Meeting 7
Chi va piano va sano e va lontano
Topics: Color Correction, Color Replacement, and Channel basics.
Color correcting pictures well requires a basic understanding of color relationships. Complementary colors are those opposite each other on the color wheel. To view the color wheel, click here.
Optional: How good is your color perception?
FACT: 1 out of 255 women and 1 out of 12 men have some form of color vision
deficiency.
Open this XRite
web link
to take an
online interactive test based on the official FM100 Hue Test.
Toning in Camera RAW
Note that if you have camera RAW files available, you should do the majority
of the toning in the RAW software to avoid the data loss and potential quality
problems that arise from toning in Photoshop. Toning in RAW software is
reversible at a later date. Once file is "baked" into a Photoshop
file, or saved as a JPG, TIF, etc. file, then you are performing destructive and
non-reversible changes.
Another reason for toning in RAW is that you are working with a higher bit-depth file that permits greater adjustment without posterization or increased noise. You can work in higher bit depths in Photoshop, but the original must be a high bit-depth image for it to make any difference.
Finally, RAW files contain information at the extreme dark and light ends of the tonal range, and adjustments may be able to save a photo with blown-highlights, for example.
When you first view a camera raw file in Adobe Camera RAW (usually through Bridge), you are presented with a view of your picture as shot, and a host of controls along the right pane. In addition, other tools that let you dodge or burn, remove spots, crop and more are shown as little icons at the top of the dialog box. At the bottom (and usually shown in blue text) are the workflow options as currently selected.
Click the links below to jump to explanations for some different sections of the Camera RAW program...
Main window
Adjustment brush
Graduated Filter
Color Sampler
Spot Removal
Workflow options
There are other toning options in addition to the linked tasks shown above. For example you can reduce noise, or correct for chromatic aberration of lenses in the various tabs shown near the top of the right-hand side control panel.
Toning RGB files in Photoshop
Still, there are times when toning RGB (or even CMYK) in Photoshop needs to
be done. The following exercises show several approaches. Toning RGB pictures in
Photoshop is usually destructive (except for adjustment layers - explained in
Meeting 9 - that avoid lossy toning). If a user
takes too many attempts at toning an RGB picture, they may reach a point when it
becomes impossible to adequately correct it. If this point is reached, then it
is best to start from a fresh copy of the file - if it is still available.
Open 07begin.psd (Exercises 4). Also open 07final.psd file as a reference target for our adjustments.
Use Image>Adjustments>Curves command on 07begin.psd (Exercises 4)...
Image>Adjustments>Curves
To make adjustments in Curves, the best way to begin is to click near the center of the curve graphic to add a control point, then drag it at right angles to the curve itself. This "curves" the curve, and adjustments are immediately viewable. Most color correction is iterative - meaning that it's mostly trial and error adjusting the various channels to obtain pleasing color. An experienced operator will be able to identify the off-colors present in the picture, then quickly choose and adjust the appropriate curve to correct the picture.
When the dialog box first opens, the composite (RGB) curve is shown. Adjusting it affects only how light or dark the image is because all curves are adjusted equally. However, I generally adjust the RGB channel for proper lightness/darkness last - after I've corrected the other channels for color. Different channels (Red, Green. Blue) can be selected in the Channel drop down list to adjust the corresponding curve. If Red is chosen in the drop down list, only the red channel is affected by curve adjustments. Green and Blue channels are also adjusted individually once they are chosen. Remember the color wheel as you identify colors in your picture to correct so you can target the proper channel for adjustment.
*(Optional) Use the Black point eyedropper to set the black point.
*(Optional & very dangerous) Use the White point eyedropper to set the white point.
*(Optional) Use the gray eyedropper on a neutral toned object to set the overall color balance for the photo.
Note that there is a "Save Preset..." selection in the Curves dialog box to save a set of corrections to be used on future pictures. It's nested behind the small dialog icon (horizontal lines) at the top. This is useful if a device or circumstance imparts a repeatable color cast to images -- the same correction can be applied to all photos once one is corrected. Use the "Load Preset..." button to load a previously saved set of corrections.
TIP: Extreme toning changes can produce unwanted shifts in color saturation and contrast. For example, greatly lightening an underexposed picture can make faces very red, and affect shadow colors adversely. To better maintain color and contrast, try changing the picture's Mode to LAB color temporarily. Run curves and make changes to the Lightness channel (the L in Lab), while leaving a and b channels untouched. Convert back to RGB when you are finished.
Sometimes Saturation is the problem...
Open the file redhead.jpg in Exercises 4.
Try to adjust color using curves... it will be difficult. The problem with this picture is mostly excessive color saturation. Over-saturated color is often perceived to be "brilliant" and manufacturers of film offer some film varieties that have more saturation than normal. These films also tend to be high in contrast, and some scanners tend to amplify the already high-contrast tones.
For the redhead.jpg picture, use Image>Adjustments>Hue/Saturation to desaturate the orange color that is the problem in this picture using the following steps:
After opening the dialog box, change the Edit field from Master to Reds.
Click on the eyedropper in the dialog box and then click on the saturated orange cheek of the girl.
Move the Saturation slider to the left to reduce saturation.
Adjust the color selection slider at the bottom to pick up some yellows that are too saturated too.
The picture should now look more life-like.
Karl Kuntz Method 1:
The Columbus Dispatch uses a process devised by Karl Kuntz to correct color in some
off-color photographs. The steps are listed below:
In the Image>Adjustments>Levels dialog box, Click on the Channel drop down box, and choose the Red channel.
Slide the black point triangle for the Red channel to the beginning of the picture histogram data on the left side. Side the white point at the beginning of histogram data on the right side.
Now choose the Green channel and the Blue channel and do the same thing to their black points. Adjusting the black points of each channel individually should get color close.
Go to the RGB Channel and adjust the overall black point and gray point.
Click OK to accept the Levels changes.
Now open the Curves dialog box: Image>Adjustments>Curves.
Now adjust the Red, Green, and Blue curves individually to fine-tune the color correction needed for a good photo. Click OK when done.
Try these steps on the file called tree-lined big.jpg (Exercises 4), then fine-tune using curves.
I have found that a picture that has been adjusted first using Curves can be fine-tuned by the above method (a bit of a reverse of Karl's method). For example, a color cast in the darker tones of an otherwise good correction may be eliminated by choosing Levels and then moving just the black point triangles in each channel to the beginning of the data in the histogram.
Be especially careful of moving the white point to histogram data to force some parts of a picture to white. Some pictures shouldn't have a white, and forcing some data to white will blow-out highlights. For example, using this technique on the Bale Hop toning assignment will make the hay bales excessively high in contrast with white highlights where there shouldn't be any.
I have also found that this method works better with some pictures than with others. The Food at Hadrian's toning exercise given at the end of this lecture responds nicely to this technique. The careful toner will still need to have a good eye for color to judge whether this method solves the color problems.
Karl Kuntz Method #2 Using the Curves White-Point Eyedropper:
Sometimes you wish to neutralize a very light tone (white shirt, snow, etc.) that may have
a color cast. This method works very well with some pictures, but won't correct 100% of
them. However, it may provide a very close solution that can be further tweaked with many
images.
Begin by setting your Eyedropper tool to a 5x5 sample area on the Options bar.
With an off-color image open (use costumed_skater.jpg in Exercises 4), open the Curves dialog box (Command-M).
Double click the white-point eyedropper in Curves to open the Color Picker window. You should see the dialog box as shown below.
Next click in the picture itself on an area that you wish to make neutral white (white shirt, ice, snow, white wall, etc.) In our example, find a highlight on the ice.
The color of the spot you sampled in the picture is displayed in the "Select target highlight color" dialogue box and that color numbers are shown for it. The Lab color settings for Luminance, a, and b are displayed together with other color methods. L is the luminance channel and varies from 0 (black) to 100 (pure white). Don't change luminance, but do change the a and b numbers to zero. This makes the color neutral - no color cast.
Click Ok to return to the Curves dialog box.
Click again in the SAME SPOT using the newly reconfigured white-point eyedropper in the Curves dialog box. The color you clicked will now become neutral gray, and other colors will shift with it. With Curves still open, you may further tweak the tones as desired.
Click OK in the Curves dialog box, and choose NO to the prompt to save the new target color as the default for the white-point eyedropper.
This method works with pictures that contain neutral tones - white snow, white shirts, Kodak gray cards, etc. If there is nothing in your picture that contains a neutral tone, don't waste your time with this method.
Big Tip
Adobe Bridge CS3 introduced the ability to use Camera RAW to tone JPGs and TIF files, and it continues in CS5. To enable this in CS5, start Adobe Bridge, go to Camera RAW Preferences (under the Adobe Bridge CS5 menu item at the top), go to the JPEG and TIFF Handling section, and choose "Automatically open all supported JPEGs". Do the same for the TIFF format.
Toning problem pictures may be easier with the two color sliders at the top of the Camera Raw converter compared to using Curves in Photoshop. However, some of the advantages that you have when toning Camera RAW will not be available when toning JPGs or TIFs. For example, blown highlights will remain blown out, and you can't fix them like you can with a RAW file.
If you don't want Camera RAW to open your JPGs or TIFs, choose "Disable JPEG support" and "Disable TIFF support".
To experiment, set the Camera Raw preferences in Bridge to "Automatically open all supported JPEGS" and open in Camera Raw the untoned JPG file _DSC9389.JPG from my digital image folder Exercises 4 > For Bridge > more studio shots>_DSC9389.JPG. It is a photo of young ice skaters made with a studio strobe and a Nikon D2X, but for some reason, all the photos are a little Pepto-Bismol pink. It is much easier to tone this JPG in Adobe Camera Raw than it is in RGB in Photoshop.
Once you are done with this experiment in our lab, please set the preferences back to the default of Disable JPEG and TIFF support in the respective boxes. That way the preferences won't confuse a subsequent lab user. On your own personal computer, you can leave it as you want.
Another Tip:
Use Image>Adjustments>Replace Color to select and de-saturate residual color casts
in a picture. This is most useful when there is a stubborn cast remaining after other
color adjustments are used to get close. One use is removing residual green in some
pictures made under fluorescent lighting.
Replacing Colors in an Image with Other Colors
There are a variety of ways to change colors in an image. They include:
1) Use a brush with Color mode selected in the Options bar. This is useful for local touch-up of color or small replacement jobs. The steps are:
Open a file (use 07final.psd in Exercises 4).
Select the brush tool.
Check the Options bar and select Color in the Mode drop down list. (By default it will indicate "Normal")
Select an appropriated brush size.
Choose the color you wish to use -- it must be selected as the foreground color.
Paint over the area that you want to change.
(NOTE: If you have adjustment layers above the original image, you must select the layer that contains the original image to replace color. Adjustment layers will be discussed in Meeting 9)
If you have an advanced need for color replacement, there is a Color Replacement Tool in the toolbox that already has the Mode on the options bar set to Color as above. It has more finesse, especially in the ability to "stay within the lines" through sampling . Its use is otherwise identical to the previous steps.
2a) Use Image>Adjustments>Replace color. This method is useful if the image contains a multitude of scattered detail that is comprised of a similar color. Using the Paintbrush tool on this type of image would be possible but tedious.
Open (or Revert to) 07final.psd
Choose the Eyedropper tool and select a color you wish to change throughout the image (in 07final, click on one of the red peppers).
Image> Adjustments> Replace Color
Adjust the Fuzziness slider to select more or less colors that you want to change. Notice how the chef's lips (also red) are also selected if fuzziness is set to a high number. That can be prevented if preliminary steps are taken (detailed later).
Change the Hue slider to affect the color of the image. Saturation and Lightness sliders can also be adjusted to achieve a desired effect.
Click OK
Done
2b) If you wish to change the reds in the peppers but not anywhere else in the image (for example if you wanted to exclude the lips from a hue change), first lasso around the region of the image you wish to affect before performing the steps given above. Here are the steps needed to change instances of a color in just a small region of the picture:
File>Revert the 07final image to its original form.
Choose the Lasso tool and roughly select the bowl of peppers.
Choose the Eyedropper tool and select a color you wish to change throughout the selected part of the image (in 07final, click on one of the red peppers).
Image>Adjustments>Replace Color
Adjust the Fuzziness slider to select more or less of the similar colors you want to change. Notice how the Fuzziness preview is restricted to approximately the region defined by the lassoed selection. It does not display the full image as before.
Change the Hue slider to affect the color of the image. Saturation and Lightness sliders can also be adjusted to achieve a desired effect.
Because the lassoed area does not include the lips, they remain unaffected by the changes made in the Replace Color dialog box.
Click OK
Done
3) Use Hue/Saturation to colorize overall or to affect only certain colors.
File, Open 07final.psd (or you can revert if already open).
Choose Image> Adjustments> Hue/Saturation
To colorize overall, click the Colorize check box. Saturation usually should range from 20-40 for pleasing tones. Adjust the Hue slider to choose a desired color.
Click OK
Done
This resembles a Duotone mode picture, but it is still an RGB mode picture and NOT a duotone. This method is the way to colorize pictures for the web (an RGB world). Duotones are for print ONLY and will be discussed in a later meeting.
If you don't wish to completely colorize a photo, you can still shift the overall image color by not clicking on the Colorize button in the dialog box. For example, Saturation can be greatly reduced to give a tinted B/W photograph appearance to a color photo.
Tip: The Nikon scanners and Fuji color negative film often produce super-saturated reds. They are unrealistic. To make the red more natural, use Hue/Saturation, click on the Reds button, and slide Saturation to something less than zero.
Channels:
Channels carry color information in color pictures, and additional channels can
be added to be used as a place to store selections that might get used more than
once. Channels can be viewed by clicking on the Channels tab
in the Layers Palette or by going to Window> Show Channels.
Open 07after.psd and show how the red, green, and blue channels are displayed in the
channels tab.
An exercise in manipulating the color Channels:
Open JOE.TIF and convert to RGB.
Click on the Channels tab in the Layers Dialog box.
Choose the red channel (click its name) and Filter>Pixelate>Mezzotint for special effect. Click back on on the RGB channel to view the effects on the picture.
Choose the green channel and Image>Adjustments>Threshold. Slide the adjustment to give a fairly good representation of the image.
Return to the RGB channel to view these effects.
Open JOEFANCY.TIF to show what can be done with a plug-in filter operating on the red
channel. This is a sample of Andromeda's Screens plug-in filters.
Saving selections as channels, and turning a channel back into a
selection:
This is a handy way to save a hard-won selection and to be able to use it
repeatedly - even after a file is closed, then reopened.
Open Maple.jpg.
Use the Magic Wand tool (W) to select the background.
Select>Inverse
Click the Save Selection as Channel button at the bottom of the Channels Palette. It looks like a shaded square with a round dotted circle inside.
A new Channel appears named "Alpha 1" by default.
Now choose Select>Deselect (Command-d) to drop the selection. The marching ants disappear.
Bring back the selection area by going to Channels, and dragging the new channel to the Load Channel as Selection icon at the bottom of the Channels Palette. It looks like a dotted circle without a bounding box.
The marching ants reappear, confirming that the previous selection has been re-applied.
This technique is invaluable in complex images after you spend time carefully selecting a part of your picture. You can reapply a selection any time after it has been created and saved as a channel.
The History Palette
The History Palette combined with the History brush can aid a Photoshop worker when
adjusting parts of a picture. For a 5 minute on-line tutorial, follow this link for a Quicktime Movie. (NOTE: BIG
file - about 40MB. It plays best if you first download it, then play it)
Stump the Chump Invitational Toning Challenge
In the class meetings that follow, I invite the submission of pictures you'd
like to see toned. I will pick one, tone it, and show the steps in future
meetings. I hope to do this once per week.
If you have pictures you want to submit to me for toning, drop them into the Stump the Chump folder I will set up on the server. I will pick one picture from the submissions, tone it, and present the toned picture in class with steps for toning it.
If you wish to also tone the picture yourself to see if you can do better (Stump the Chump!), help yourself! We can project the comparison onscreen in class, but please document your toning steps to share with the rest of the class.
| Tech Exercises 3: | Turn-in_03 folder - Due April 27 | ||||||||||||||||
| Color correct the xmas_tungsten.tif file. (The following files can
be found in Exercises 4) Color correct the allen green1.psd image by whatever means you desire. Color correct the food at hadrians_sm.jpg file Selectively color-correct different regions of the bale-hop.psd image (Exercises 4) to make a pleasing picture overall. Be sure that the tilt of your LCD screen is correct before making judgments about tone. Remember that notebook computer screens are often poorer choices for toning than fixed monitors because of the tradeoffs involved in reducing size and power requirements. Some models can't be calibrated or trusted for critical toning at all. Please save files in the JPG file format to save space (non-JPG files will be discarded without a grade!). Place all files in Turn -In #3. Be sure to add your last name as part of the file name! Do NOT submit your files together in a folder that you make! Please submit files individually. Thumbnails of the corrected files appear here to aid your own work.
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