gefillmore
28th December 2006, 02:43 AM
Color and Contrast by LAB Mode: the Rudimentary Steps
This is a partial summary of Chapter 4 in Dan Margulis' book Professional Photoshop.
(for much more advanced text, examples and discussion, please see Dan Margulis’ book, Photoshop LAB Color: The Canyon Conundrum and Other Adventures in the Most Powerful Colorspace).
The LAB mode is best used when you a have a photo with drab, dull colors. Using LAB will drive the colors apart. Also. LAB mode will treat colors and contrast separately, which will be seen to be very handy as we move into the chapter.
Photographs that have bright and different colors are not the best subject for improvement by the LAB mode. As stated, Lab mode drives colors apart and these type of images are already there.
http://gefillmore.smugmug.com/photos/119305947-M.jpg
Not for LAB mode adjustment
I have chosen a photograph of a barn I took just for the purpose of demonstrating the benefits of the LAB mode:
http://gefillmore.smugmug.com/photos/119306189-M.jpg
Jpeg copy of the raw file
First, I have attempted to improve the picture with the standard levels and curves in RGB mode (I usually try to do this intuitively).
I have positioned this image just above the LAB mode improved image for comparison purposes.
Now I am going to adjust the photo in LAB mode. Go to Image: Mode>Lab color. Then open Image: Adjustments>Curves. Your first screen is the Lightness channel. Photoshop default for LAB mode curves is to have black input, output at 0, 0. Left click on the white triangle in the black-to-white bar underneath the graph and that will switch it to white input, output at 0, 0. This will put you in synch Margulis’ writings and examples (and mine).
Please see curve image A below for lightness channel contrast adjustment.
You more or less curve this to taste. You can use the cursor on the photo to tell where on the curve that particular area of the photo will be affected when you move the curve. This is very sensitive and you have to adjust incrementally.
Now, on to the AB curves. Simply put, you move the top and bottom endpoints in by equal amounts, making sure the curve stays over the center point. The center point is a neutral area (white, black, or neutral gray). If you move the curve at this point, you are getting into adjusting for color casts. Not that this is an invalid adjustment, we’re just keeping it simple right now and making a basic adjustment on an image.
Please see curve image A below for a and b adjustments.
Below is the image after the Lightness, A and B channel curve adjustment with the RGB mode image above it for comparison:
After levels and curves adjustments in RGB mode
http://gefillmore.smugmug.com/photos/119306425-M.jpg
http://gefillmore.smugmug.com/photos/119306667-M.jpg
After LAB mode curves adjustments
http://gefillmore.smugmug.com/photos/119306740-M.jpg
Curve Image A. LAB mode curve adjustments for barn image
You can sharpen the image by going to the Channels palette, clicking on the Lightness channel, then opening up Filter: Sharpen>Unsharp mask. For Amount, use 200%. For Radius, use 1.0 pixels. And for Threshold, use 10 levels. What type of sharpening you use depends much on the image, the resolution, what your tastes are, your audience.
Then click on Lab in the channels palette to bring the image back to color.
http://gefillmore.smugmug.com/photos/119307294-L.jpg
Lab mode adjustment and sharpened
You almost always want to put the image back into RGB mode before saving, printing, or moving to the web (Image: Mode>RGB color).
Remember, LAB adjustments will increase the differences between colors, but it is only worthwhile if the differences are not too big to begin with.
This is a partial summary of Chapter 4 in Dan Margulis' book Professional Photoshop.
(for much more advanced text, examples and discussion, please see Dan Margulis’ book, Photoshop LAB Color: The Canyon Conundrum and Other Adventures in the Most Powerful Colorspace).
The LAB mode is best used when you a have a photo with drab, dull colors. Using LAB will drive the colors apart. Also. LAB mode will treat colors and contrast separately, which will be seen to be very handy as we move into the chapter.
Photographs that have bright and different colors are not the best subject for improvement by the LAB mode. As stated, Lab mode drives colors apart and these type of images are already there.
http://gefillmore.smugmug.com/photos/119305947-M.jpg
Not for LAB mode adjustment
I have chosen a photograph of a barn I took just for the purpose of demonstrating the benefits of the LAB mode:
http://gefillmore.smugmug.com/photos/119306189-M.jpg
Jpeg copy of the raw file
First, I have attempted to improve the picture with the standard levels and curves in RGB mode (I usually try to do this intuitively).
I have positioned this image just above the LAB mode improved image for comparison purposes.
Now I am going to adjust the photo in LAB mode. Go to Image: Mode>Lab color. Then open Image: Adjustments>Curves. Your first screen is the Lightness channel. Photoshop default for LAB mode curves is to have black input, output at 0, 0. Left click on the white triangle in the black-to-white bar underneath the graph and that will switch it to white input, output at 0, 0. This will put you in synch Margulis’ writings and examples (and mine).
Please see curve image A below for lightness channel contrast adjustment.
You more or less curve this to taste. You can use the cursor on the photo to tell where on the curve that particular area of the photo will be affected when you move the curve. This is very sensitive and you have to adjust incrementally.
Now, on to the AB curves. Simply put, you move the top and bottom endpoints in by equal amounts, making sure the curve stays over the center point. The center point is a neutral area (white, black, or neutral gray). If you move the curve at this point, you are getting into adjusting for color casts. Not that this is an invalid adjustment, we’re just keeping it simple right now and making a basic adjustment on an image.
Please see curve image A below for a and b adjustments.
Below is the image after the Lightness, A and B channel curve adjustment with the RGB mode image above it for comparison:
After levels and curves adjustments in RGB mode
http://gefillmore.smugmug.com/photos/119306425-M.jpg
http://gefillmore.smugmug.com/photos/119306667-M.jpg
After LAB mode curves adjustments
http://gefillmore.smugmug.com/photos/119306740-M.jpg
Curve Image A. LAB mode curve adjustments for barn image
You can sharpen the image by going to the Channels palette, clicking on the Lightness channel, then opening up Filter: Sharpen>Unsharp mask. For Amount, use 200%. For Radius, use 1.0 pixels. And for Threshold, use 10 levels. What type of sharpening you use depends much on the image, the resolution, what your tastes are, your audience.
Then click on Lab in the channels palette to bring the image back to color.
http://gefillmore.smugmug.com/photos/119307294-L.jpg
Lab mode adjustment and sharpened
You almost always want to put the image back into RGB mode before saving, printing, or moving to the web (Image: Mode>RGB color).
Remember, LAB adjustments will increase the differences between colors, but it is only worthwhile if the differences are not too big to begin with.