Something useful for a change

Started Mar 12, 2013 | Discussions thread
OP pris Senior Member • Posts: 2,191
Moire nuke recipe

Moire is rarely a problem but in some specific circumstances it can surface in the patterned parts of an image (vent covers, fabric etc). Here are steps to eliminate it in Photoshop. They take no more than 1 min but if you never dealt with LAB, first time may feel a bit overwhelming. Don't get desperate, it's really very easy and fast once you memorize the procedure. For those who are familiar with this colorspace, the procedure below is routine. Whole thing is based on the fact that in LAB the detail and the color are on different channels - sound strange but a lot of things about LAB do.

1. Create second layer (Duplicate Layer in Layers palette). If you don't have this palette on the screen, click Windows - Layers.

2. Click Image - Mode - LAB color. When the dialog pops up asking if you want to flatten the image, click Do Not Flatten.

3. In Layers palette, click tab Channels. You will see 4 channels, all of them highlighted: Lab, Lightness, A and B.

4. Click channel A. Only this channel will now be highlighted, and the image goes grey. Zoom in so you can see the moire-infected area and the pattern created by moire.

5. Click Filter - Blur - Surface blur. Move Radius slider to the right until moire-infected area loses the pattern and becomes flat-out grey. Click OK

6. Click channel B in the channel list. Now this one is selected (highlighted), and you will see the moire pattern in grey again. Repeat the procedure from p.5 with Surface blur for this channel. 
7. Click channel Lab to see the normal image again and click tab Layers.

8. Add mask to a layer, invert it to black and go over formerly moire-infected area with white brush. This step assures that no other area of the image is affected by our operation.

9. Click Image - Mode - RGB to return to RGB space

Done! Moire be gone.

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