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Keying with Red/Pink tool costume (sample included)

Posted: Wed, 21st Jul 2010, 12:23am

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Dave Oleary

Force: 425 | Joined: 2nd Feb 2010 | Posts: 5

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I've used PK3 pro on thousands of school type photos. The problem is when the costume is red or pink tool (fine net like fabric). The PK3 does not key out just the green, it leaves the fabric unkeyed - where there should be a degree of transparancy.

photo loaded at:
http://www.daveolearyphoto.com/photos/941841887_jT29w-X3.jpg

These same outfits in blue or others key just fine, but the red & pink is problem. Although the sample uploaded here is a jpg, we always key on tiff or PNG files.

Thanks

dave
Posted: Wed, 21st Jul 2010, 8:50am

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Simon K Jones

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Do you have a higher resolution original image we can test - perhaps the original PNG or TIFF? If you could also provide an example of the blue fabric that works that would be useful for comparison.

Thanks!
Posted: Thu, 22nd Jul 2010, 11:45pm

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MarkD

Force: 900 | Joined: 12th Nov 2009 | Posts: 7

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Did you try a blue screen? I played with this sample in Photoshop, blending modes, saturation etc. in attempts to better prepare the image for keying....no luck. The semi-transparent areas turn grey. Painting over the material with a soft brush in "overlay" mode might work but terribly time consuming.
I have other ideas to try and i'll see what happens.
Posted: Fri, 23rd Jul 2010, 4:39pm

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Dave Oleary

Force: 425 | Joined: 2nd Feb 2010 | Posts: 5

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OK - I've uploaded several files for your download. There are three high rez with model in front of green screen. Then there are the three "after" composites. Two of the samples worked fine. The third is a train wreck.

On did not shoot the red dress in front of a blue screen - only the green screen. I went to the blue screen when the costumes were primarily green - but that's not the problem here.

The following url is an archive (zip) file on my mobile me account. The link is good for 30 days... although I need to deliver product by next week:-)

http://files.me.com/mrsnaps/wxe6s2

dave oleary
Snaps Productions
619-934-3434
Posted: Sun, 25th Jul 2010, 1:11am

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MarkD

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I will play with this. Options include swapping the green color for a blue color ( magic wand and other selection tools in Photoshop) and trying the blue key. Or may have to clone the dress and make the entire area solid ( omitting the translucent areas of the dress) Or you can also erase away the gray areas and introduce motion blur to the dress and hands aka a pirouette move. Man, this is a perplexing problem here!
Posted: Sun, 25th Jul 2010, 3:57pm

Post 6 of 13

MarkD

Force: 900 | Joined: 12th Nov 2009 | Posts: 7

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I came up with a compromised solution and I'll send you a message. I can send samples through your e-mail address as I don't know how to attach pics here.
Posted: Sun, 25th Jul 2010, 10:30pm

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njush

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Interesting example you have Dave.

Assuming PhotoKey is using a difference keyer, it won't key areas where the background channel (in this case green) has a value less than one of the other channels. In your example, there are several areas where the red channel value is well over the green value, even in transparent areas, so those pixels will key as "solid"

The main issue in your photo is that you've basically under-exposed the green screen. In your 8bit attachment, the green values are reporting in around 149, which is just over mid way up the scale which ranges to 255.

You can address this during you shoot by adding more light to the greenscreen so the values are over 200 when measured in an 8bit image.

For photos like this that you've already shot, you can give PK a helping hand by selectively boosting the green channel. Here's one approach....
Open the image in PhotoShop and access the "Channels" panel.
Select the RED channel only and click the "Load Channel As Selection" button (looks like a circle marquee tool at the bottom of the channels panel)
Now choose "Inverse" from the Selection menu.
What you've done so far is select all the pixels where the Red channel value has mid-to-low values ... perfect, because this is where we want to boost the greens.
Now click on the GREEN channel in the channels box.
Press Cmd+L on the Mac (or Ctrl+L on a PC) to open the Levels dialog. Drag the high point (small white triangle closes to the "preview" checkbox) to the left until the value below it reads about 190 for this example.
Click OK.
Click the RGB channel to view your photo in full color again.
What you should see is a much brighter greenscreen.
Save this out as a JPG for PK and run a key in PK ... should work much better.

Hope this helps.
Have fun.

Note to FXHome programmers....
Would be a great enhancement for PK if we could selectively deactivate a channel (or better still, have a multiplier slider/knob with a zero->1 range) for keying calculations.

Last edited Mon, 26th Jul 2010, 2:37pm; edited 1 times in total.

Posted: Mon, 26th Jul 2010, 1:12am

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MarkD

Force: 900 | Joined: 12th Nov 2009 | Posts: 7

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I tried a levels boost on the green channel with a slight improvement but it didn't solve the problem. Have you attempted your suggestion? I ended up with a complex selection of the girl / dress and a background color change ( gold hue) which seemed to blend and mask the drop out areas somewhat. Not perfect but salvageable results.
Posted: Mon, 26th Jul 2010, 9:24am

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Simon K Jones

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Thanks for uploading the images.

Comparing the red dress with the yellow and white dresses, there are some major differences. Most notably, the red dress is much more transparent, so that it is barely red in places. The mix of semi-transparent red and green makes for a problematic key.

The yellow dress, on the other hand, retains translucency but still has a definite solid shape and colouring.

Semi-transparent objects are always a challenge on greenscreen and should generally be avoided or minimised - certainly in the case of the red dress, if the girl hadn't been holding it out and thinning the material it could have worked more successfully.
Posted: Mon, 26th Jul 2010, 12:00pm

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njush

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

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Rating: +1

As Tarn said ... it's definitely an acid test situation for keying and does require extra work.
I hadn't tried my solution when I posted (wasn't near my own photokey computer) but messed with it this morning.

The process I posted before didn't fix it by itself, but it was an important first step.

Once keyed as above, I exported the PNG and did the comp in PS.
I'll try to piece together the procedure I used from there in a post later today (gotta run to catch a train).

Focusing just on the dress (I'm not happy with other areas like the hair of course), this is what I ended up with in about 3 minutes.
Posted: Mon, 26th Jul 2010, 2:36pm

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njush

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Rating: +1

OK ... so here's the 10 step procedure (it's not pretty)....

1) Adjusted green channel levels as noted in my earlier post and keyed the photo as best as possible in PK (with canvas size set to "As Foreground"). This generally worked well for the dancer's body and legs, but the dress in particular was left with a lot of solid-ish yellow blotches. We'll take care of those in photoshop, so exported the result to a PNG with no background.

2) Back in photoshop, looking at the green-adjusted original photo, go to the channels tab and review the RGB channel images to find the one that shows the best contrast in the semi-transparent material. This was the green channel.

3) Made a copy of the green channel to a new channel (just used the mouse to drag the green channel to the "new channel" button at the bottom of the channels panel) and invert the new channel so the dancer is bright and the background is black (or close to it)

4) Used the burn tool and a soft black brush on the new copy of the green channel to blacken out the areas around the the dancer. Left with essentially black solid all around, white solid for most of the dancer, and gray for the dress material. Drag this layer to the "Load Channel As Selection" button at the bottom of the channels panel to make a selection from this channel. Finally, click the RGB channel to restore our view of the image to full color.

5) Back to the Layers Panel ... click the New Layer button to add a new layer, blank layer over the original (green adjusted) image. Click the "mask" button at the bottom of the layers panel to create a mask for this layer. Since the selection should have still be based on the burned copy of the green channel, this layer mask should look like the channel work we did in step 4. Label this layer "Dress Layer" ... we'll come back to it in a bit

6) Added the backdrop image as a new layer BETWEEN the original image and the "Dress Layer". It's important that this backdrop is UNDER the dress layer, but above the original. At this point we should just see the backdrop layer.

7) Open the PNG from PK and drag that in over the "Dress Layer". Let's label this "Dancer Layer".

8 ) Add a mask to this layer, and use a soft black brush to mask away all the ugly bits of dress. Try to keep as much of this image as possible, including the hands, dense areas of dress and legs ... but get rid of all the off-color areas and semi-transparent areas of the dress.

9) Magic time .... Use the eye dropper tool to sample some red from the dancer's costume (head band works) into the foreground color. Now, select the "Dress Layer" and fill the layer with the red foreground color. You should now have something close to the image I posted above.

10) Use a brush and/or burn/dodge tools to clean up the masks in the Dress Layer and Dancer Layer to taste.

Hope this helps.
Have fun.

PS: Careful with the feet when posing dancers. Her frame-left foot should be turned out a bit more (90-degrees to camera) and the frame right side is showing a bit of sickle foot ... should be rotated to hide the heel behind the ankle from camera's POV.
Posted: Mon, 26th Jul 2010, 7:18pm

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MarkD

Force: 900 | Joined: 12th Nov 2009 | Posts: 7

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Brilliant result! You could always perform a face merge or composite to restore the hair. Well done!
Posted: Mon, 26th Jul 2010, 8:14pm

Post 13 of 13

Dave Oleary

Force: 425 | Joined: 2nd Feb 2010 | Posts: 5

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Thank you for all the advise - and detailed steps to pull this off. We will work on this today, and post our results.

dave