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Old 02-06-2018, 07:23 PM   #1
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Default Video Processor = RGB White Balance / Colour Grading

This is my first post here.
I was trying to find a way to get Reaper Video Processor FX to do some basic colour grading of R G B levels, mostly for subtle tweaks to white balance.

My Canon camera (with Magic Lantern) is capable of getting very good results if I carefully adjust colour temperature in Kelvin manually before I film something, but too often the case, it's not fine-tuned ideally because I was in a hurry to set up, or the lighting conditions were poor or changed during a long shoot, so it sometimes needs minor correction afterwards.

Anyway, I couldn't find any factory preset in Video Processor that did that job directly, so I adapted a little script and came up with this, which I thought I'd share...

//RGB White Balance Colour Grading
//@param2:red 'red' 0 -0.1 0.1
//@param4:green 'green' 0 -0.1 0.1
//@param6:blue 'blue' 0 -0.1 0.1
//@param8:intensity 'intensity' 1 0 10
input_info(src,w,h) ? ( project_w=w; project_h=h; ); // preserve input dimensions
w>0 ? gfx_blit(src);
gfx_mode=w>0 ? 1 : 0;
gfx_gradrect(0,0,project_w,project_h, red, green, blue, intensity);
This seems to work okay for subtle adjustments of R G B white balance. The "intensity" dial lets you turn down to zero (bypass) to compare your original image. Turning up past default 1 goes beyond normal everyday range into special effects range.

I wondered if this is useful to anybody like me struggling to do basic video edits in Reaper, but moreover, I wonder if anyone far more experienced than me can make a better job of this type of thing, using more flexible parameters in the script, etc.

I know proper "Colour Grading" software offers full control over highlights / midtones / shadows separately, and can be applied to specific areas of the image also, and can be changed dynamically over the timeline, which is all very complex and complicated to attempt in Reaper. I wonder if duplicating the video item on another track(s) and using opacity to see through several video layers with different processing for each layer could mimic highlights, midtones and shadow processing somehow?
Any other ideas how to make R G B colour grading possible or more flexible in Reaper?

Last edited by propianist; 02-06-2018 at 07:35 PM.
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Old 02-06-2018, 08:57 PM   #2
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Posts: 5,537

not bad! really useful actually. I have something similar in my presets. great start.

btw a negative number for intensity can be cool useful here too.

Edit - should say it's not really white balance, but more like tint or using colored filters.
if RGB are the same and you add or subtract (below 0) alpha it's like a brightness control.
REAPER Video Tutorials, Tips & Tricks and more at The REAPER Blog

Last edited by EpicSounds; 02-06-2018 at 09:06 PM.
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Old 10-06-2018, 07:35 AM   #3
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thanks alot, this is exaclty what i was looking for!
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Old 11-03-2018, 06:13 AM   #4
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Many thanks.
A great addition to the video processor presets.
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