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Thread: "Export of Channels" feature

  1. #1
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    "Export of Channels" feature

    Hello,

    I'm a newbie user of ArtRage, but rather an old duck in computer graphics, more on the technical side than on the artistic one (actually I'm an faculty senior researcher in computer graphics) even if I've always found digital media very cool even for unskilled users like me. My first impression is that ArtRage is a totally-bluffing-you-can't-do-better perfect blend between a very realistic natural media simulation program and an unbelievable ergonomic user interface. Excellent job, you guys !!! Even if there are only few tools available yet, I consider that the software already outperforms Corel Painter, both on the ergonomics (well, that's not too hard to achieve ) and on the simulation quality.

    In the feature list of ArtRage 2.5, there is an unofficial one called "Export of Channels". I've tried it and I consider that it is a potentially extremely interesting tool, as it clearly exposes the underlying magic of ArtRage and should allow outstanding special effects on the resulting image. However, I've got a bunch of questions about the feature:

    * Is there an equivalent "Import of Channels" feature? I would like to test the effect of some tweaking of individual channels and blend them together in ArtRage.

    * While the role of the color, the bumpiness and the reflectivity channels are quite intuitive, I am not so sure about the shininess. Any hint on that point?

    * I don't think that exporting the individual channels on PNG files is the easiest way to use them (ok, I know... the feature is unofficial so I should not be too demanding). Why not propose a "Split channels as a layer group" and "Merge channels", which would offer straightforward manipulations within the program.

    Well, that's my two cents on the question...

    Scirocco

  2. #2
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    Hi Scirocco
    I hate to sound like a complete DoDo, but what are channels?? Could you explain them in terms I might undestand.. I do Photoshop a bit, and hear about channels with that software as well, but have no earthly idea what they are talking about.. Thanks
    Click Upper Right To Visit My Gallery

  3. #3
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    Hi Rick,

    Let's go for a short tutorial on computer graphics...

    In digital imaging, each pixel that belongs to an image, is composed of one or several channels. Each channel is usually encoded by a single byte (which means that the values encoded by each channel range from 0 to 255) althought some formats provide higher precision (mainly for high dynamic range pictures).

    For instance, a grayscale image is usually composed of 1 channel (the gray channel, also called the luminance channel) which expresses the brightness of each individual pixel, from black (=0) to white (=255). For a color image, there are usually three or four channels, depending on the color model. The most classical one is RGB, which is the native format of ArtRage, but you also have HLS, HSV, CIE XYZ, YUV, LAB, CMYK.

    Most image processing softwares allow the user to work with multiple layers, so they use an additional channel for each pixel, called alpha channel, that represents the transparency of the pixel. So each pixel for each layer is actually encoded by 4 bytes, this explains why images stored in multilayer formats, such as PSD or PTG, require much larger files than single layer formats, such as PNG.

    In digital painting softwares, each pixel contains several additional information: for instance, the thickness of the virtual paint, the reflectance or the shininess that characterize the way the media interact with light. These parameters are then used during a so-called "rendering step" which tries to simulate the look-and-feel of the real media. Even if the process is easy to explain, it is really difficult to provide a realistic appearance, and the Rage band has performed an amazing job here. Moreover, for each different tool and/or media, it requires a totally different mathematical model as the underlying physical process involved in real painting may be totally different. Watercolor is undoubtedly one of the most difficult media to simulate, because of its complicated interaction with the paper.

    So all these additional parameters used by the rendering step are stored in additional channels by ArtRage, one value per parameter per pixel per layer. The "export channels" feature of ArtRage 2.5 offers to visualize these channels by generating a grayscale image for channel (bumpiness, reflectivity, shininess). One can imagine working directly on these channels, in the same way as one can usually interact with the alpha channel to control transparency.

    This is a very exciting possibility, and it would be really great if the Rage band would provide us some feedback on that point.

    Well, that was definitely not a short answer, hope it helps though...
    Scirocco

  4. #4
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    Re: "Export of Channels" feature

    Quote Originally Posted by scirocco
    * Is there an equivalent "Import of Channels" feature? I would like to test the effect of some tweaking of individual channels and blend them together in ArtRage.

    * While the role of the color, the bumpiness and the reflectivity channels are quite intuitive, I am not so sure about the shininess. Any hint on that point?
    There currently isnt an 'import' channels feature. The 'Export' channels feature is VERY unofficial and therefore very restrictive, but doesn't need any UI. Importing channels would require some UI - especially with Bump attenuation.

    The Shininess channel is reall a 'Specular Intensity' channel. Some materials, such as oil, have high specular highlight intensity. Other material, such as chalk have very low specular intensity.
    AndyRage's mantra for graphics engine code:
    "Sure - how hard can it be?"

  5. #5
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    Re: "Export of Channels" feature

    Quote Originally Posted by AndyRage
    There currently isnt an 'import' channels feature. The 'Export' channels feature is VERY unofficial and therefore very restrictive, but doesn't need any UI. Importing channels would require some UI - especially with Bump attenuation.
    Ooooh, that's very bad news. I agree that a UI to tweak these parameters having the same high level of ergonomics as your other tools would be difficult to achieve. On the other hand, exposing the alpha channel and allowing direct painting on it has become quite standard in digital painting software. OK, it is unnatural compared to real life tools, but it provides much more precision and freedom that the poor old rubber tool. Many digital artists are now very fluent with alpha painting. I don't think that direct painting on the bumpiness or the shininess channel would be so difficult to understand. Actually it would be much more intuitive than, for instance, the ugly 25 blending modes of PhotoShop, which are almost totally unpredictible, even if you understand the underlying math equations.

    Quote Originally Posted by AndyRage
    The Shininess channel is reall a 'Specular Intensity' channel. Some materials, such as oil, have high specular highlight intensity. Other material, such as chalk have very low specular intensity.
    OK, I expected something like that. Let me know if I'm right in my guess: your paint model is actually implemented as a kind of Phong illumination model. The standard color being the diffuse color (or more exactly the ambient term as it's the only color that stays there when we switch off the light), whereas the "metallic" paint adds a specular term, composed of a "reflectivity" representing the ratio metallic vs. non-metallic, and a "shininess" representing the intensity of the specular term. Is this correct?

    Just to come back with the "Import channels" feature. Actually, I'm not afraid of writing a standalone piece of code that would blend the (tweaked) channel pictures into a single PTG file, Do you have some documentation describing the PTG format that you are willing to share with the rest of the world? That would really be great...

    By the way, do you intend to offer some kind of SDK with a future release of ArtRage? Even if the software is more tuned towards artist users, I guess that there would be interesting contributions from some (I've got a bunch of master students around me that would be delighted to write a couple of plugins).

    Regards,
    Scirocco

  6. #6
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    Wow!! Thats probably a whole lot more information than I need.. I'm 70 years old, and my mind can get cloudy real quick.. Think I will just have to go along my merry way and even though I work with a conciderable amount of layes in each painting, I probably don't need to understand exactly what is going on.. Thanks a bunch, for taking the time to answer my guestion..
    Click Upper Right To Visit My Gallery

  7. #7
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    Quote Originally Posted by Rick
    Thanks a bunch, for taking the time to answer my guestion..
    You're welcome, Rick. Sometimes the teacher that sleeps in me wakes up without control

    By the way, I totally agree with you: nobody really needs to know how everything works. For instance, I drive my car everyday and I am still unable to identify the carburator within all the mess that I find under the hood

  8. #8
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    Re: "Export of Channels" feature

    Quote Originally Posted by scirocco
    Just to come back with the "Import channels" feature. Actually, I'm not afraid of writing a standalone piece of code that would blend the (tweaked) channel pictures into a single PTG file, Do you have some documentation describing the PTG format that you are willing to share with the rest of the world? That would really be great...
    Would be *really* great ! Please...

    Scirocco

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