Retinex color operation
I'd like to Discuss Retinex. I decided to do it here before submitting a bug report.
In theory the retinex operation is very useful in fixing badly lit images. In practice, I've had little success with it. So I decided to fiddle around with it. My test picture was a chinese temple on a background of blue sky. usually you want to just brighten up some darker areas or bring detail in an area that's too brightly lit, without changing the rest of the image. In my test case, The sky's color was ruined when retinex was applied and most of the well-lit areas lost most of their color.
I'll break down what happened:
1. The properties that can be changed by the sliders in the retinex dialog are not clear at all. The documentation doesn't explain the first two in terms understandable to a non-mathematician. Whatever it is they are doing, they are not helping in correcting images.
2. The result is too strong. I find I have to do a "fade" every time I use it. My suggestion: add a multiplier slider that would do an internal fade. The default should be about 0.5.
3. The algorithm is indiscriminate: it is used to fix bad lighting but it also works on well-lit areas. I believe it should have less effect on pixels (or areas) whose average luminosity value is 0.5, and more effect on pixels with values closer to 0 or 1.
I managed to achieve a selective retinex using the following method: 1. copy the layer 2. paste into quick mask 3. blur the mask using gaussian blur (8.0 radius) 4. invert the colors (only if you want to affect just the darker areas) 5. use levels or contrast to mask out the mid values 6. Perform Retinex
The above procedure can probably be turned into an integral part of retinex so that retinex only works on those parts. Perhaps adding another slider that controls the luminosity / strength ratio.
Photoshop's "lighting/shadow" algorithm has two sliders. One for choosing the strength of the effect on lighter parts of the image, and one for choosing the strength of the effect on darker parts of the image. This seems like a desirable thing to have.
Comments?
2012/4/24 Michael Grosberg <grosberg.michael@...400...>:
Comments?
Yes, one: Does this message belong here? This is list is for inkscape and afaik we don't have quick masks :-p
I guess you were trying to reach GIMP dev list. In that case you have my support, what you're saying makes sense and would improve the filter, which is pretty useless in its current form.
Cheers, Gez.
Did you try the new Lightness Filter in Inkscape 0.48 devel ? It's has three sliders : one for lights, a second for shadows and a third for global lightness. It's based on Component Transfer "Gamma"
ivan
________________________________ De : Michael Grosberg <grosberg.michael@...400...> À : inkscape-devel@lists.sourceforge.net Envoyé le : Mardi 24 avril 2012 22h19 Objet : [Inkscape-devel] Retinex color operation
I'd like to Discuss Retinex. I decided to do it here before submitting a bug report.
In theory the retinex operation is very useful in fixing badly lit images. In practice, I've had little success with it. So I decided to fiddle around with it. My test picture was a chinese temple on a background of blue sky. usually you want to just brighten up some darker areas or bring detail in an area that's too brightly lit, without changing the rest of the image. In my test case, The sky's color was ruined when retinex was applied and most of the well-lit areas lost most of their color.
I'll break down what happened:
1. The properties that can be changed by the sliders in the retinex dialog are not clear at all. The documentation doesn't explain the first two in terms understandable to a non-mathematician. Whatever it is they are doing, they are not helping in correcting images.
2. The result is too strong. I find I have to do a "fade" every time I use it. My suggestion: add a multiplier slider that would do an internal fade. The default should be about 0.5.
3. The algorithm is indiscriminate: it is used to fix bad lighting but it also works on well-lit areas. I believe it should have less effect on pixels (or areas) whose average luminosity value is 0.5, and more effect on pixels with values closer to 0 or 1.
I managed to achieve a selective retinex using the following method: 1. copy the layer 2. paste into quick mask 3. blur the mask using gaussian blur (8.0 radius) 4. invert the colors (only if you want to affect just the darker areas) 5. use levels or contrast to mask out the mid values 6. Perform Retinex
The above procedure can probably be turned into an integral part of retinex so that retinex only works on those parts. Perhaps adding another slider that controls the luminosity / strength ratio.
Photoshop's "lighting/shadow" algorithm has two sliders. One for choosing the strength of the effect on lighter parts of the image, and one for choosing the strength of the effect on darker parts of the image. This seems like a desirable thing to have.
Comments?
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Of course I mean Filters/Color/Lightness !
ivan
----- Mail transféré ----- De : Ivan Louette <ivan_louette@...48...> À : Michael Grosberg <grosberg.michael@...400...>; "inkscape-devel@...1794...s.sourceforge.net" inkscape-devel@lists.sourceforge.net Envoyé le : Mardi 24 avril 2012 23h20 Objet : [Inkscape-devel] Re : Retinex color operation
Did you try the new Lightness Filter in Inkscape 0.48 devel ? It's has three sliders : one for lights, a second for shadows and a third for global lightness. It's based on Component Transfer "Gamma"
ivan
________________________________ De : Michael Grosberg <grosberg.michael@...400...> À : inkscape-devel@lists.sourceforge.net Envoyé le : Mardi 24 avril 2012 22h19 Objet : [Inkscape-devel] Retinex color operation
I'd like to Discuss Retinex. I decided to do it here before submitting a bug report.
In theory the retinex operation is very useful in fixing badly lit images. In practice, I've had little success with it. So I decided to fiddle around with it. My test picture was a chinese temple on a background of blue sky. usually you want to just brighten up some darker areas or bring detail in an area that's too brightly lit, without changing the rest of the image. In my test case, The sky's color was ruined when retinex was applied and most of the well-lit areas lost most of their color.
I'll break down what happened:
1. The properties that can be changed by the sliders in the retinex dialog are not clear at all. The documentation doesn't explain the first two in terms understandable to a non-mathematician. Whatever it is they are doing, they are not helping in correcting images.
2. The result is too strong. I find I have to do a "fade" every time I use it. My suggestion: add a multiplier slider that would do an internal fade. The default should be about 0.5.
3. The algorithm is indiscriminate: it is used to fix bad lighting but it also works on well-lit areas. I believe it should have less effect on pixels (or areas) whose average luminosity value is 0.5, and more effect on pixels with values closer to 0 or 1.
I managed to achieve a selective retinex using the following method: 1. copy the layer 2. paste into quick mask 3. blur the mask using gaussian blur (8.0 radius) 4. invert the colors (only if you want to affect just the darker areas) 5. use levels or contrast to mask out the mid values 6. Perform Retinex
The above procedure can probably be turned into an integral part of retinex so that retinex only works on those parts. Perhaps adding another slider that controls the luminosity / strength ratio.
Photoshop's "lighting/shadow" algorithm has two sliders. One for choosing the strength of the effect on lighter parts of the image, and one for choosing the strength of the effect on darker parts of the image. This seems like a desirable thing to have.
Comments?
------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Inkscape-devel mailing list Inkscape-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/inkscape-devel
------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Inkscape-devel mailing list Inkscape-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/inkscape-devel
participants (3)
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gespertino＠...400... -
Ivan Louette -
Michael Grosberg