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"Flip Both" affects color in RAW8 mode

Posted: Tue Jan 22, 2019 1:00 am
by larryh
Hi Robin,
I was collecting images from the lunar eclipse last night and after a meridian flip I decided to use the "flip both" option to get the image oriented the same as before the meridian flip. Today I discovered that all of the images after I selected "flip both" did not debayer correctly in Planetary Image PreProcessor (PIPP). I normally use RGGB to debayer the RAW8 images, however, I found that the images were blue when I did so. Thankfully it turned out that if I used BGGR I got the correct color. Here is an example .png file along with the camera settings I used:
Moon_00040.png
Moon_00040.png (835.83 KiB) Viewed 661 times
Moon_00040.CameraSettings.txt
(715 Bytes) Downloaded 55 times
I don't know if there is any similar effect for other image formats or when selecting other flip options.
Thanks!
Larry

Re: "Flip Both" affects color in RAW8 mode

Posted: Tue Jan 22, 2019 8:01 am
by admin
Hi Larry,

that is as designed – when you turn the image round or flip it in either or both directions, the sequence of coloured pixels at the top left-hand corner changes. SharpCap tracks this internally when you flip the image and writes the correct value into the image meta data. Unfortunately not many Astro processing applications read the image meta data from fits files concerning the Bayer pattern, so it's necessary to make these changes manually when processing.

Think of the image pixel layout being like this and then imagine what it looks like when you flip it either upside down or upside down and horizontally.

Code: Select all

RGRGRGRGRG
GBGBGBGBGB
RGRGRGRGRG
GBGBGBGBGB

Cheers, Robin

Re: "Flip Both" affects color in RAW8 mode

Posted: Tue Jan 22, 2019 8:17 am
by turfpit
Well done Larry for working it out.

Take a simple 2x2 grid RGGB:

RG
GB

Flip it top to bottom gives:

GB
RG

Flip left to right:

BG
GR

Hence matrix becomes:

BGGR

For anyone meeting this for the first time see viewtopic.php?f=35&t=254
The doc that keeps on giving - > 3500 views and > 500 downloads.

Dave