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How to artificially change/increase the exposure of your image

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tim
GL Blogger

How to artificially change/increase the exposure of your image

Post#1 by tim » 16 Mar 2018, 22:41


If you shoot in RAW and have other photo editing software you can play with exposure.
But my cheap point and shoot camera only shoots in jpg (jpeg) so i don't have the option to play with exposure.

But I thought of a trick to artificially play with exposure.
I was thinking of long exposures. If my camera only does maximum 15 seconds exposures, I could take two 15 second shots and use addition mode to combine them. That would act similarly like how a 30 second exposure would look.

But what sucks about my camera is that after taking 15 second exposure it takes like 10 seconds or so to process the image before i could the next shot (so if subjects move within that break i'll get a weird break in between the motion blurs).

So then I thought I could use one 15 second shot but just use addition mode with itself. That would do the trick and that's how I found this trick.
Instructions:

1. <File>/Open your (underexposed) image.
2. <Layer>/Duplicate Layer, set the top layer's mode to Addition (This will most likely make it look like it's over exposed).
3. Then play with opacity of the top layer to taste (so that it's at an exposure that you like).

This method will work with Subtract mode to lower exposure as well (provided your image isn't super exposed/blown out).

This is very different from changing brightness, since brightness will make black pixels brighter too. This method will keep black black. With brightness settings you'll probably have to play with contrast to get the image to look good again. But this method (to me) simulates what exposure in RAW does since every pixel will only brighten proportionally based on how bright it already is.

Here are some sample edits using this trick:
Source images: Christopher MacDonald (my friend)
christopher_northern_lights_1_before_after_addition_mode_with_itself.jpg
christopher_northern_lights_1_before_after_addition_mode_with_itself.jpg # (29.81 KiB) Viewed 3458 times (Thumbnail | Recognize | Sq Tile)
christopher_northern_lights_2_before_after_addition_mode_of_itself.jpg
christopher_northern_lights_2_before_after_addition_mode_of_itself.jpg # (26 KiB) Viewed 3458 times (Thumbnail | Recognize | Sq Tile)
Here's a sample of mine, I prefer the after with a slightly more exposure:
car_panning_before_after_addition_mode_adjustment.jpg
car_panning_before_after_addition_mode_adjustment.jpg # (225.73 KiB) Viewed 3438 times (Thumbnail | Recognize | Sq Tile)
You can also use this trick with luminosity masks (especially to bring out dark shadows using the D layer) created by luminosity masks script
aka Tin

         

Pat625
Tutorial Creator

Post#2 by Pat625 » 17 Mar 2018, 03:05


Thanks for the information. I will try it on some photos that are too dark.

tim
GL Blogger

Post#3 by tim » 17 Mar 2018, 15:41


Hopefully you can share the before and after so we can all see what kind of improvement this method can do
aka Tin

         

Pat625
Tutorial Creator

Post#4 by Pat625 » 18 Mar 2018, 06:11


I took an old picture to try your method. I believe it is helpful but the picture has other problems that I could not fix, such as dark shadowing in one place which if try to correct makes it too bright elsewhere. Also a blown out too bright area at the back end of the white rat toy.
Tin Tran_Cat Before underexposure fix.jpg
Tin Tran_Cat Before underexposure fix.jpg # (411.41 KiB) Viewed 3348 times (Thumbnail | Recognize | Sq Tile)
Tin Tran_Cat after underexposure fix.jpg
Tin Tran_Cat after underexposure fix.jpg # (480.09 KiB) Viewed 3348 times (Thumbnail | Recognize | Sq Tile)
.

david
Forum Member

Post#5 by david » 18 Mar 2018, 10:09


Pat,

I had a quick try at improving your cat and mouse picture. If you look at the histogram I think you will see that it is not under-exposed - it just has extreme contrast. The burnt out area on the mouse is not possible to adjust. The darkest parts can be lightened but will show noise.
I just used one of my favourite Saul Goode Luminosity Masks - M - to modify the mid-range areas.

The method suggested by Tim may help to recover an otherwise unusable image, but at the cost of increasing noise. If however multiple exposures are combined noise will be reduced.

david.
Attachments
Tin Tran_Cat underexposure fix.jpg
Tin Tran_Cat underexposure fix.jpg # (490.07 KiB) Viewed 3336 times (Thumbnail | Recognize | Sq Tile)

Pat625
Tutorial Creator

Post#6 by Pat625 » 18 Mar 2018, 18:16


David, thank you very much for your knowledgeable comments. I have not really played with the luminosity masks. This I must practice. Thank you.

PhotoMaster
Global Moderator

Post#7 by PhotoMaster » 20 Mar 2018, 13:28


This is absolutely brilliant! I have never seen that done before. The result is amazing. Adjusting the opacity of the top layer allows you better control of the exposure without distorting the image!
Artists Aren't Crazy...
We're Eccentric!

neurolurker
Forum Member

Post#8 by neurolurker » 26 Oct 2018, 14:44


Late to the party. While trying this out I found that you can use the mouse wheel to scroll through the available modes instead of individually selecting and applying each mode as I had previously been doing. And that you can use a scrolling wheel to more easily change the values of the opacity settings instead of using the arrows in the opacity box. Perhaps this interface "secret" was only secret to me ... but thanks much. You never know where a tip might lead someone. And the original tip was very helpful as well!
GIMP Learn rocks...

Pat625
Tutorial Creator

Post#9 by Pat625 » 26 Oct 2018, 18:37


I did not know about the use of the mouse wheel to scroll through the available modes and opacity either. Which version are you using, 2.8 or 2.10 Gimp?

neurolurker
Forum Member

Post#10 by neurolurker » 27 Oct 2018, 01:31


Pat, I'm using Windows 10 and Gimp 2.10.6 on a Dell all-in-one desktop.
GIMP Learn rocks...


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