Applied Color Theory Archive

Color Correction

Achieving Neutrality With Mixed Lighting (2004)
How to deal with counter-casts caused by different lighting within the same picture.

Is Apply Image Obsolete? (2005)
An Adobe suggestion that the command is replaced by layers draws fire, and list member Howard Smith offers a rundown on how the command works.

Banding (2000)
Discussion on combatting banding within Photoshop images and gradients.

Black&White Command (CS3 & later; 2007)
Discussion of merits of the new B/W command in Luminosity mode.

The Blend If Sliders (2005)
List member Howard Smith explains how they work.

By the Numbers/Beginners (2002)
An innocent question about elementary numbers leads to a discussion about colorspace conversions.

By the Numbers/Digicams (2001)
Discussion of how automated color correction in digital cameras can cause problems down the line.

By the Numbers/Bad Shadow (2000)
How to cope with files that arrive in CMYK with awkward shadow numbers.

The Calculations Command (2005)
List member Howard Smith summarizes how the command works and what to use it for.

Camera Raw Settings (2007)
Assuming a single image and not a group of them, does it make sense to correct aggressively in Camera Raw, or is a conservative approach in order?

Camera Raw v. JPEG (2003)
Is it really worth it to save digicam files in the RAW format? Can anybody tell the difference between it and a normally saved JPEG? The devil’s in the details.

Camera Raw: What Do We Know About the File? (2005)
List members complain that there is no guidance for how to handle Raw files supplied by second parties.

Channel Blending (2008)
Members ask about history, and how to visualize specific channels.

Channel Mixer to Make Grayscale Images (2007)
Proposals to use Channel Mixer to make better conversions to B/W.

Channel Mixer Move for Greenery (2007)
Restatement of the method of using Channel Mixer to enhance greens without throwing the color balance off.

Channel Structure, Cyan vs. Red (2007)
A PP5E reader understands that cyan and red are similar channels, but can't figure out why they appear so different in print. Dan explains.

CMYK Shadow Value (2002)
Several questions about the proper balancing of CMY to black, and how dark to go.

CMYK Techniques, RGB Devices (2003)
How to take advantage of CMYK-only correction techniques even when the output device requires RGB.

The Color Balance Command and How to Improve It (2007)
Discussion of an ancient command and how it could be updated today.

Color Bars in Art (2004)
If the original photograph contains color bars included for our guidance, how do they influence the correction process?

Color Removal (2006)
Discussion of the basics of removing a cast from a specific object.

Conversion to Grayscale and Odd Printing Specifications (2006)
A novice gets dubious advice from the printer about how dark to make the highlight.

Correcting for a Desktop Printer (2005)
Members spar over whether it is permissible to convert to CMYK during correction, assuming that the final output file must be RGB.

Curves Dialog in Photoshop CS3 (2007)
Members discuss changes to the interface.

Curves, General Information on (2013) 
Members offer suggestions on where to find basic instruction.

Cyan Lacks Detail (2007)
What to do when a CMYK image of a face is missing information in the all-important cyan channel.

Details in Daffodils (2006)
When the subject is yellow, what should the highlight be?

Digital Enlargements (2001)
Comments on how to cope with digital images that apparently don't have enough resolution for their intended use, including evaluations of Altamira's Genuine Fractals product.

Do Curves Degrade Files? (2002)
Questions about how adjustment layers vary from simple curves, and the philosophical question of whether applying curves actually damage the image.

Eliminating Lighting-Induced Yellow Casts (2004)
Dan Margulis's step-by-step channel-blending recipe.

Extreme Enlargements on Scan (2002)
Group members comment on grain control measures.

Fireworks (2005)
Dan lists some of the considerations in correcting such images, with their small areas of impossibly intense color.

Flare and How to Correct It (2005)
Dan and others discuss channel-blending methods to compensate for unwanted light sources in an image.

Fur, How to Handle (2007)
Sharpening and other considerations for dealing with animal images.

Ghosting CMYK Images (2007)
How to grossly lighten a CMYK image for artistic effect while still remaining somewhat true to the original.

Green, the Color of (2004)
A customer-supplied CMYK file containing an obviously inaccurate embedded profile leads to the introduction of a formula for determining whether greenery falls within an acceptable color range.

Greens, Natural (2005)
Target numbers for natural greens in CMYK and LAB.

Greens, Natural (2008)
More suggestions for target numbers.

Green, Three Shades of (2006, 2007)
Three interlocking threads discuss how much artistic license is acceptable in depicting natural greens. First, the use of Channel Mixer to establish brighter greens; second, at what point do the greens become fluorescent, and finally, Dan offers a better way to enhance greens in Channel Mixer, a technique not available in PP5E.

Harsh Sunlight, Overlay Blending (2004)
A preview of Dan's columns on using inverted blurred channels to boost highlights in a more flexible manner than the Shadow/Highlight command does.

High Pass Sharpening and Alternatives (2004)
Discussion of sharpening methods involving high Radius settings.

Highlights: How to Choose? (2006)
Under what circumstances should we permit them to blow out?

Highlights, Speculars, and Shadows (2005)
Some of the considerations in choosing the proper points, and deciding whether they should retain detail.

Hiraloam Sharpening: New Recommendations (2007)
Dan changes some of the recommendations on sharpening from PP5E, particularly with regard to sharpening the A and B channels of LAB.

The "Inverse Color" and How to Find It (2010) 
Dan explains why the concept doesn't work well in real colorspaces.

JPEG Artifacting (2003)
List members discuss how to remove the relics of overcompression.

Kelby Training: Dan's Videos Released (2007)
Viewers comment on the introduction of the picture-postcard workflow.

LAB: Blurring the AB Channels (1999)
How to use the A and B channels of LAB to cut down on the noise artifacts that have become more common than ever with the advent of digital cameras.

LAB: Can It Be Made More Intuitive? (2004)
The difficulty of dealing with a colorspace with opponent-color channels.

LAB: A Channel Darkening Trick (2009)
Dan points out that Darker Color mode works in LAB in some instances where Darken mode does not..

LAB: The Color Boost Action (2009)
Dan introduces an Action that deliberately makes all pictures too colorful, with the idea of backing off gracefully.

LAB: Damage During RGB/LAB Conversion? (2001)
Discussion of what happens to files when converted RGB>LAB>RGB.

LAB: Desaturation and the L Channel (2004)
Are the two techniques equivalent?

LAB: The Jacob's Ladder Technique (2008)
List member Jacob Rus introduces a novel method of correcting in LAB, using gray adjustment layers in Linear Light mode, masked by individual channels.

LAB/RGB and RGB/RGB Conversions: How Much Damage? (2006)
A lengthy and bitter discussion as to whether there is any damage at all, and how one could test for it.

LAB: Lighten and Darken Modes (2007)
They aren't available in all LAB operations. Here are the workarounds.

LAB: Opponent-Color Confusion (2006)
A list member has trouble grasping how a channel can be blue and yellow at the same time. Several responses try to make it clear, each in different words.

LAB: Role of the A channel (2001)
A question about the relative importance of the channels in LAB leads to a discussion of whether machines can generate adequate profiles.

LAB: A Schematic (2005)
A 2mb .PSD graphic of how the L, A, and B channels interact, prepared by list member Les De Moss for Photoshop LAB Color.

LAB Sharpening and Other LAB Perils (2003)
Why LAB sharpening often gives consistently better sharpening results than doing the same in RGB followed by a reversion to Luminosity. Also, a serious LAB trap for those heading for CMYK.

Linear Gamma (Gamma 1.0) (2002)
The merits and demerits of various actions when the RGB working space gamma setting is set much lower than is customary.

Linear (1.0) Gamma, Blurs, and Blends (2006)
A discussion of how Photoshop blends colors in RGB leads into a significant recommendation by Dan as to how to reduce noise in shadows by converting into a low-gamma RGB.

Luminosity and Accepted Wisdom (2008)
Should Luminosity-mode maneuvers be done on a single averaged channel, or on all three RGB channels simultaneously?

Masking Hair (2006)
Members trade suggestions on how best to make the necessary selections.

Mixing Highlight and Shadow Exposures (2003)
Is it viable to take two shots of a given scene, one exposed for highlight detail and one exposed for shadows, and then blend the two into a single image?

Moiré from LED Billboards (2007)
The photographer's assignment is to shoot billboards whose content changes every 30 seconds or so. That's plenty of time to shoot the fixed image, but the LED array that forms the billboard causes an unsightly moire in the digital capture.

Moiré in a Subject (2002)
Tips on how to handle moire caused when the subject of the photograph contains a pattern.

Multichannel Mode and Its Uses (2003)
Stephen Marsh and others discuss their recommendations.

Negatives: Reversing a C41 Color Negative (2006)
A user with several thousand of them to bring into Photoshop asks for advice.

Negatives: Scanning Color Negs (2006)
Should a scanner profile be embedded in the result?

Neutral Gray: Where Is It? (2004)
How does the beginning color corrector locate the point, if any, to be used to set neutrality?

Newsprint Printing, Correcting for (2005)
Discussion of basic considerations, with tips on handling out of gamut colors.

Overexposing: Best Way to Capture? (2003)
Discussion of a recommendation that photographs be exposed with reference to a histogram for ease in future correction.

Overlay Shadow/Highlight Enhancement (2007)
The ins and outs of this powerful method of bringing out detail.

Pepper Dots (2006)
List members share their recipes for getting rid of them.

PPW Curves, General Information on (2013) 
Members offer suggestions on where to find basic instruction.

PPW: The Luminosity Step (2013) 
A frustrated reader gets advice.

Prescreened Black and White Originals (2007)
How to scan to reduce moire.

Prescreened Color Originals (2008)
The original photo for a book cover has been lost, and only a previously printed copy is available. How to maximize quality?

A Problem with Pumpkins (2007)
The difficulty of incorporating detail into strongly colored objects, and some general solutions.

Random Spots on Older Image (2004)
How to make a correction mask based on the Dust & Scratches filter to keep noise to a minimum.

RGB and the Black Channel (2007)
How an artificial black channel can be used to correct an RGB file.

Resolution for the Future (2003)
The client, a famous photographer, wants film scanned for an unknown output condition many years from now. At what resolution should the scanning be done?

Resolution for 175-line Printing (2009)
List members find flexibility in the traditional rules.

Resolution: Upsizing (2007)
Members share their recipes for increasing file resolution

Rich Black, Fading Into (2003)
A picture sits on top of a rich black background, but the sides are supposed to vignette into it. What’s the best procedure?

Scanner Software v. Photoshop (2004)
Does drum scanner software have more capabilities than today's Photoshop?

Selecting Grays (2006)
How to produce a mask for near-neutral areas.

Shadows: Two Threads on the Basics (2006 and 2007)
How do we force neutrality in them, and what are the best RGB values if CMYK output is intended?

Sharpening Workflow (2001)
When to sharpen, and the meaning of sharpening faded to luminosity.

Sharpening: Before or After Resizing? (2007)
If a file must be resized, when is the appropriate time to sharpen?

Sharpening via Curves (2007)
List member Howard Smith suggests a method of sharpening via the weak RGB channel.

Sharpening: A New Mask Proposal (2007)
Dan suggests sharpening through a mask based on an artificial black channel.

Sharpening Objectives (2008-2009)
One of the lengthier and more informative technical discussions you'll ever read on what makes for a good sharpening filter.

Sharpening Objectives: Is the Group Losing Its Rudder? (2008-2009)
How technical is too technical? The group decides whether the foregoing thread was worth reading.

16-bit vs. 8-bit, 1999
Discussion on whether there's a significant difference in image quality if corrections are done using high bit image data.

16-bit vs. 8-bit, 2002
Dan Margulis reports on his experiences with high-bit files and sets off the usual debate.

16-bit: All Hype? (2002)
Further discussion of the merits of doubling file size to edit in 16-bit, with a report from list member Jim Rich on his findings.

16-Bit and Camera Acquire Modules (2005)
Dan Margulis reports on another test and warns that one vendor's acquire module appears to generate poor 8-bit files. He recommends that where possible files should be converted from 16-bit to 8-bit in Photoshop itself.

16-Bit: Histograms and Their Meaning (2001)
How histograms are often misunderstood, with the inevitable digression into 16-bit correction.

16-Bit and LAB (2004)
Another speaker makes the claim of superiority, and another attempt to provide a real-world example gets shot down.

16-Bit Summation (2005)
Another effort to create an image demonstrating 16-bit superiority results in another long thread with considerable namecalling, and possibly a resolution.

16-Bit Summation (Dan's history only, 2005)
In the middle of the above thread, Dan posted a lengthy history of the controversy with many quotes from both sides. It's also in the above thread, but for the convenience of those not wishing to plow through such a long discussion, it's linked separately here.

16-Bit: A Clear Case of Superiority? (2006)
List member Ric Cohn presents an example of using the B channel for a mask and suggests that using extra bits would be better.

Skies (2005)
Dan lists some of the considerations in strengthening or changing the color of skies.

Skies, Darkening of (2008)
Various strategies for strengthening lifeless skies with masks.

Skies: Noise from Channel Blending (2006)
The red channel can be a good source for strengthening the look of skies, but blending it into the rest of the image sometimes causes excessive noise. Here's how to remove it.

Skies: Why Can't They Be a Rich Blue? (2006)
A review of the CMYK weakness in saturated blues

Skies, Overexposed (2003)
Suggestions for how to add definition when the sky is blown out.

Skin Color and Smoothing (2001)
A question about proper numbers for various ethnic groups leads to various recipes for smoothing out skin.

Skintones for Babies (2003)
Appropriate balancing between magenta and yellow in young children.

Sunrise, Sunset, Reflections (2013) 
Basic principles of dealing with these phenomena are discussed.

Superadvanced Techniques (2009)
Dan reports on what transpired at the first and only set of superadvanced courses, with attendance restricted to the most serious retouchers.

Targeted Curves vs. Selections (2003)
Is it better to select areas of the image for improvement, or to apply targeted curves that may damage areas of lesser importance? The group weighs in, with quite a lot of commentary on how Ansel Adams would have done it.

Weddings, an Action for (2007)
What common maneuvers should be incorporated into an action to process wedding photographs quickly?


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