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Thread: Please fix blending

  1. #1
    Join Date
    Apr 2012
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    299

    Please fix blending

    EDIT: Please note I have posted pictures illustrating this behavior below. Scroll down to see!

    Hi:

    I am having a hard time blending smooth gradients in oils without extreme saturation or color artifacts appearing. This occurs for both standard and "real colour" blending modes.

    Generally between two values of the SAME color, for example light grey turqoise and blackish turqoise, blending does not produce a set of colors with the value varying from blackish turqoise to light grey turquoise, instead bands of extreme blue (dark and highly saturated) appear in the middle of the gradient from nowhere.

    When I run the eye dropper accross the gradient it is clear that the color shifts in hue toward blue in the middle but at the ends is properly turquise. The saturation also shifts from relatively low at both ends to a greater value in the middle of the gradient.

    It would seem that blending two colors is not restrained to colors between them... but can go off in some strange direction in the color space. Normally blending processes "converge" as opposed to "diverge".

    Please fix the blending system... or add a blending option (above or under real color blending) which behaves in a nice bounded manner which converges to a color that makes sense (color constrained blending).


    thanks
    DO
    Last edited by DarkOwnt; 02-21-2013 at 06:59 AM.

  2. #2
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    Apr 2012
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    Is this oversaturation blending artifact fixed in version 4?

  3. #3
    Join Date
    Mar 2006
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    New Zealand
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    Trying what you're describing I'm seeing some minor hue shifting only which is probably due to the gamma protected blend which is designed to maintain the visual blend but may in some cases make things oversaturate slightly where the gamma curve boosts darker hues. It's also possible that the streaking occurs when one of these points is picked up on the head and re-blended in to the result. I'm not seeing huge variance when I try however.

    So, could you record a script that has an example in and send it to support@artrage.com and that should help us understand exactly what you mean.
    Matt
    ArtRage UI
    Ambient Design.

  4. #4
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    Apr 2012
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    Hello Matt:

    I just sent a script to the email address.

    Essentially starting with a single color of moderate saturation:

    Take a low (dark) value version and blend it with a high (light) value version of the same color, (each having a moderately low saturation), blending creates a third color which although "similar" has a very noticeably greater level of saturation. Essentially instead of interpolation between the two colors started with... the saturation gets overblown ... in a sense from out of nowhere.

    Blending "beyond" what you start with is very counterintuitive... I expect belnding to approach a limit... an asymptote... i.e. approach (converge to) the color I imagine to be "fully blended"... and blending ad infinitum should approach and stay there (convergence)! Here it actually diverges... the more blending the worse it can get (doing more would produce a script which would be too big.. but you understand so I didnt record for too long).

    I'd really love it if this could be tamed!!! Maybe a bounded, asymptotic, converging blending mode?




    Cheers
    DO
    Last edited by DarkOwnt; 02-12-2013 at 01:08 PM.

  5. #5
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    DO observations seems to be quite interesting. I sent DO a PM asking him to post a picture of his findings.
    This would be of help. I tried to reproduce the findings but... I don't have a control to compare.

  6. #6
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    I've taken a look at the script and I think I can see what you are referring to. Important note here - turn off With Lighting in the sampler before testing colours, otherwise you'll get shifts that are created by texture rather than actual colour.

    What I see is this: The vertical spread of the blend sticks at roughly the same hue. There is a maximum 2% shift in there at one specific point due to the saturation change which was probably created by the gamma adjustment. The saturation shift is caused by the same thing and it's primarily focused in one area where the paint was re-blended.

    This is the limitation of the digital system - When the brush head picks up paint, all the paint on the head becomes the colour that was just picked up. To avoid that we'd need to track multiple layers of colour on the brush head and the calculations become too demanding. This means that if you blend over an area that has a slight saturation shift due to the gamma correction, and blend that in to other paint, you'll see the shift become more obvious as the differently saturated paint blends in, changing the saturation of the paint on the canvas, and when that gets picked up it repeats the process.

    The script shows problems where there is heavy blending over a single spot and that's where the limitation of the system lies. Unfortunately, working in a limited colour space it's very hard to remove that kind of problem. Here, it doesn't appear particularly extreme, but if you continue to blend in from areas that have small issues the results can look worse.
    Matt
    ArtRage UI
    Ambient Design.

  7. #7
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    Hello Matt:

    Mathematically speaking given a set of input pixel color values (each having unique RGB or HSV triplet values) there is always one (or a set) of RGB or HSV triplet values which is an average of (or wholly inside the "gamut" of) the input RGB and HSV values. This is true regardless of the digital (descrete value) nature of the color information. If an algorithm is based on blending via averaging some or all pixel values in a careful manner where all the resulting values are an average (or inside the gamut) of the input, there should be no divergence. I understand creating a blending system to work like this is a choice...but it is not impossible or outside the limits of computation.


    That said, I understand there are performance considerations and trade-offs. For speed (on cheap systems) and gamma correction perhaps, ArtRage has given up precision and convergence. This is one choice that can be made by software developers and will depend on many factors such as the desired look, responsiveness, and particular customer base (and how good thier computer systems are).

    I own Corel Painter 12.2.1. It has no such blending problems. I assume Adobe Photoshop CS6 also has no such blending problems as I've not heard of complaints about its blending system either.

    Currently I have to do my blending in Painter 12.2.1 and then to get the kind of painterly effects I want, I import (or trace) with ArtRage. I would prefer to use ArtRage on its own. Over the past 5 years Painter has become increasingly unreliable (buggy) and frustrating. I like ArtRage very much. I want to love it.


    Supposing that the current blending system of ArtRage is not flawed, and does not need to be fixed, i.e. it simply uses a blending system which for reasons chosen by the developers, is "different", I would like as an option that someday another blending mode which perfroms to the level of Painter and Photoshop be added. One which converges to a value or values within the gamut of the input values.


    Once again please look at this as a "feature" request and understand it will help your product to compete with the big boys.


    cheers
    DO

  8. #8
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    Apr 2012
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    Hello Matt:

    Just bought v4. Really impressed.

    Out of curiousity you spoke of gamma adjustment a few times. How is this involved in blending? Does it have something to do with color management profiles? Is there a way to avoid its use or cause its effect to reduce?

    cheers
    DO

  9. #9
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    Quote Originally Posted by Lima View Post
    DO observations seems to be quite interesting. I sent DO a PM asking him to post a picture of his findings.
    This would be of help. I tried to reproduce the findings but... I don't have a control to compare.
    Dear Lima:

    Here are some samples for your inspection.

    The goal here was to blend adjacent patches into a smooth transition/gradient. This was done both with ArtRage and Corel Painter 12. Percentages definining the original color patches are in HSV. There are three blended gradients in each image.

    1. Dark Unsaturated Cyan (33% S, 20% V) Patch - Light Unsaturated Cyan (33% S, 80% V) Patch
    2. Black (0% S, 0% V) Patch - Med Unsaturated Red (33% S, 50% V) Patch - White (0% S, 100% V) Patch
    3. Med Unsaturated Green (33% S, 50% V) Patch - Light Grey (0% S, 80% V) Patch

    These were blended in ArtRage using standard paint blending palette knife:
    Click image for larger version. 

Name:	ArtRageBlend.jpg 
Views:	157 
Size:	109.0 KB 
ID:	73368





    These were blended in COREL PAINTER 12 using standard paint blending palette knife
    Click image for larger version. 

Name:	PainterBlends.jpg 
Views:	208 
Size:	38.2 KB 
ID:	73369


    As far as I know Corel Painter uses a blending method/system which is computationally possible - and which deals with the same digital constraints and discrete color values that ArtRage is "limited" by.




    What's your honest opinion Lima?



    Anyone else? Am I being picky? Please pipe up or nothing will get done.


    Cheers
    DO

  10. #10
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    Apr 2012
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    Anyone else want to weigh in on the blending system?

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