of a hotpixel in a debayered image, i.e. any group of exactly four pixels that are all significantly higher than their surrounding pixels? And if so, can we design a filter to only select out these groups of four pixels and replace them with their neighbouring values?

[Cleon_Wells]

Simon, I think the problem with your idea would be recognizing the extra four pixels that surround the actual HotPixel. The extra pixels created by the DeBayer process are around 25% of the actual HotPixel ADU level.
Cleon

[Cleon_Wells]

And if anyone would like an explanation how the DeBayer magic happens.
Craig Stark has a great article here.
http://www.stark-labs.com/craig/articles/assets/Debayering_API.pdf
Cleon

[Philip de Louraille]

I'd think you'd want to remove the hot pixels before debayering. Less noise that way.

[Cleon_Wells]

Philip, yes you have to remove the HotPixel before the Debayer process or you will get a four leaf clover.
Cleon

[Cleon_Wells]

I acquired 36 usable test subs of ngc2244 last night and used PI Integration with Winsorized Sigma Clipping and mount alignment errors to remove the HotPixels plus the Debayer artifacts. The HotPixels have ADU levels of 1.0 and the four surrounding Debayer artifacts have ADU levels of 0.25.
Cleon

[Alejandro Tombolini]

And if anyone would like an explanation how the DeBayer magic happens.
Craig Stark has a great article here.
http://www.stark-labs.com/craig/articles/assets/Debayering_API.pdf
Cleon

Hi Cleon, thank you for sharing this article.
I didn't know how the debayer process was working. I wonder which of all these methods is the one that is called Super Pixel in our BatchDeBayer tool

Hola Cleon, gracias por compartir éste artículo.
No sabía como trabajaba el proceso de debayerizado. Me pregunto cuál de estos métodos es el que se llama Super Pixel en nuestra herramienta para debayerizado (BatchDeBayer).

Saludos, Alejandro. 

[Cleon_Wells]

Alejandro, I’m glad Craig’s article helped you understand the DeBayer process. The process takes a Bayer matrix, ((which is created by placing a Color Filter Array (cfa) RGGB filter in front of each set of four pixels of the Camera’s monochrome CCD chip)) and creates four color pixels from four monochrome pixels. The sampling of 4 pixel levels, the four adjacent pixels next to this pixel,(nearest neighbor)  sets the color for the created pixel. I think this is Bilinear decoding, RGGB.
When you look at one of my Debayered HotPixels, note that the four pixels (the four leaf clover) connected to the HotPixel are being created by the DeBayer process, seeing one bright green pixel and three dark pixels (group of four) next to the pixel that is being created. These four created phantom pixels (the clover leaf) have a ADU level of 0.25 while the HotPixel in the middle has a ADU level of 1.0.

         A SuperPixel file can also be created with the BatchFormatConversion script and is 1/2 the pixel size of the original file, using the four RGBG pixels to create one pixel, but is not Debayered, this file can be Debayered. This gets very confusing..check this Web site out.....

http://www.licha.de/astro_article_ccd_camera_bayer_matrix.php

BatchFormatConversion uses settings from the Format Explorer tab and in the case of the DSLR_RAW files, uses settings in the RAW Format Preferences window to create the new file format.
When you Calibrate a DSLR raw file a FormatConversion happens and the conversion uses Raw Format Preference settings.
I hope this simplistic explanation helps, I still think there's some magic involved. LOL
Cleon