Post Reply 

Not sure if this is even possible

Apr 15, 2011, 18:18
Post: #1
Not sure if this is even possible
I am trying to isolate koi for the front page of my koi club newsletter. Most of the koi are photographed on a blue background because it makes the colors stand out better and it is complementary to the orange that is most common in this fish. The problem is that when I am working with a white or light colored fish, the blue bleeds into the light colors, particularly in the fins, so I end up with fish that are blue on the edges.

I am not a graphics artist and in no way an expert on gimp and I haven't found any filters or methods that might help me figure this out.

This is the original picture
   

This is how I butchered it.
   

You can see how the blue has infiltrated deeply into the white. This fish has brilliant white that needs to show up and I'm really hoping there is a filter or something I can use to make it happen. If anyone can help me, I would greatly appreciate it.
Find all posts by this user
Quote this message in a reply
Apr 15, 2011, 19:51
Post: #2
RE: Not sure if this is even possible
One thing I have to say, is the edges are a little Alliased, sorry no idea how to fix your color troubles, but have you read any tutorials on rendering?

The best method to render with is using Paths, and carefully selecting around your object, this gives a very clean edge, if done with a high quality image, are you planning on using these images at the size they are? Bigger? Smaller?

And only a guess on the blue, maybe some sort of Colorizing to removed the Blue?
Best of Luck,
Willy
Visit this user's website Find all posts by this user
Quote this message in a reply
Apr 15, 2011, 21:26
Post: #3
RE: Not sure if this is even possible
Not impossible... To understand how it works, a little bit of explanation:

If you look at Gimp standard color dialog, you can see R,G,B sliders, but also another triplet labelled H,S,V, for Hue, Saturation, and Value. Hue is a basic color:; red, green... saturation is how little white in contains (any hue with 0 saturation has no real color) and Value is brightness.

If you decompose an image into these three components, the Value "channel" is the monochrome image, where most of the detail is. The "Hue" channel often has large uniform areas for all the parts that come from the same can of paint. For instance on a car the body has a uniform hue so the Hue channel would display a very flat shape. The "Saturation" channel is black where the colors are desaturated. An interesting consequence of this is that as long as you don't modify the "Value" channel, you don't lose detail. The

Now, back to your fish... your fish is not white, it's blue, with varying saturation, it is more saturated where it shows as blue, and less so where the fish appears white. So removing the blue is actually more like de-saturating it.

One solution is to use Colors>Decompose, choose HSV, that produces an image with the three corresponding layers, and then work on the saturation layer (darkening the fins...) and then recompose. You can do the "decompose" part once as a curiosity, to understand this HSV thing, but there is a more efficient way.

This efficient way uses a specific "mode" of the paint tools: "saturation". In that mode, the paint tools only transfer the saturation part of the color to the layer. So, if we pick a color with little saturation, painting the fins with it will remove the blue. Hence: use the color picker to pick color where the fish is almost white, set the paintbrush with a fuzzy brush, put it in saturation mode, and paint over the blue parts. The fun thing is that you don't even need to be very careful about spills, except on the very colored spots (I made a mark in the middle of the biggest spot).

[attachment=295]

For the fun, by using a brush in "Hue" mode, that only transfers the hue component, you can produce a new species:

[attachment=296]

One last word: the fins and tails get a bit gray, because working with HSV often changes the perceived lightness of the result. You may want to do some fuzzy selects in that area and add lightness and contrast... but there you'll be working on the "Value" component and you can lose detail quickly, so beware.

Now answering your questions on
https://Gimp-Forum.net
Visit this user's website Find all posts by this user
Quote this message in a reply
Apr 16, 2011, 03:25
Post: #4
RE: Not sure if this is even possible
Willy, I've struggled with that, but I'll read some tutorials on rendering and see if I can do a nicer job of it.

Ofnuts, Thank you for the explanation! I'm going to have to break it down and just work with it until I fully understand exactly what I'm doing and how it's happening. I've seen those control panels, but I had no real understanding of them. Typically I tried moving a slider all the way one direction to see if it got close to what I wanted, and when it didn't, I abandoned that altogether. I really wish I could say I was on the right track, but I was way off track.

Thanks again!
Find all posts by this user
Quote this message in a reply
Apr 16, 2011, 08:07
Post: #5
RE: Not sure if this is even possible
Once again, thank you for the help. I just got done using paths to take the fish out of the background and the saturation brush to take all the blue out of the fish and make it look great -- or at least as great as I can make it right now. Actually doing it was really fast, so I'm not just pleased, but amazed. In case you are interested, this particular fish has been nominated for the AKCA Young Champion from our club. It will compete against fish from all over the country.

DrCreosote
Find all posts by this user
Quote this message in a reply
Apr 16, 2011, 13:57
Post: #6
RE: Not sure if this is even possible
That is a very cool acomplishment Big Grin

Do we get to see your finished Product?

Best Wishes in the Competition,
Willy
Visit this user's website Find all posts by this user
Quote this message in a reply
Post Reply 


Forum Jump:


GIMP ForumPortalArchiveContactTermsRSS