Tuesday, November 18, 2008

Photoshop techniques for foxing, and for stereo images

From: "Moses Gershbein" moses_gershbein@laughingelephant.com

For foxing or the gradual tanning of the paper, presenting a shaded background rather than a white background to the picture, I first try to separate red, green, blue channels. One of these channels will usually have a majority of the foxing. You can eliminate this channel and convert to black and white. Another method is to examine the pixel histogram in a software program. The off-white background will appear as a big hump at one end of the histogram. Slicing these pixels out of the picture will eliminate foxing ... be careful not to lose detail. If the picture was captured at 16 bits, the remaining pixels will be adjusted to give a full 8 bit grey scale image on down conversion. Scanning at 16 bit, you'll need to double the size of the ultimate size you're wanting, as you'll need to convert to 8 bit once you've edited the image, in order to save as tiff or jpg formats.

For the issue of color matching "stereo" images, you'll need to create a mask in Photoshop of the side of the image which you'll be editing to match the other. this is done in "quick mask" mode. Make sure to use a large soft brush to select the edge between the 2 sides. Once you've painted in the space to be adjusted, exit quick mask to reveal the marque around the selection. Then, from your layer pallet, select the layer adjustment (yin & yang looking symbol) and choose either curves, levels, or hue saturation. one or all of these can be used to alter the image for the desired result. This is a much more involved procedure and will require a skilled Photoshop user. ...


Moses Gershbein
Blue Lantern Studio