Hello,
Sometimes I experience issues with visible light beams in renders. Does anyone know why this happens and how to fix it?
They are hard to notice from a distance, but become clearly visible when zoomed in or printed on a large format
If I look at Photoshop and check the values the RGB values are indeed moving around the red lines from:
24/24/24
23/23/23
22/22/22
21/21/21
etc.
Gradients like this are hard to prevent since a normal RGB image just doesn’t have any options in between those values.
I’ve originally a printing background and such images can indeed be quite a pain to get right in print. I’m not sure if you manually convert the images to CMYK for print since that at least would give you most control. I think the issue is more noticeable in digital print than in offset as well since the offset raster will also distract you from the gradient, like a dithered image.
If you haven’t tried, you could also try to render a 32-bit image like EXR/TIF/PSD which has way more values than an 8-bit RGB. Converting those to a CMYK for print could give a much better result.
Another trick is to add a bit of noise in those area’s. That will obfuscate the shape because you won’t get one single line where it jumps from one value to another.
Not really a one solution fits all images I’m afraid. If you want I can take a look at a high res image you rendered or if you’re able to share the scene I can try what would give the best result in this case.
I would guess that this is kind of a ground reflection.
Just check the lighting settings. Else global illumination is not necessary.
thank you,
I indeed found that it is an RGB issue. I removed the background light and added a radial gradient in Photoshop. This didn’t solve the issue.
I will try rendering in 32-bit!
The noise trick also works well most of the time. What I often did was create a layer in the Photoshop document using uniform monochromatic noise (just a low value) and put the layer blend mode on darken for example.
And it depends a bit on the CMYK conversion but if the background is build up from C/Y/M/K I think you won’t see it in print. If the background basically will only use the black ink you will notice it more. If you are also generating the certified PDF you can display the separate ink plates in Acrobat and check if it’s still noticeable.
If it will be some newspaper advertisement I wouldn’t worry too much as well since that paper will make it all appear just black since ink will flow more with such paper.
I’ll drop this link in here since I think it might be relevant to you. I wrote an article on color banding: https://www.willgibbons.com/color-banding/
it will be printed very large, for the wall of an office. about 7m by 4 meters…
Do you think this will exaggerate the effect?
I don’t think so because it’s a kind of background and people focus on other things. That’s basically also why for a magazine advertisement they want 300dpi but for a background they are happy with 150dpi most of the time.
You can just add some notes for the people who will print it and ask them to check if it will cause any issues. They know their printers best and often have their own tricks to solve things like this.
A bigger challenge might be the amount of black. Black consists of all 4 inks most of the time and there’s often a max amount of ink the paper can carry/absorb. But if you tell them you worry about it and you don’t want to end up with one black big piece of wallpaper in the end they can also take a look at that.
Maybe they will make the entire image a bit lighter and maybe add a bit extra light on the object to have the best result. Has also to do with the kind of papier.
For example a newspaper black/white add may only have around 85% black if you want to print a black square. Because of the paper that will show as a solid black. If you actually would do 100% black ink for a larger surface it stays wet and stamps across all pages.
And while a PDF profile can also consider it your image is pretty subtle so it’s good if there’s a human actually checking it at the print company. Most of the time they love such questions since such things make their work interesting. And if they fail or are not happy with the result they just print another with different settings.
Not sure if you already have a certain company for printing but else I can ask an ex-colleague of mine if he has some suggestions. He get loads of such prints done for the main Dutch bicycle brands showroom stuff.