08-25-2021, 07:20 PM (This post was last modified: 08-25-2021, 07:20 PM by Mango Turtl.)
I've noticed that on some images, specific parts of the image will occasionally become black and grainy when the Hue-Saturation feature is used. Is there any fix for this? Does anyone know what causes it? I've tested a little bit, and it seems that the black artifacts always appear, no matter what I do with the Hue-Saturation feature.
In the first attached image, I have not used Hue-Saturation yet. Some areas of the coral are naturally in shadow, but still have a color that makes sense and looks pretty good. In the second attached image, I tried to use Hue-Saturation to remove some green tint from the image. It worked, but left some areas of the coral that were previously in shadow with a black, grainy look.
The Blue channel is essentially 0 in that area (due to a previous processing step?). Since most color operationz act like multiplication, it will remain 0 whatever these operations do elsewhere. So when the intensity in the Red/Green channel is reduced this will reduce the difference between Red/Green and Blue, and so move the result towards dark greys.
(08-25-2021, 07:40 PM)Ofnuts Wrote: The Blue channel is essentially 0 in that area (due to a previous processing step?). Since most color operationz act like multiplication, it will remain 0 whatever these operations do elsewhere. So when the intensity in the Red/Green channel is reduced this will reduce the difference between Red/Green and Blue, and so move the result towards dark greys.
Any fix you can think of other than just...adding back some blue, I guess? What's weird to me is that those black areas don't just pop up when I start using the Hue-Saturation feature...they pop up as soon as the Hue-Saturation menu even opens, before I've even picked a hue to modify.
HArd to suggest a fix since there are many blown out areas. Plus I assume this is just a part of a bigger picture (possibly not even the main subject) and the effect on the rest of the picture of anything I try should be ascertained.
(08-26-2021, 04:14 AM)PixLab Wrote: Did you try playing with the "Overlap" (before starting the settings)?
That didn't seem to work, unfortunately. I worked around the problem on the first pic by doing a second white balance along with some other settings...but unfortunately I'm now stuck on a second photo where I can't seem to get out the cyan without those artifacts appearing...
It happens on both the Color Balance and Hue-Saturation tools, and it happens as soon as I open the tool before I even change anything...so it seems like a bug to me, maybe. I'm not sure.
08-26-2021, 12:45 PM (This post was last modified: 08-26-2021, 01:18 PM by PixLab.)
Ok, underwater images have a very particular way to be processed (no Hue-saturation!!!), if you're a diver you know that after 5 meters, no more red, after 10 meters no more yellow and all in between with red, and so on depending the sun light.
Having said that to get a proper white balance you can try Colors > Auto > White balance, some time GIMP does a good job with it... (but it add too much contrast, but it can be surprisingly good)
But to be sure, here is how I do it manually:
On the original image > Color Picker tool > take something that YOU KNOW is gray (or white, but white might be blown out...), not dark grey, but middle/light grey
Then New layer (transparent) > fill it with that color (which is blue-ish or green-ish depending where you did dive or the depth you dove) > put it in Mode "Divide" (play with transpency ~50%)
If you are not very satisfied, duplicate that layer (the blue-green-ish one) then > Color > Invert > put it in mode "Dodge" > play with opacity ~50%
(don't forget to untick the eye / visibility of that blue-green-ish layer below)
If you are not satisfied, yet... > play opacity with both colored layers ~30%
once you satified
Then right click on a layer > New from visible > play the light/shadow with the curves or the levels (and ONLY now you can use Hue saturation if you wish)
(08-26-2021, 12:45 PM)PixLab Wrote: On the original image > Color Picker tool > take something that YOU KNOW is gray (or white, but white might be blown out...), not dark grey, but middle/light grey
Then New layer (transparent) > fill it with that color (which is blue-ish or green-ish depending where you did dive or the depth you dove) > put it in Mode "Divide" (play with transpency ~50%)
If you are not very satisfied, duplicate that layer (the blue-green-ish one) then > Color > Invert > put it in mode "Dodge" > play with opacity ~50%
(don't forget to untick the eye / visibility of that blue-green-ish layer below)
Thank you! It's my first time trying to use any semblance of a professional-looking program to edit my photos; they were turning out pretty good but this should make them even better! Funnily enough though, after using your method of white balancing...I still got more of those black-ish grainy spots all over the place if I tried to use Hue-Saturation to boost the saturation of a certain color after using the new layer from visible. I guess it's just something I'll have to live with for now.
08-26-2021, 05:26 PM (This post was last modified: 08-26-2021, 05:27 PM by rich2005.)
I do not think it is a bug, as ofnuts wrote there is no blue in the image. Not unknown with underwater images to be missing a colour.
There is an old gimp script for initial corrections, it is a white balance set up for underwater. This description from the script.
---------
; DESCRIPTION
;; This script acts as a red fitler on diving photos.
;; To launch it, goto the menu <Image>/Script-Fu/Enhance/Diving red filter
;;
;; Basically, create a new layer containing the corrected picture
;; You can adjust the red level (sometimes, green might works better !)
;; and set if the white balance has to be performed... --------
script attached: unzip put in C:\Users\"yourname"\AppData\Roaming\GIMP\2.10\scripts
Also not a bad idea to up the precision prior to any editing, it might help Image -> Precision say 32 bit floating and linear.
A very quick view of that as an animation. https://i.imgur.com/O0FCNNC.mp4 that also shows a sample point used for color info.
(08-26-2021, 03:12 PM)Mango Turtl Wrote: I still got more of those black-ish grainy spots all over the place if I tried to use Hue-Saturation to boost the saturation of a certain color after using the new layer from visible. I guess it's just something I'll have to live with for now.
Um.. no you don't have to live with, if this method does not work, try the ofnuts's red filter that rich2005 is speaking about,
Out of curiosity, is your camera a DSLR?
