A Gimp trick, is this just a long way to do a simple adjustment?

**GUB** · 10-28-2018, 08:20 PM

I bumped into this while doing some editing. It seems to have different qualities to just changing contrast or saturation.
Take an image , duplicate it , color white to alpha and paste onto original.

The original whites seem to darken a little and the colours boost but don't seem to try and flood the channel.
Could be a nice tonal treatment in B&W
Can anyone point me to an article about the trick?
Same image one colour before and after, one b&w before and after.

Attached Images

View Picture EXIF

View Picture EXIF

**GUB** · 10-28-2018, 08:27 PM

And ; (yes a little heavy handed here but look at the translucency)

**jbinpg** · 10-28-2018, 09:40 PM

In Gimp, setting alpha to white means you make all pixels in that layer opaque. Does this result in an overall darkening when you paste the duplicated image onto the original? This seems to be the case judging by your posted images. Perhaps studying here would be worthwhile:

Chapter*8.*Combining Images

Jack

**GUB** · 10-28-2018, 09:56 PM

Originally posted by jbinpg

In Gimp, setting alpha to white means you make all pixels in that layer opaque. Does this result in an overall darkening when you paste the duplicated image onto the original? This seems to be the case judging by your posted images. Perhaps studying here would be worthwhile:

Chapter*8.*Combining Images

Jack

Thanks for that link - it is going to take more than a quick skim to absorb it though.

Originally posted by jbinpg

In Gimp, setting alpha to white means you make all pixels in that layer opaque

Na what I did was color (white) to alpha in the color menu. And the result is a little darker but I wouldn't call it an overall darkening - more like a contrast boost with a bit of added saturation chucked in. I suspect it is something like (in 8 bit units) say a pixel at 70 60 50 becomes 20 10 0 with colour to alpha and because of the transparency the result becomes 90 70 50 when pasted. Does that make sense?

**jbinpg** · 10-29-2018, 12:07 AM

Ah, sorry, I misread the original post. This link provides some clues to the result you see, I think:

How to make a color transparent in Gimp | alvinalexander.com

Jack

EdoNork · 10-29-2018, 01:12 AM - **1 Like**

You can try changing the threshold from pure white to "near" white when converting to ALpha, so the high lights are not darkened.

**GUB** · 10-29-2018, 02:02 AM

I am using 2.10 and I think what you mean may be the opacity threshold. I pulled it back about 10% for the last image and still got a boost but much more subtle. This night shot is an archive one I had edited as best I could. applied this trick to it and just amazed at the boost - especially in the flowerbed.

Attached Images

**GUB** · 10-29-2018, 02:03 AM

Originally posted by EdoNork

You can try changing the threshold from pure white to "near" white when converting to ALpha, so the high lights are not darkened.

Does that mean you use this technique?

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
21st century film photography ... simple and not simple	Kupepe	Film Processing, Scanning, and Darkroom	27	06-28-2018 01:19 AM
FA 28-70 f/4 Minimum FL 31mm--A "Simple" Adjustment?	dms	Repairs and Warranty Service	2	12-24-2016 10:21 PM
Neat little trick I just saw on YT.	pathdoc	Film Processing, Scanning, and Darkroom	3	04-27-2016 07:26 AM
All lens needs AF fine adjustment, does the camera need a global adjustment? Thanks	bennyxyz	Troubleshooting and Beginner Help	9	04-21-2016 12:36 PM
GIMP 2.6.12 vs. GIMP 2.8.0	Vasyl	Digital Processing, Software, and Printing	13	06-19-2012 02:00 PM

10-28-2018, 09:40 PM	#3
jbinpg Site Supporter Join Date: Mar 2008 Location: Prince George, BC Photos: Gallery \| Albums Posts: 3,546	In Gimp, setting alpha to white means you make all pixels in that layer opaque. Does this result in an overall darkening when you paste the duplicated image onto the original? This seems to be the case judging by your posted images. Perhaps studying here would be worthwhile: Chapter8.Combining Images Jack

10-28-2018, 09:56 PM	#4
GUB Loyal Site Supporter Join Date: Aug 2012 Location: Wanganui Photos: Gallery \| Albums Posts: 5,760 Original Poster	Originally posted by jbinpg In Gimp, setting alpha to white means you make all pixels in that layer opaque. Does this result in an overall darkening when you paste the duplicated image onto the original? This seems to be the case judging by your posted images. Perhaps studying here would be worthwhile: Chapter8.Combining Images Jack Thanks for that link - it is going to take more than a quick skim to absorb it though. Originally posted by jbinpg In Gimp, setting alpha to white means you make all pixels in that layer opaque Na what I did was color (white) to alpha in the color menu. And the result is a little darker but I wouldn't call it an overall darkening - more like a contrast boost with a bit of added saturation chucked in. I suspect it is something like (in 8 bit units) say a pixel at 70 60 50 becomes 20 10 0 with colour to alpha and because of the transparency the result becomes 90 70 50 when pasted. Does that make sense?

10-29-2018, 12:07 AM	#5
jbinpg Site Supporter Join Date: Mar 2008 Location: Prince George, BC Photos: Gallery \| Albums Posts: 3,546	Ah, sorry, I misread the original post. This link provides some clues to the result you see, I think: How to make a color transparent in Gimp \| alvinalexander.com Jack

10-29-2018, 01:12 AM - 1 Like	#6
EdoNork New Member Join Date: Mar 2012 Posts: 12	You can try changing the threshold from pure white to "near" white when converting to ALpha, so the high lights are not darkened.

10-29-2018, 02:02 AM	#7
GUB Loyal Site Supporter Join Date: Aug 2012 Location: Wanganui Photos: Gallery \| Albums Posts: 5,760 Original Poster	I am using 2.10 and I think what you mean may be the opacity threshold. I pulled it back about 10% for the last image and still got a boost but much more subtle. This night shot is an archive one I had edited as best I could. applied this trick to it and just amazed at the boost - especially in the flowerbed. Attached Images

10-29-2018, 02:03 AM	#8
GUB Loyal Site Supporter Join Date: Aug 2012 Location: Wanganui Photos: Gallery \| Albums Posts: 5,760 Original Poster	Originally posted by EdoNork You can try changing the threshold from pure white to "near" white when converting to ALpha, so the high lights are not darkened. Does that mean you use this technique?