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  1. #316
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    Hi guys, my post from yesterday seems to have vanished permanently, but anyway I seem to have managed to get my email notifications working again. It's great to see so much activity here, but by far the most important thing I can say is to repeat what I said to Mr J on the last page:

    Quote Originally Posted by briggsy@ashtons View Post
    Make sure you do plenty of observation of actual objects in different situations to develop a sense of how the theory works in practice, such as as how strong to make the various component reflections contributing to the appearance. You'll learn much faster if you let nature answer your questions.
    I think you could improve a lot of your efforts and answer a lot of your own questions by taking the trouble to create suitable setups to compare them with what you expected, and perhaps photograph them and analyse the colour relationships in Photoshop. This will do you much more good in the long run than getting answers from someone else.

    If you are trying to paint simple objects from imagination make sure you actually understand the theory properly, for example with regard to the position of the highlight on a sphere (it has to be on a line from the light source through the middle of the sphere, not off to one side) and the importance of shading series.

    Siphonophores: I hope you can see that due to your decisions regarding the colouring, you've made your spheres look highly translucent, which I don't think was your intention. Also, to show strong sunlight on an opaque object requires a strong contrast between the light and shadow sides. Did you examine a coloured sphere in sunlight when doing the exercise?

    For the exercise of painting spheres into a photograph, I'd like to draw attention to this post, also on the last page:
    http://www.conceptart.org/forums/sho...20#post3653620

    In my attempt at one of Mr J's photos below, I first painted a white sphere under the lighting I inferred on the left, and then a coloured version on the right, using the procedure set out in that post. To follow this procedure, it is essential that you closely examine your photograph for clues that tell you about the relative strength and colour of the different light sources. I've marked in some of the clues I found useful for this into the photo, but I want you to see if you can follow for yourselves how I used this information.
    Attached Images Attached Images  


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  3. #317
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    Quote Originally Posted by briggsy@ashtons View Post
    Hi guys, my post from yesterday seems to have vanished permanently, but anyway I seem to have managed to get my email notifications working again. It's great to see so much activity here, but by far the most important thing I can say is to repeat what I said to Mr J on the last page:



    I think you could improve a lot of your efforts and answer a lot of your own questions by taking the trouble to create suitable setups to compare them with what you expected, and perhaps photograph them and analyse the colour relationships in Photoshop. This will do you much more good in the long run than getting answers from someone else.
    hey david, thanks a lot for taking the time once again. i do alot of observations and lately painting from live too, but some stuff i want to understand, not just taking for granted and use this for my paintings. probably i am something like a nerd on this, but so far my understanding on things really helped me in my own work. ive made myself simple rules to paint whatever i want, i can tell how water looks if its clean, turbid, when the sky is this and that bababa... but now it seems that ive got a big misunderstanding when it comes to reflectance of materials and i just try to solve it with knowledge, so please dont take it amiss that i ask further on this topic:

    you've noted the rgb distribution on my screenshot, it has a lot of color, very bright, the left ball, even in your version has less RGB color in sunlight than the sky has to offer, so why should it get darker in the shadows? i solved alot with just observation without asking anybody, but i am running at a wall with this.

    is it just because sunlight penetrates the material more than the skylight or something?

    if there is no answer to this i probably should rely more on the values than RGB-Distributions and create my shadows first of all on this information (sky value compared to white/sunlight) and alter the local-value at this factor.


    Edit: Probably i got a Solution, Needs some validation, but i am optimistic
    Last edited by Mister Janchichan; January 5th, 2014 at 06:54 PM.

  4. #318
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    Briggs: Thanks! I did not see that at all. I really struggled with trying to increase the contrast. I couldnt find many refs for direct sunlight in fact one i saw was a tennis ball which might explain the translucency thing. I will keep experimenting and seeing how to do this

    Edit: i think i wanted a little translucency but not as much as i had there.

    MJ. Im not sure i understand completely what u mean but i will try answer. Also Great job on those balls the yellow one to me really looks like direct sunlight.

    Ok so I think you are on the right track. There is less light hitting those areas of the sphere. Also the reflected light due to the ANGLE, is less powerful (45% of the original intensity) keeping in mind that it is already reflected and therefore much weaker than the original lightsource that i think might explain it.

    Also you can figure out the values in the rgb slider using linrans method tho personally i prefer the triangle thing.

  5. #319
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    Quote Originally Posted by Mister Janchichan View Post
    hey david, thanks a lot for taking the time once again. i do alot of observations and lately painting from live too, but some stuff i want to understand, not just taking for granted and use this for my paintings. probably i am something like a nerd on this, but so far my understanding on things really helped me in my own work. ive made myself simple rules to paint whatever i want, i can tell how water looks if its clean, turbid, when the sky is this and that bababa... but now it seems that ive got a big misunderstanding when it comes to reflectance of materials and i just try to solve it with knowledge, so please dont take it amiss that i ask further on this topic:
    I think it's really great that you want to understand things, and of course I'm not advocating the ignorant "just paint from life" rubbish that infected ca.org over the last few years (I mean in the free forums, not in the paid courses of course). It's just that it often seems to me that you go to the other extreme. For example, if you have a go at predicting what the shaded side of a white tower would look like, why not take the next step of taking a white cylinder outside and looking at it?

    Quote Originally Posted by Mister Janchichan View Post
    you've noted the rgb distribution on my screenshot, it has a lot of color, very bright, the left ball, even in your version has less RGB color in sunlight than the sky has to offer, so why should it get darker in the shadows? i solved alot with just observation without asking anybody, but i am running at a wall with this.

    is it just because sunlight penetrates the material more than the skylight or something?

    if there is no answer to this i probably should rely more on the values than RGB-Distributions and create my shadows first of all on this information (sky value compared to white/sunlight) and alter the local-value at this factor.


    Edit: Probably i got a Solution, Needs some validation, but i am optimistic
    Always remember that you are painting colour relationships. If you have a sphere under an ambient skylight and a concentrated spotlight, the colour you use to paint the skylit side depends on how bright the spot light is. The brighter the spotlight is, the darker you need to paint the skylit side to get the contrast - the relationship - right. So you end up having to organize your painting so that the lightest and brightest things are within the range of paint, and then paint everything else dark enough that the relationships to those lightest and brightest things are working.

  6. #320
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    Quote Originally Posted by Siphonophores View Post
    Briggs: Thanks! I did not see that at all. I really struggled with trying to increase the contrast. I couldnt find many refs for direct sunlight in fact one i saw was a tennis ball which might explain the translucency thing. I will keep experimenting and seeing how to do this .
    You really couldn't find a coloured ball?! (And I don't mean a picture of one on Google!). Or couldn't you find direct sunlight?

  7. #321
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    Its been a long time since ive seen the sun.... It forgot these lands, went south for the winter

  8. #322
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    Quote Originally Posted by Siphonophores View Post
    Its been a long time since ive seen the sun.... It forgot these lands, went south for the winter
    Fair enough, then. This is what it looks like:

    Name:  direct-sunlight.jpg
Views: 650
Size:  51.4 KB

  9. #323
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    i slightly changed how i establish my colors based on the last talk. if i want to paint something under very colored light i first have to paint the locals compared on white to better think of how it would change after colored light, but i am sure after some time i am able get more confidence.

    here are 2 of my latest little results

    Name:  rf34.jpg
Views: 661
Size:  38.8 KB
    Name:  dsdasd.jpg
Views: 655
Size:  16.2 KB

    even if those sphere-studies are fun im looking forward to paint something more vauleable finally

    edit: oops, didnt realise how small they are

    as mentioned i compare the colors to whire first, thought it would be a nice excercise like i did here, no multiplymode or such:

    Name:  24242.jpg
Views: 695
Size:  290.2 KB
    Last edited by Mister Janchichan; January 6th, 2014 at 06:51 AM.

  10. #324
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    brigggs: Thanks! changed my approach on this now heh. time to go back to it

    MJ: 1st one looks excellent! very representative

  11. #325
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    Ok so I tried to take what was said on board and came up with these. Now the first bunch were done before the crits were given so they are off. hopefully i got closer with the second batch. Then the third batch was a little light adjust to simulate that burning retina feel.

    Edit: they were posted in the wrong order. No 1 is the burning retina.
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  12. #326
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    So i was wondering, i was reading about the eye and specifically in regards to its ability to compress brightness in order to adjust the image.

    Would you know how much they adjust the brightness for different times of the day like sunrise and sunset etc?


    Heres what I found out so far.

    There is a Logarithmic relationship between luminance and subjective brightness perception in the human eye.

    Human eye uses a low pass filter and the band pass filter to compress the illuminance coming into the eye.

    The fall off for light compression is halved every time the frequency doubles.
    it can also divides 1/4 every time between the frequency doubles.

    But how does the frequency apply to the amount of light in the eye? Is the frequency the amount of light in the eye?

    From what i understood i thought there may be a significant decrease in the amount of compression that happens in low light circumstances.

    thanks again

    Edit: FOund the info i was looking for.
    Last edited by Siphonophores; January 12th, 2014 at 08:18 PM.

  13. #327
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    New question,

    How does the principle of uniform saturation account for the brezold brucke shift? Does it account for the abney effect? and if it doesnt how could we incorporate this?

  14. #328
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    Mister Janichan,

    The striped sphere in white light looks really good, but your method only seems to be letting you paint setups where the main light and the shadow illumination are the same colour. The way I showed lets you show multiple light sources of different colours.

    Siphonophores,

    Great, those last blocks look a lot more convincing than the spheres. One thing to at least be aware of though is that the gamut of digital colours is quite differently shaped to the range of commonly occurring natural colours, and extends well beyond the latter for many hues, especially in the greens and in the red-magenta-deep blue range (not so much in the yellows and greenish blues). So unless you tone down some colours below the maximum brightness and saturation possible, they'll tend to look a bit unnatural or even fluorescent (as in your green and magenta blocks).

    Quote Originally Posted by Siphonophores View Post
    New question,

    How does the principle of uniform saturation account for the brezold brucke shift? Does it account for the abney effect? and if it doesnt how could we incorporate this?
    My guess is that you'll get the same perceptual hue shift (if any) in the series of RGB colours of a given [I]digital[/I] "Hue" (H) and saturation as you would get in a series of colours of the same chromaticity in nature; in other words I think you'd automatically get the same hue shift happening.

  15. #329
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    thanks! yea this is definetly something to consider, I was thinking about it but i wanted to keep the high saturations in to simulate artificial colors and surfaces.

    Now i read somewhere that a way to compensate for it could be to select your shading series in a kind of curve rather than a linear selection. The one question i had after reading your post was,

    If the shift happens naturally would it only happen if your computer monitor was in Direct sunlight or is it a property of the Intensity of the light itself?


    So say we select a color with 100 brightness (which i think equals 1000 Lux) Will this because of its intensity automatically create the brezold brucke effect, or is this only effect of the high (v high) intensity of Direct sunlight?

  16. #330
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    Sorry, I haven't really gone into the BB effect in great detail myself because to be honest it seems a rather arcane issue in the context of practical painting. There's even some debate over whether the effect exists at all in object colours, as opposed to lights. I just meant that within the range of brightness of RGB colours, if there is any BB effect then I assume you would get that automatically as colours of a particular "Hue" and "Saturation" got brighter. If what you are concerned about is how to depict the BB shift of a light that gets brighter than that (?), then yes presumably you would have to adjust the hue appropriately. Any BB effect would of course be overprinted and possibly swamped by a difference in colour of the illumination between the shadow and light areas.

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