Category: Ask Tim Grey

Today’s Question: What does it mean for a color to be out of gamut, and how does it happen?

Tim’s Quick Answer: A color that is “out of gamut” is beyond the range for the current definition of available colors. One of the most common scenarios where we refer to colors being “out of gamut” relates to a situation where the printer, ink, and paper combination you’re using to print a photo can’t reproduce some of the colors defined within the actual image file for that photo.

More Detail: Ultimately, an out of gamut color is one that can’t be reproduced in a given context. In other words, when someone says that a color is out of gamut, it is always understood that it is out of gamut for a particular purpose. The color exists within our source image, for example, but can’t be reproduced with a particular type of output (such as printing).

When you’re applying adjustments to a photo, there are no colors that are out of gamut in that context. In other words, if you apply an adjustment it can only result in color and tonal values that are actually available. There is an underlying color space in use whenever applying adjustments, and that determines which colors are actually available for the image you’re working on.

If you think about tonal values I think it might be a little easier to understand the concept at work here. In a photo you are optimizing on the computer, the darkest value you can produce is black, and the brightest value is white. If you apply an extreme darkening adjustment to the photo, a large number of pixels may become black, but none of them can become darker than black. There are limits to the range of values available for a photo, you can’t produce values outside of that range.

If you print that photo, however, the darkest black that a specific printer, ink, and paper combination can produce might not be especially dark. And if the paper isn’t pure white, then the brightest value available for the print won’t be especially bright. In other words, the black in your source photo is too dark to print, and the white in your photo is too white to be represented accurately by the paper. That is essentially what “out of gamut” refers to.

While you can apply adjustments to your photos to produce any color or tonal value that is available based on the working color space in use by that software, that doesn’t mean you’ll be able to reproduce all of those tonal and color values with every possible method for producing output based on that photo.

In theory you could keep your adjustments modest so that, for example, you don’t end up with colors that are too saturated to be printed accurately. In practice you will generally want to optimize your photos so they are perfect from your perspective. Then you can determine if there are limits to how that photo can be printed through the use of soft proofing or print testing. That, in turn, may cause you to choose a specific print configuration, such as using glossy paper rather than matte paper in order to be able to produce a print with greater saturation.

In other words, colors are only out of gamut in the context of specific output, and since we tend to share our photos in a wide variety of ways that generally means we need to consider these gamut issues when producing output. When optimizing the photo on the computer, the focus is generally to produce a truly optimal source file, leaving issues of output to a slightly later stage of your workflow.

Today’s Question: When I bring an image into Adobe Camera Raw, the RAW file’s histogram shows overall clipping on the left side. If the camera is not showing clipping, how can one prevent clipping in the RAW file?

Tim’s Quick Answer: The histogram you see in Adobe Camera Raw (or any software for processing RAW captures) is based on the adjustment settings for the RAW capture. In other words, if there was no clipping shown on the camera there shouldn’t be any clipping in the RAW capture data, and so you’ll be able to recover the detail that appears to be clipped by refining the adjustment settings.

More Detail: When working with a RAW capture it is a little to see an accurate histogram, because the actual histogram really depends on how the source data is processed. Keep in mind that a RAW capture represents the actual information gathered by the image sensor during an exposure. That information then needs to be processed in various ways.

For example, I think many photographers are aware that most digital cameras only capture a single color channel for each individual pixel on the image sensor. Software then needs to calculate the “other” values for each pixel to produce full color information.

The bottom line is that there is a degree of interpretation involved when processing a RAW capture. As such, the histogram may vary based on how the information is interpreted, and what adjustments are applied along with that interpretation.

The image you see on your camera’s LCD display for a RAW capture is essentially representing an in-camera RAW conversion. That means the histogram you see on the camera is based on the in-camera RAW conversion, while the histogram you see in Adobe Camera Raw (or other RAW-processing software) is based on the interpretation of that specific software.

To add to this confusion, changing the color space option on your digital camera will generally cause the histogram to change based on that color space. So even your camera might be capable of presenting different interpretations of a histogram for a given RAW capture.

Certainly it can be a little unnerving to see different histograms for RAW captures depending on how you’re viewing the image. But rest assured that if the camera shows there is no clipping you can feel confident that the information within the RAW capture represents no clipping of data for the photo. Thus, if you see clipping in software such as Adobe Camera Raw, it simply means you need to refine the adjustment settings to refine the interpretation of the RAW data.
So, for example, simply reducing the value for Whites and increasing the value for Blacks in Adobe Camera Raw will “recover” the information that appeared to be lost on the histogram display, based on the default interpretation of the RAW capture.

Today’s Question: If a black and white JPEG image has only 256 different tonal values, which risks banding, is there any recommendation when entering exhibitions of monochrome images when the exhibition requires JPEG images only? Is it OK if the image is prepared as a TIFF and exported as a JPEG only as a last step?

Tim’s Quick Answer: As long as your adjustments were all applied to the original 16-bit per channel version of the image, and that result demonstrates smooth gradations without extreme transitions of contrast, saving the final result as a JPEG won’t cause a serious degradation in image quality.

More Detail: The primary reason it is important to work in the 16-bit per channel mode is to minimize the loss of information in the photo when applying adjustments. The various adjustments you apply to a photo can cause a loss of overall information. For example, increasing contrast can cause a reduction in the total number of tonal values represented in the image.

If you start with 16-bit per channel data, even very strong adjustments won’t likely result in posterization (the loss of smooth gradations of tone and color in an image). If, on the other hand, you start with only 8-bit per channel data, there is a very real risk of posterization, especially if you apply strong adjustments to an image.

This issue is magnified for black and white images, since there is so much less information in a black and white image compared to a color photo. With a color image you start with a theoretical maximum of more than 281 trillion possible color values available. Converting to 8-bit per channel reduces that number to a little more than 16.7 million colors.

For a black and white image you start with a maximum of 65,536 possible shades of gray when working in the 16-bit per channel mode, but only 256 shades of gray when you have converted to the 8-bit per channel mode.

As long as your adjustments are applied while working in the 16-bit per channel mode, you will minimize the impact of saving a copy of the final result as a JPEG image, which in turn means that you’ll be creating an 8-bit per channel version of the photo. Of course, it is also important to keep in mind that if your adjustments produce extreme transitions of tonal values, there may still be some posterization evident in a copy saved in the 8-bit per channel mode, even if you worked on the original in the 16-bit per channel mode.

However, if the image looks very nice in 16-bit per channel mode and you don’t apply any adjustments to the 8-bit per channel copy you create to submit to the competition, you can expect that 8-bit version to be of very good quality as well, with little or no posterization evident.

To be sure, there is still some degree of risk of visible posterization with any monochromatic (black and white) 8-bit per channel image. In the context of a photo contest I suppose you can be reassured by the fact that all images that are submitted will face the same limitations. But posterization should be minimal if you have performed all of your adjustments in the 16-bit per channel mode before creating the 8-bit JPEG for purposes of submitting a photo to the contest.

Today’s Question: Is it possible that a video card would be going bad if all of a sudden the quality of prints changes? I have an XP-610 Epson small all-in-one printer and I am unable to get a screen matching print any longer. Usually I print small out of Lightroom CC using the Spyder 4 for Color Management and prints have been excellent, but no longer. I have tried all the different option for color management and only “Managed by Printer” comes close, but doesn’t hit it.

Tim’s Quick Answer: If your prints are suddenly no longer accurate, and nothing has changed with your overall workflow and print settings, then the most likely culprit is clogged ink nozzles. For example, if the magenta ink nozzles get clogged, your prints will suddenly take on a green color cast due to the relative lack of magenta ink in the print. Cleaning the nozzles for the printer should resolve this issue.

More Detail: If there was a problem with your display adapter (video card), that would not translate into immediate problems with the accuracy of your prints. The only reason a problematic display would affect your prints is that the inaccurate display would cause you to apply inaccurate adjustments to your photos. The prints would then reflect those inaccurate adjustments.

However, if you haven’t made changes to your images based on what you’re seeing on your monitor display, then the overall display configuration would not explain prints that suddenly don’t match what you see on your display.

In my experience, this type of mismatch is almost always caused by one of two things.

The first is clogged nozzles in the printer, as noted above. Perform a nozzle check with the utility included with your printer’s software to see if there are any clogged nozzles, and perform the cleaning process for your printer if there are any issues. As noted above, this will very often resolve the type of issue you describe.

The second cause of this type of problem is a change in the overall software settings for printing. Sometimes a new software update causes a reset in the overall settings, for example. In other cases something (such as the output profile) gets changed without the user realizing it. Whatever the cause, if prints are suddenly not accurate it makes sense to very carefully check every setting related to printing.

Soft proofing the image can also be helpful in troubleshooting these types of issues. By configuring soft proofing based on how the image will be printed, you can see a simulation on your monitor display of what the print should look like. In this case I don’t believe that soft proofing will reveal any issues, but it is always worth checking to be sure if none of the other recommendations here provide a solution.

Today’s Question: When I go from Lightroom into one of the Nik filters, and I want to jump over to another Nik Filter before saving the image back into Lightroom, is that possible? I do not see any options within each filter.

Tim’s Quick Answer: It is not possible to send a photo directly from one plug-in (such as those in the Nik Collection) to another. However, if you send the photo from Lightroom to Photoshop (or Photoshop Elements) you can then apply multiple plug-in effects to the image, producing a new layer for each plug-in you use to apply an effect in the image.

More Detail: When you send a photo from Lightroom to a plug-in, a derivative image is created and in most cases you are only able to apply adjustments from that single plug-in to the current image. If you want to use a second plug-in to achieve an effect in a photo, you would generally need to select the derivative image you created for the first plug-in and send that image to the second plug-in. However, at that point a second derivative copy of the image will be created. This can obviously complicate your workflow.

Instead, I recommend using Photoshop (or Photoshop Elements) when you want to apply the effect of more than one plug-in to a photo. You can send the photo to Photoshop (or Photoshop Elements) by using the options found on the Photo > Edit In menu in Lightroom, which provide access to the External Editing features.

Once the photo has been opened in Photoshop or Photoshop Elements (creating a derivative image in the process), you can apply as many adjustments and effects as you’d like, including the use of plug-ins.

In the case of the plug-ins in the Nik Collection, each time you apply an effect with one of the plug-ins a new image layer will be created. In other words, you will have a layer-based non-destructive workflow that enables you to apply as many plug-in effects as you’d like, all within a single derivative image.

Today’s Question: I have scanned a [color] negative into Lightroom. I have tried to use the Tone Curve to turn it into a positive without success. Is Tone Curve the best approach or is there something else I should be doing?

Tim’s Quick Answer: Within Lightroom, the Tone Curve adjustment is your best option for inverting a scanned negative to convert it to a positive image. However, because of the sophisticated adjustment that will likely be required, you may be better off re-scanning the image using the software included with your scanner to convert from a negative to a positive image.

More Detail: While it is simple to invert an image from a negative to a positive (or vice versa), a photo captured on negative film doesn’t represent a simple inversion of the original scene. Therefore, a more sophisticated adjustment will be necessary.

To begin with, there may be some overall tonal variations in the negative that need to be compensated for when inverting to a positive. The bigger problem, however, is going to be color. Color negative film generally includes an “orange mask” that is designed to help improve color accuracy in the original capture. Of course, that orange mask can also lead to problematic color in the direct scan of the film (as opposed to producing a photographic print with a chemical process).

A very basic inversion of the negative image can be created with the Tone Curve in Lightroom. First, make sure you are in the Point Curve rather than Parametric mode for the Tone Curve. In other words, you want to be sure that the Highlights, Lights, Darks, and Shadows sliders are not visible below the Tone Curve itself. If those sliders are visible, click the Point Curve button at the bottom-right below the Tone Curve to switch to Point Curve mode.

Then simply drag the black endpoint from its position at the bottom-left of the Tone Curve up to the top-left corner, and drag the white endpoint from its position at the top-right of the Tone Curve down to the bottom-right. This will create a straight-line line for the Tone Curve going from the top-left to the bottom-right, and representing a tonal inversion of the photo.

At this point some fine-tuning of the overall tonality may be necessary, but the more significant issue is going to be the color. To be sure, you could make some general progress using the Temp and Tint sliders to adjust the overall balance of colors. But in reality you are going to need to apply some careful adjustments to the overall colors in the photo.

There are two approaches you can use here, and in many cases you’ll want to use both approaches to correct the color for a scanned negative. The first is to apply a Tone Curve adjustment for each individual color channel. For each channel (red, green, and blue) you’ll need to apply a Tone Curve to shift the balance of colors within the photo, with a different shift commonly needed for the shadow areas versus the highlight areas.

You can also improve the color with the Hue, Saturation, and Luminance sliders in the HSL section of the right panel in the Develop module, shifting the Hue (overall color balance), Saturation (color intensity), and Luminance (color brightness) for each individual color.

It can take considerable work to get the color just right when working with a scanned color film negative. In most cases, the software included with your scanner will provide you with a much better starting point for a scanned negative. Even though each film stock has different issues related to overall color, most scanner software does a good job of providing a reasonably good starting point for the image in terms of the overall tone and color quality of the initial film scan. In other words, you may find that it is much less work to go back and re-scan the original negative rather than applying some sophisticated adjustments to your initial scan.

Today’s Question: How can you make a “one time only” adjustment when exporting photographs from Lightroom, so the adjustment won’t be in effect next time you edit the image?

Tim’s Quick Answer: There are a couple of ways you could approach this, but my recommendation is to create a Virtual Copy in Lightroom when you want to make a “one-time” adjustment for purposes of exporting with special settings. You can then delete the Virtual Copy when you’re finished.

More Detail: Lightroom enables you to create Virtual Copies, which provide the ability to create different versions of the same source photo, with unique adjustments for each Virtual Copy you create. In the case of wanting to create a unique version of a photo to be exported for a particular purpose, you could create a Virtual Copy that will include those specific adjustments. You could then delete the Virtual Copy if it is no longer needed, and at any time could return to the original image, since the Virtual Copy won’t have altered the original.

To create a Virtual Copy in Lightroom you can simply right-click on the photo you want to create a new version of and choose the “Create Virtual Copy” option from the popup menu that appears. This will create another copy of the photo as a Virtual Copy, without actually duplicating the source image on your hard drive. The thumbnail for the Virtual Copy will have a turned-up corner graphic to help you identify the copy compared to the source image. The filename for the Virtual Copy will also indicate “Copy”, along with the copy number, after the actual filename for the source image.

The Virtual Copy will inherit the current adjustment settings for the source image when you create the Virtual Copy. However, you can then go to the Develop module and apply any adjustments for this specific version of the image. For example, I often need to create a version of a photo that is cropped to a specific aspect ratio for certain publication uses. You can apply any adjustments you’d like, however, for the Virtual Copy.

When you use the Export feature to create a file based on the Virtual Copy, that exported image will of course reflect the adjustments you applied to the Virtual Copy. And when you’re finished working with this unique version of the original photo, if you don’t need the Virtual Copy anymore you can delete it. To do so, simply right-click on the Virtual Copy and choose “Remove Photo” from the popup menu that appears. You will be asked to confirm that you want to remove the selected Virtual Copy, at which point you can click the “Remove” button to actually remove the Virtual Copy from your Lightroom catalog. The original image will remain in place in your catalog and on your hard drive, unaffected by your work on the Virtual Copy.

Today’s Question: I am hoping to get some insight on how Depth of Field is influenced by the variables of Aperture, Subject Distance and Lens Focal Length.

I have recently come across websites that indicate that the common assumption that Depth of Field is influenced by Aperture, Subject Distance and Lens Focal Length is in fact, erroneous.  Specifically, the first 2 variables, Aperture & Subject Distance do affect Depth of Field (DOF), while Focal Length has no effect on DOF.

To further confuse matters, a number of reputable web sites provide online DOF calculators (and also downloadable Apps). Why is focal length included as a factor to be added to the calculation for DOF?

Hoping you can provide ‘clarity’ on seemingly contradictory situation.

Tim’s Quick Answer: I would argue that lens focal length does indeed impact depth of field. A longer focal length will result in less depth of field. That said, I would also argue that distance to subject and lens aperture to be the more important variables to consider.

More Detail: Those who argue otherwise generally stipulate that if you frame the subject the same way, suddenly focal length is not a factor. But in order to accomplish that change in framing you must also change the distance to the subject. In other words, you would be changing one variable (distance to subject) in order to pretend that another variable (lens focal length) was not a factor.

In other words, I could also argue that distance to subject has absolutely no bearing on depth of field, but that instead it is a change in focal length that alters depth of field. If you change your adjust your focal length you obviously must change your distance to the subject to maintain the same framing, so I could argue that it is the focal length (and not the change in distance) that caused the change. But that is obviously (I hope) not a reasonable argument.

In reality, all three factors (distance to subject, lens aperture, and lens focal length) impact the final depth of field you will achieve. And in fact there are additional factors, such as the overall image sensor layout (the size of each “pixel” on the sensor, for example) that also have an impact on depth of field.

To be sure, the calculations involved in determining depth of field for a given photographic situation can be a bit complicated. But as far as I’m concerned there is no question that distance to subject, lens aperture, and lens focal length play the primary (though not exclusive) role in determining final depth of field.

Today’s Question: You said something in a recent post on exposure for RAW captures (November 16th) that goes contrary to what I have always been lead to believe. You said that you feel it is better to (if necessary) OVER expose an image without blowing out highlights to preserve detail. I was always thought that it is better to UNDER expose (if necessary) the image to preserve detail.

Tim’s Quick Answer: For a digital capture, it is indeed best to capture an exposure that is as bright as possible without blowing out highlight detail. That differs from exposure for slide film, for example, where it was generally better to err on the side of an under-exposure in part to preserve saturation and detail in the image.

More Detail: Part of the issue here relates to how the information contained within a photo is being captured. In a very basic way, you can think of more information as being “good”, at least up to a point. In other words, you want as much information (light) to be recorded as possible, without capturing so much light that you’ve blown out all of the detail in a photo.

In the context of slide film, a slightly dark exposure provides greater density, which in turn can provide greater color saturation and possibly more detail. Thus, the general rule of thumb with slide film is to slightly under-expose the image. You don’t want to go too far, but when in doubt it is generally better to expose slide film slightly too dark rather than slightly too bright.

With digital cameras, a dark exposure is generally not going to produce the best results. By capturing as much light as possible without actually clipping highlight detail, you’re capturing as much detail as possible. An image that is captured with an exposure that is too dark contains less information, and will exhibit more noise when you need to brighten up the image to produce a better final result.

So, with digital photography the best exposure in terms of maximum detail and minimum noise is an exposure that is as bright as possible without clipping highlight detail. This may, of course, require a bit of darkening of the image in post-processing, but in my mind that is a small price to pay in order to ensure the maximum possible detail and the minimum possible noise, all other things being equal.

Today’s Question: Is there a way to prevent exposure clipping of a specific color channel? I noticed that I was getting clipping of the blue channel on the left side of its histogram (no other color channels were clipped) and the combined RGB histogram and luminosity histograms showed no clipping on the back of the camera.

Tim’s Quick Answer: Preventing the clipping of a single channel requires that the overall exposure is adjusted, which in turn can require a review of the individual histogram channels for the image you’ve captured. And, of course, in some cases a single channel can be enough to require multiple exposures to create a high dynamic range (HDR) image.

More Detail: When a single channel is clipped, it means you have lost detail for that channel. In other words, you’ve captured an exposure that is less than optimal. In many cases you can compensate for this type of issue when processing your RAW capture on the computer, but I always recommend getting an optimal exposure in the camera.

It is important to review all three color channels (red, green, and blue) rather than just the overall luminosity histogram for a capture. Even when the luminosity histogram indicates there is no clipping of highlight or shadow detail for a photo, there may still be a loss of detail on an individual channel.

To be fair, in some cases it is not critical to retain detail for all three color channels in a photo. However, it is always better to have detail you don’t need than to lose detail you later wish you had.

When it comes to the original capture, the best approach to evaluating your exposure settings is to configure your camera to display individual histogram displays for each color channel. Most cameras include this option, or the option to overlay the histogram for all three color channels into a composite display. If a single color channel indicates it is clipped on the histogram, it is probably worthwhile to adjust your exposure settings and capture another image.

It is worth noting that the color space setting on your camera has an impact on the histogram being displayed. As a general rule I recommend using the Adobe RGB color space option in your camera in order to provide a more accurate histogram display. The sRGB color space option will generally provide a more pleasing image preview on your LCD, but a histogram that isn’t quite as accurate compared to the final result you can expect.