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Black pixel issue

Posted: Mon, 9th Aug 2010, 6:34pm

Post 1 of 8

StylishGirl10

Force: 100 | Joined: 9th Aug 2010 | Posts: 2

PhotoKey Lite User

Gold Member

For some reason all the images I have taken are having quality issues once I've uploaded them. The black pixels are very horrible.
Posted: Mon, 9th Aug 2010, 7:05pm

Post 2 of 8

Axeman

Force: 17995 | Joined: 20th Jan 2002 | Posts: 6124

VisionLab User VideoWrap User PhotoKey 5 Pro User MuzzlePlug User PowerPlug User PhotoKey 3 Plug-in User FXhome Movie Maker FXpreset Maker MacOS User

SuperUser

Hey, sorry to hear you are having difficulties. If you could provide a link to a sample image it would be very helpful. Troubleshooting image quality without seeing the image is very difficult. Also, some additional detail about what exactly is happening, and when, would be useful.

When you say uploaded, do you mean when you upload the exported PhotoKey images to the internet? Or do you mean when you import the images into PhotoKey? You describe the black pixels as horrible, but I'm not sure what you mean by horrible. Are they noisy? the wrong color? missing?
Posted: Tue, 10th Aug 2010, 6:36am

Post 3 of 8

fotoguydfw

Force: 1625 | Joined: 12th Mar 2010 | Posts: 2

Gold Member

I think I may know what you are talking about. We had it early on when we would take senior pictures and it was noticable with anything black. The black would look pixelated and slightly faded.


I'm not sure if this is the problem you are having or not - but going into the Key and changing removal from 100% to around 70ish% fixed it for us.
Posted: Tue, 10th Aug 2010, 5:34pm

Post 4 of 8

StylishGirl10

Force: 100 | Joined: 9th Aug 2010 | Posts: 2

PhotoKey Lite User

Gold Member

the black is distorted and in some images the correct colors aren't even showing up. I'm not sure if it's a software issue or what.
Posted: Thu, 12th Aug 2010, 7:46pm

Post 5 of 8

njush

Force: 1720 | Joined: 29th Jan 2010 | Posts: 46

PhotoKey 3 User Windows User MacOS User

Gold Member

This looks like a limitation of the keying engine.

Basically, the key is based on the difference between the background color channel (blue or green) and the other two channel values for any given pixel. This works well generally, but falls apart a bit for very dark/black pixels, since there is little to no difference between the channel values (in fact, the background channel can even have a slightly higher value that the non-background channels) ... which results in the mess you see in the "blacks".

Since we generally shoot with backgrounds that are evenly lit (and therefore have a fairly consistent luma value) a great solution for PK would be to include luma based cutoff sliders that could essentially designate low and high thresholds for the keying engine that would designate pixels brighter or darker than the slider values as being "solid".

Here's a link to where I've asked for this before in the wishlist thread:
http://fxhome.com/forums/viewtopic.php?t=39504&postdays=0&postorder=asc&start=23

In the meantime, you can work around the issue in photoshop.
Setup your PK project to be sized "As Foreground", so your export will be the same size as the original image. Key as normal in PK, export canvas to PNG with no background, this keys most of the image for you, but leaves some messiness in the darks of your subject.

In photoshop...
- Open your PNG.
- Also open your background image and drag it into your PNG window, then make sure the PNG layer is above the background layer.
- Now, we'll fix the blacks....
- Open your original photo and drag it into your PNG photo so it's the top layer above the PNG and the background.
- Go to the channels panel and select the channel that matches your backdrop (green channel for greenscreen, blue channel if bluescreen) ... you should now see just a grayscale image of your selected channel.
- Drag this channel to the "New Channel" icon at the bottom of the channels panel to make a copy.
- Now, use the Image->Adjustments->Levels command on the result to adjust the image so the bright and mid-grays are completely white, leaving just a tiny bit of gray edge around any black zones in the image.
- Use the Image->Adjustments->Invert command to invert the image so the black areas become white, and visa versa.
- Getting close .... now drag this layer that you've been adjusting down to the "Load Channel As Selection" icon (looks like a circle marquee) at the bottom of the channels panel. The black areas of your image should now be selected.
- Click the RGB channel at the top of the Channels panel to show the full color image again.
- Time to finish! ... go back to the Layers panel and make sure that top layer (with the original image) is selected. Click the Add Layer Mask button at the bottom of the layers panel.

The result should be that only the dark and black areas of your original image are left "solid", revealing the rest of the PK PNG and your background. If needed, you can do a bit of touch-up to the mask with a brush. You can also use the Hue/Sat command to desaturate backdrop color from your original image layer if needed in case some background color spilled in when you filled in the darks.

If you feel like posting a not-keyed-yet copy of your example above, I could try the process out on it for you.

Hope this helps.
Have fun.
Posted: Thu, 12th Aug 2010, 7:50pm

Post 6 of 8

Axeman

Force: 17995 | Joined: 20th Jan 2002 | Posts: 6124

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SuperUser

That just looks like the key settings need adjusted. How much have you messed with the settings?
Posted: Thu, 12th Aug 2010, 8:47pm

Post 7 of 8

njush

Force: 1720 | Joined: 29th Jan 2010 | Posts: 46

PhotoKey 3 User Windows User MacOS User

Gold Member

Axeman wrote:

That just looks like the key settings need adjusted. How much have you messed with the settings?
For what it's worth, I've run into the same challenge in a number of instances.
I have "messed with the settings" extensively, attempting to apply my experience in feature film vfx (primarily using Nuke) and teaching university VFX classes at the graduate and undergraduate level.

So far I haven't been able to work out how to appropriately address this particular issue solely within PK (which I love to use for photography since it's so easy, fast and effective for most of photography keying situations I work with), but the photoshop workaround helps fill the gap when faced with this, and it would be really cool to get some more controls and tools to be able to tweak more keying parameters directly inside PK.

Hope this helps.
Have fun.
Posted: Fri, 12th Nov 2010, 4:51pm

Post 8 of 8

Simon K Jones

Force: 27955 | Joined: 1st Jan 2002 | Posts: 11683

VisionLab User VideoWrap User PhotoKey 5 Pro User MuzzlePlug User PowerPlug User PhotoKey 3 Plug-in User FXhome Movie Maker FXpreset Maker Windows User

FXhome Team Member

Can either the OP or njush upload the original green screen images that are affected by this issue so that we can test them here?

Thanks!