Blue Channel Limitations

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Today’s Question: In “Evaluating Photos” you talk about the blue channel being the weakest channel. Is there anything I can do in camera to strengthen that?

Tim’s Quick Answer: Not really. Creating a good exposure, or even better an exposure that is as bright as possible without losing highlight details, will help ensure a relatively “strong” blue channel. But the blue channel in an RGB image will still generally be the “weakest” of the three channels in terms of overall quality.

More Detail: In general you will find that wavelengths of light that fall into the “green” range will generally be strongest in a photographic scene, with the “red” range typically being second. The “blue” range is generally the weakest. This is partly because more green and red light tends to be reflected in typical photographic scenes, and partly because image sensors (and the human visual system) are less responsive to blue light.

As a result, you’ll often find that the blue channel in an RGB (red, green, blue) image tends to be the weakest channel, with more noise and less overall detail than the other two channels. When the photograph was captured under relatively bright lighting conditions, the relative lack of quality in the blue channel won’t represent a serious problem. But when noise (and lack of detail) in an image is of particular concern, the blue channel is likely to be a significant contributor to the problem.

While there isn’t much you can do other than ensuring an optimal exposure, it is worth being aware of the potential for challenges with the blue channel, and to review all of the channels as noted in the “Evaluating Photos” course in the GreyLearning library.

If you’re not already a GreyLearning subscriber, you can sign up for the “Everything” bundle to gain access to the “Evaluating Photos” course as well as all of the other courses in the library. You can get more details here:

http://greylearning.com

TIFF Transparency

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Today’s Question: How do you get transparency in a TIFF file?

Tim’s Quick Answer: Transparency in a TIFF image is achieved by either erasing pixels or (preferably) by using a layer mask to hide pixels. However, most applications will not automatically reflect that transparency.

More Detail: This question was something of a follow-up to a question (or two) that previously addressed the PNG (Portable Network Graphics) file format, which supports transparency. What transparency means in the context of a PNG image is that most applications will actually support the transparency, so that whatever is “behind” the image will show through in transparent areas. For example, PNG images with transparency are often used on a website for situations where you want to be able to change the background color of the website without having to modify the PNG image.

For TIFF images the situation is slightly different, since TIFF images are typically used for scenarios that are different from the typical scenarios for PNG images. For example, while PNG images are often used for websites, TIFF images are typically used for printing and other situations that tend to call for larger overall image sizes (and in some cases more advanced features).

For some applications (such as page layout applications) a saved selection (or other layer mask or alpha channel) in a TIFF image can automatically be used as a mask for the image. In other words, even if the master image actually contains a full rectangular arrangement of pixels, an alpha channel can be used so that only the area defined by a saved selection or layer mask is shown when the image is placed in a document.

So, if you want to preserve transparency when saving a TIFF image, you really just need to preserve any layer masks, saved selections, and alpha channels that were used to create that transparency in Photoshop. Just keep in mind that only certain applications will actually present the image with that transparency, since the image is at that point a layered image that for the most part can be thought of as a Photoshop-only image file.

Consolidating Subfolders

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Today’s Question: I find that I have created a sub-folder, I assume during import, and I really did not want to. Can you tell me how to get rid of this sub-folder so I have a single folder?

Tim’s Quick Answer: This task involves two basic steps. First you want to move the photos from the sub-folder into the parent folder. Then you want to remove the (now empty) sub-folder. Both of these tasks should be performed directly within Lightroom.

More Detail: To move the photos into the parent folder, you’ll naturally want to first navigate to the sub-folder that contains some of your photos. In other words, simply click on the name of that folder in the Folders list on the left panel in the Library module in Lightroom.

Next, make sure there are no filters applied to your images, so that you’re actually seeing all of the photos in the current folder. You can confirm this by selecting “None” on the Library Filter Bar, which can be made visible by selecting View > Show Filter Bar from the menu.

You can then select all photos in the current folder by choosing Edit > Select All from the menu. Then point your mouse at the thumbnail for one of the selected photos, and drag and drop to the parent folder in the Folders list on the left panel. You will see a dialog asking you to confirm that you want to move the photos on your hard drive, where you can click the Move button to finalize the task.

Once the process of moving the selected photos is complete and the sub-folder is empty, you can remove that sub-folder. To do so, simply right-click on the sub-folder and choose “Remove” from the popup menu.

This process of consolidating folders is covered in Lesson 7 from Chapter 2 in my course “Cleaning Up Your Mess in Lightroom”, which can be found in the GreyLearning video training library here:

http://greylearning.com/courses/mess

Larger Image Exports

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Today’s Question: Is there a way to adjust the export file sizes in Lightroom? I would like for them to be just a tad larger than what I’m currently getting.

Tim’s Quick Answer: You can most certainly specify pixel dimensions (image size) for photos you export from Lightroom, including creating an image that is larger than the pixel dimensions of the original capture. The options related to output size can be found in the Image Sizing section of the Export dialog.

More Detail: By default, when you use the Export feature in Lightroom to create a derivative image, that image will have the same pixel dimensions as the original capture you’re exporting. Obviously, in many cases you will want to change the pixel dimensions for that derivative image, such as for creating an image file for printing at a specific size.

If you turn on the “Resize to Fit” checkbox in the Image Sizing section of the Export dialog, you can specify the output dimensions you want to use. Note that in order to resize the image you are creating as part of this process, you need to have something other than “Original” or “DNG” selected from the Image Format popup in the File Settings Section of the Export dialog.

With the “Resize to Fit” checkbox turned on, you can then specify the output dimensions using the various options. The settings available allow you to choose from a variety of methods for describing the output size of the image being exported, the dimensions, and the unit of measure.

Note that there is a “Don’t Enlarge” checkbox that you can turn on if you want to make sure that the image you are exporting can’t be sized to dimensions that are larger than the original image. This will help ensure that, for example, you aren’t risking a reduction in image quality for lower-resolution source images. But if you leave that checkbox turned off you can specify dimensions that are larger than the original dimensions for the image you’re capturing, and the derivative image will then be sized based on the settings you have established.

I should add that here I’m referring to the overall pixel dimensions of the image file being created during the export process. The Quality setting also impacts the file size when you are creating a JPEG image from your source photo. That file size doesn’t relate directly to the potential output size for the derivative image, but rather to the overall quality. In other words, when it comes to producing derivative images for high-quality output I would focus on the actual pixel dimensions of the image, not on the file size (in megabytes, for example) of that image.

Offline Images in Lightroom

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Today’s Question: When I removed my hard drive from the laptop, the photos in Lightroom showed as “this file is missing”. Is this correct? Should the original source remain plugged in order to work in Lightroom? I do understand that I won’t be working on the original photo.

Tim’s Quick Answer: When the source images are not available on the computer you’re using for Lightroom, the images will indeed show as “missing”. There is no need to be alarmed, provided you know that the photos are only missing because your hard drive is disconnected. And even while the drive is disconnected, you can still update metadata and perform certain other tasks based on the Lightroom catalog.

More Detail: Because Lightroom employs a catalog to maintain information about your photos, you can work with your photos to some extent even when the source images are not available. For example, you can still view thumbnails and previews of your photos, because Lightroom generates those images for reference and maintains them with the catalog rather than with the source photos.

You can also update metadata, such as assigning star ratings, adding keywords, and other details, since that information is written to the catalog as well. If you generate Smart Previews for your photos you can even work in the Develop module and even export copies of your photos based on Smart Previews, all while the source files are unavailable due to the disconnected hard drive.

So, while there are situations where you need to have the source photos available to Lightroom, you can also perform a wide variety of tasks even when you have disconnected an external hard drive that contains your photos. This is one of the benefits of using Lightroom to manage your photos, as opposed to other software tools that do not employ a catalog.

Sensor Crop Factor

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Today’s Question: When using a camera with an APS-C sensor (that we will assume for ease of calculation has a crop of 1.5X). If there is a 50mm lens on that camera, the field of view is actually equivalent to 75mm lens because of the crop factor. So when I look through the viewfinder of the camera, am I seeing a 75mm view? When I take the photo, does the photo itself take on the 50mm or the 75mm field of view?

Tim’s Quick Answer: The “crop factor” determines the field of view actually seen by the image sensor for the current lens, and also impacts what you see through the viewfinder. So with your example of a 50mm lens on a camera with a 1.5X crop factor, the viewfinder would show an angle of view equivalent to a 75mm lens, and the captured photo would reflect that angle of view as well.

More Detail: I really wish we could start using “angle of view” rather than “focal length” to describe the behavior of a given lens. In the days of film photography the general use of focal length made some sense, since 35mm film was arguably the film format used most often. But even with film photography there were different film frame sizes, resulting in different behaviors for a given lens focal length depending on what film size was being used.

Today the situation is perhaps even more confusing, with digital cameras offering “full frame” 35mm sensor sizes, “cropped” sensors of various sizes, medium format imaging sensors, and more. Thus, there is either confusion about what the focal length of a lens really is, or about what the behavior of that lens will be.

For example, the primary lens on the iPhone has an actual focal length of around 4mm (which varies depending on the specific model of iPhone), but with the small sensor size of the iPhone that lens behaves like a lens with a focal length of around 30mm (again, depending on model). Talking about “effective” focal lengths is cumbersome and potentially confusing, and talking about actual focal lengths doesn’t clearly describe the behavior of the lens.

When you are using a sensor with a size that differs from a single frame of 35mm film, the behavior of the lens will be different than a lens with the same focal length would be on a 35mm camera. That is because the image circle projected by the lens is being “cropped” due to the smaller sensor. That change in the field of view is reflected by the image captured by the sensor, as well as by the viewfinder of the camera.

Note, however, that in many cases the viewfinder of the camera is not showing you a 100% view of the actual final image. Some viewfinders, for example, show around 95% of the total field of view being captured by the sensor. But in general you can expect the final image to be cropped based on the cropping factor of that sensor, and for the viewfinder to reflect that cropped view of the scene.

White Balance Settings

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Today’s Question: Can you address Auto White Balance (AWB) versus choosing Cloudy or Sunny or a given Kelvin temperature? AWB tends toward a blue cast. Is that fixed in the RAW file and can that be removed by changing temperature in Lightroom?

Tim’s Quick Answer: If you are shooting in RAW mode, the white balance settings you establish in the camera are purely metadata settings that establish the default adjustments when processing the RAW capture. Therefore, setting an optimal white balance compensation in-camera provides only a workflow benefit, not an image quality benefit. For JPEG captures, of course, the settings are fixed in the image, making those white balance settings important for JPEG capture.

More Detail: Current digital cameras generally do a very good job of determining a good setting for the white balance compensation, resulting in relatively accurate color in your initial captures. That is especially true under “normal” conditions, such as daylight. However, as noted in the question today, those settings are not always optimal. Fortunately, for RAW capture you have complete flexibility to refine your settings when processing the images after the capture, with no penalty in terms of image quality.

For RAW capture the white balance settings (generally a color temperature and tint setting) are simply metadata values. Those values will become the default settings for the RAW processing in Lightroom, Adobe Camera Raw, or other software. But you can refine those settings as needed to get the best final result, without any negative impact on the image quality.

In other words, from the standpoint of image quality, it doesn’t matter at all which setting you’ve used for white balance in the camera if you are shooting in RAW mode. No matter how inaccurate the settings are, you can adjust in post-processing.

Of course, from a workflow standpoint it is generally advantageous to have the color as accurate as possible in the initial capture. Thus, you may want to choose a specific white balance preset (such as Daylight or Cloudy). You can also dial in a specific Kelvin value to shift the balance between blue and yellow. For most cameras you’ll also find a Tint control, allowing you to make adjustments on a green/magenta axis. You can even use a “custom” option in many cases, where you photograph a gray card or other neutral target and use that image as the basis of an automatic in-camera white balance adjustment.

You might even find that setting the “wrong” white balance preset provides you with a good starting point. Using the “Cloudy” or “Shade” setting even on a sunny day, for example, will result in a photo that is a little warmer (more yellow) than you would otherwise achieve. Again, this isn’t critical for RAW captures, but may provide you with a workflow advantage, and a more pleasing image to review on your camera’s LCD display.

Still from Video

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Today’s Question: Is it possible in Lightroom to capture a still image from a video sequence that I have?

Tim’s Quick Answer: Yes, you can most certainly create an image in Lightroom based on a frame of a video clip. Simply pause the video on the frame you want, click the rectangular icon to the right of the time indicator presented below the video during playback, and choose “Capture Frame” from the popup menu. A JPEG image will be created for the current frame of the video.

More Detail: Creating an image based on a single frame of a video clip can obviously be helpful in terms of creating a still image from a video capture. However, capturing a single frame from a video can also be helpful for optimizing the appearance of a video.

You can adjust the appearance of a video using the controls in the Quick Develop section of the right panel in the Library module. You cannot, however, adjust the appearance of a video in the Develop module. However, you can apply adjustments to a still image captured from a video, and then apply those adjustments to the video itself.

The first step, of course, is to capture a still image from the video, as noted above. Then optimize that still image in the Develop module. Just keep in mind that only a small number of adjustments can be applied to videos within Lightroom. Those adjustments include White Balance, Basic Tone (Exposure, Contrast, Whites, Blacks, Saturation, and Vibrance), Tone Curve, Treatment, Split Toning, Process Version, and Calibration.

Once you have finalized the adjustments for the still image within the Develop module, you can save those settings as a preset. Then return to the Library module, select the video clip you want to adjust, and choose the preset from the popup in the Quick Develop section of the right panel. The adjustments you applied in the Develop module for the still image will then be applied to the video clip. You can then export a new copy of the video to create a final version with the adjustments applied.

Layer Mask Review

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Today’s Question: Thank you for your excellent presentations at the Chicago Area Photographic School this weekend. In reviewing my notes I realized I missed the “secret” to viewing the full-resolution layer mask in place of the image [in Photoshop]. Can you remind me of that technique?

Tim’s Quick Answer: You can view a layer mask in place of the full image by holding the Alt key on Windows or the Option key on Macintosh and then clicking on the thumbnail for the layer mask on the Layers panel. This will display the layer mask in place of the image, and you can return to the image by once again holding the Alt/Option key and clicking on the layer mask thumbnail.

More Detail: This technique of viewing the full-resolution layer mask can be tremendously helpful for evaluating the quality of your layer mask, and fixing any “blemishes” within the mask. For example, if you were painting on the layer mask but didn’t quite paint all the way into the corners of the image, it will be very easy to see the problem once you’re viewing the full layer mask. You can then work with that view enabled to cleanup your layer mask.

It can also be helpful to temporarily disable the layer mask so that the adjustment applies to the entire image, and then toggle back to having the layer mask enabled. By switching back and forth between having the layer mask disabled versus enabled, you can often spot areas of the image where the layer mask isn’t quite perfect. To toggle whether the layer mask is enabled versus disabled, hold the Shift key while clicking on the thumbnail for the layer mask on the Layers panel.

If you are a GreyLearning subscriber, you can view a lesson with more information about evaluating your layer masks within the GreyLearning video training library (http://www.greylearning.com). Simply go to the “Photoshop: Targeted Adjustments” course and view Lesson 6, which is titled “Evaluating the Layer Mask”.

PNG File Quality

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Today’s Question: I often use PNG files in compositing images, because they allow for transparent pixels. Are they like JPEGs in that every time you open, modify, then save the file, you lose image quality?

Tim’s Quick Answer: No, PNG (Portable Network Graphics) images do not have the same quality loss that can be a factor with JPEG images, because the PNG format supports lossless image compression to reduce file size. When you save a normal JPEG image, the compression applied always results in some loss of quality due to the type of compression used.

More Detail: The compression used for JPEG images is “lossy” compression, meaning some information is lost in the process of reducing the file size for a JPEG image. JPEG compression operates by simplifying the information within pixel grids (generally 16 by 16 pixels to a block). That compression causes a change in some pixel values, and can also result in artifacts such as a slight grid texture reflecting the grid used for compression.

Because the compression for a JPEG image is re-applied every time the file is saved, if there have been changes to the pixel values for the image it is possible to have a cumulative degradation effect for JPEG images that are repeatedly altered and saved. Simply opening a JPEG and re-saving it will not cause any further degradation, because the same algorithm would be applied to the same image data, resulting in the same result for the JPEG file.

The PNG file format employs lossless compression, so re-saving the image multiple times (even with changes) will not cause a further degradation of image quality.

I should hasten to add that while PNG images do include support for transparency, they don’t offer the flexibility of an image layer with a layer mask in Photoshop. The transparency of PNG images can most certainly be convenient when assembling images into a composite. However, if you have erased pixels to create that transparency, you can never get those pixels back in the PNG image.

Instead, I prefer to employ a layer mask in the original image, saving that result as a TIFF (Tagged Image File Format) image so that the layer mask is preserved. This approach enables you to employ the effect of transparency for a composite image, while still maintaining the ability to go back and alter which portions of the source image are actually visible versus hidden.