Category: Ask Tim Grey

Today’s Question: This may be a bit of a stretch, but… The subject of blend modes reminded me of a technique that I think involved a blend mode [in Photoshop] to determine whether the frames of a panorama are aligned well. I know there are automatic options for assembling composite panoramas, but I like to put them together myself. Can you remind me of the blend mode option, if I’m even remembering these few details correctly?

Tim’s Quick Answer: It is indeed a blend mode that provides the feature you’re looking for in Photoshop, where you’re able to see the degree to which the pixels in two overlapping layers actually match. That blend mode is the Difference blend mode.

More Detail: To use the Difference blend mode for evaluating the alignment of two image layers, simply change the blend mode for the upper image layer on the Layers panel. So, you can click the thumbnail for the upper of the two layers you want to compare, to make sure that layer is active. Then click the popup at the top left of the Layers panel (the popup has the default value of “Normal”) and choose Difference.

With the Difference blend mode, any pixels that are an exact match on the upper and lower layer will appear as black. Any pixels that aren’t an exact match will appear as a color that differs from black to the degree there is a “mismatch” between the pixels.

In other words, when using the Difference blend mode for this purpose, your goal is to have as much black in the image as possible. You can move the image layers, resize the image layers, transform the image layers, and more, in order to achieve the best alignment possible.

While I do find that various software tools (including Photoshop) do a great job of automatically assembling and aligning the individual frames for a composite panorama, I also find the Difference blend mode to be tremendously valuable when I choose to take a “manual” approach for any reason.

Today’s Question: How do I know when I should be capturing several images for an HDR (high dynamic range) instead of just a single exposure?

Tim’s Quick Answer: Conceptually, whenever the histogram display for a single exposure shows clipping at both the black and white ends of the histogram (or significant clipping at one of the two ends), you might want to capture bracketed exposures to possibly assemble into a high dynamic range (HDR) image.

More Detail: With practice, of course, you can learn to anticipate when the overall contrast (or dynamic range) of the scene you are photographing is significant enough that a single exposure won’t be able to contain the full range of tonal values in the scene. The limitations in terms of dynamic range vary from one camera to the next, but over time you will develop a sense of when you’re near (or past) the limitations of your camera.

Of course, just because the dynamic range of the scene is beyond the capabilities of your camera to record in a single capture doesn’t mean you should create an HDR image. A photo with clipping of detail in the darkest shadows could simply be a dramatic photo, and a photo with clipping of highlights could simply be a very nice “high key” photo.

That said, my approach is to capture a sequence of bracketed exposures whenever I know (or my camera’s histogram display tells me) that the full dynamic range of the scene can’t be captured with a single photograph. This provides the flexibility of deciding later whether I want to create an HDR image or simply work with the best of my various exposures.

So, there is an element of experience in terms of being able to anticipate when the dynamic range of a scene exceeds the capabilities of your camera. There is also an artistic decision to be made here in terms of how you will interpret the scene. But in general I prefer to have bracketed exposures whenever the scene has a high dynamic range, so I have more flexibility when processing my photos later.

Today’s Question: Is there a difference between the Overlay and Soft Light blend modes in Photoshop? I see some people using one versus the other with the same basic techniques.

Tim’s Quick Answer: The Overlay and Soft Light blend modes are both “contrast” blend modes that enable you to achieve both a brightening and darkening effect with an underlying image at the same time. The effect of both is essentially the same, with the difference being that the Overlay blend mode creates a somewhat stronger effect than the Soft Light blend mode.

More Detail: The first three categories of blend modes in Photoshop enable you to apply a darkening effect (with Multiply being the first of these blend modes), a lightening effect (with Screen being the first of these blend modes), or both (with Overlay being the first of these blend modes).

I refer to the blend modes that can both lighten and darken as the “Contrast” blend modes. There are a variety of situations where you might use a contrast blend mode, such as dodging and burning by painting onto a separate layer or reducing haze and enhancing detail with the “High Pass” sharpening technique.

With a contrast blend mode, any pixels on the layer to which you have applied the blend mode that are lighter than middle gray will have a lightening effect on the underlying image. Any pixels that are darker than middle gray will have a darkening effect on the underlying image. So if you have both light and dark areas in the layer you’ve applied the contrast blend mode to, you’ll brighten some areas and darken others, leading to (generally speaking) increased contrast.

The Overlay blend mode simply applies a stronger effect than the Soft Light blend mode. Thus, some photographers prefer one over the other. I, for example, prefer the Overlay blend mode because it provides a stronger effect.

It is important to keep in mind, however, that with many of the techniques where you might employ a contrast blend mode, you’re going to reduce the Opacity setting for the layer to which the blend mode is applied. Therefore, the final effect can be the same with either Overlay or Soft Light, with the only difference being the specific Opacity setting you use to achieve the final effect.

In general you can think of the Overlay and Soft Light blend modes as being interchangeable. Just keep in mind that the Overlay blend mode provides a stronger contrast effect than the Soft Light blend mode.

Today’s Question: I’m new to Facebook, and was wondering when you post images from Ligthroom directly to Facebook, can you have multiple pictures in one timeline event? I see you can post to photo albums, etc. But each image is a separate timeline event. With some posts I would like to group more than one picture to a single timeline event.

Tim’s Quick Answer: Yes, you can publish multiple photos from Lightroom to Facebook as a single event on your timeline. You just need to create a new collection for that task, and then publish all of the photos in that collection at the same time. Facebook will then include all of the photos published as part of that process in a single timeline event.

More Detail: You first, of course, need to authorize Lightroom to access your Facebook account, which you can do by clicking the “Set Up” link to the right of Facebook in the Publish Services section of the left panel in the Library module in Lightroom.

Once you’ve configured Lightroom to be able to access your Facebook account, the next step is to create a collection for publishing a group of photos to Facebook. You can start by selecting the photos you want to include on that collection. For example, you might filter your photos so you can only see those you’re interested in sharing on the Filmstrip. Then select the specific photos you want to share to Facebook.

With those images selected, right-click on the Facebook item in the Publish Services section of the left panel and choose “Create Collection” from the popup menu that appears. In the Create Collection dialog, configure the settings for this collection, including the details in the “Facebook Album” section, such as the “Album Name”. When you’re finished configuring these settings, click the Create button to actually create the collection.

Finally, viewing the new collection under Facebook in Publish Services, and with the Grid view enabled (which you can do by pressing “G” on the keyboard if you were in the Loupe view), click the “Publish” button toward the top-right of the images in the Grid view display. This will cause all of the photos to be published to the Facebook album you specified, and once the process is complete the publication of those photos will appear as a single timeline event.

Note that as the several photos are published, you will initially see an event for a single photo, but that will update as each photo is published so that you still only have a single timeline event for all of the photos you just published.

Today’s Question: [Using a separate layer for image cleanup work in Photoshop, as covered in the September 7th edition of the Ask Tim Grey eNewsletter] would all be great except for the final critical step, sharpening. I don’t see any way around making a second file, or double BG layer, and still get to a suitably sharp image.

Tim’s Quick Answer: This is exactly why I perform sharpening as part of a specific “output workflow”, where I create a copy of my master image, flatten that copy, resize for the intended output size, and sharpen the image. Thus, the sharpening is being applied to a flattened (and resized) copy of the master image. In most cases I don’t even need to save this duplicate output file, because any future output will be created based in the “master” image file that still contains layers.

More Detail: Today’s question is a follow-up to the question I addressed in the September 7th edition of the Ask Tim Grey eNewsletter, which related to the use of an empty layer for image cleanup work. One of the key benefits to this approach is that the file size is not significantly increased the way it would be if you instead created a copy of the full Background image layer.

By taking this approach, I am able to retain all of the layers I used to produce the final image as part of my “master” image file, without unnecessarily increasing the file size. My approach is to never flatten this master image, always preserving the layers for maximum flexibility should I decide to make any changes to the image.

Of course, while I never flatten my master image, that doesn’t mean I won’t flatten a copy of that image for purposes of my output workflow. As noted above, this workflow involves making a copy of my master image (via the Image > Duplicate command on the menu). I can flatten the copy in the process of creating this duplicate by turning on the “Duplicate Merged Layers Only” checkbox in the Duplicate Image dialog. I will then resize based on the intended output for the image, and apply sharpening (generally using the Smart Sharpen filter). This results in an image that has been optimized for the specific output size and output conditions, based on (for example) the print I plan to produce.

If I think I’ll likely want to print the same image at the same size in the future, I could save this derivative image with a reference to the output size in the filename. But personally I don’t tend to need to re-print the same image at the same size very often, so I generally don’t save the derivative image. Instead, I simply return to my original master image whenever I need to produce additional output for that photo.

Today’s Question: You mentioned capturing video with your digital SLR at 30 frames per second with a 1/30th of a second shutter speed. But that means the camera is constantly capturing frames. How is it that the buffer never gets full the way it does with still captures?

Tim’s Quick Answer: The short answer is that video is captured at a much lower resolution than the camera is capable of for still images, and so it is possible to capture video at a high frame rate for an extended period of time without filling the memory buffer in the camera.

More Detail: Let’s assume a somewhat typical (or at least popular) camera that is capturing images with a 22-megapixel sensor. That would involve maximum pixel dimensions for a still image of (for example) 5,760 pixels by 3,840 pixels. At a frame rate of six frames per second, the camera is capable of capturing 17 images before the buffer is full and capture speed will slow.

However, that full buffer represents 17 RAW captures of 22 megapixels. By contrast, full 1080p high definition (HD) video is “only” 1,920 pixels by 1,080 pixels, which is the equivalent of about 2 megapixels. In other words, there is a lot less information being captured when recording video rather than full-resolution still captures, and so you can capture many more frames without filling the buffer.

In general you will find that a digital camera that offers full HD video recording will be able to capture video continuously without filling the buffer. Of course, there are other factors to consider when it comes to recording video for and extended period of time, including overall file size, heat buildup, and other considerations. But you generally won’t need to worry at all about the buffer limitation of your digital SLR when you’re capturing video rather than still captures.

Today’s Question: What is the difference between Opacity and Flow? I think I halfway understand this, but would sure like to hear your explanation.

Tim’s Quick Answer: Opacity is the degree to which a color you paint with will be opaque versus transparent, while Flow relates to whether there will be a fade-in and fade-out effect relative to opacity for each brush stroke. These options are available in various contexts (though all related to painting) within Photoshop, Lightroom, and other applications.

More Detail: I think it can be helpful to use airbrush painting as an analogy for understanding Opacity and Flow. With an airbrush you are spraying paint onto a surface. Think of Opacity as the degree to which the paint is “watered down”, which determines whether the paint will completely cover the surface you’re painting to or allow that surface to “show through” a relatively light coating of paint.

The Flow setting relates to how fast the paint is being sprayed out of the airbrush. If the paint is flowing quickly (a high setting for Flow), even if you move the airbrush extremely fast across the surface the paint will have a high effective opacity. If the paint is flowing slowly (a low setting for Flow), you are better able to vary the effective opacity along a paint stroke by varying the speed at which you move the airbrush across the surface.

So, Opacity is your primary control for determining whether your brush strokes will completely cover up underlying pixels or blend somewhat so the underlying pixels still show through. Flow is related, in that it affects the rate at which the color will be applied as you’re painting.

In other words, with Flow set below 100%, when you paint with the brush the effective opacity will initially be lower than what the Opacity is actually set to, transitioning to the full Opacity setting. Similarly, when you stop a brush stroke there will be a transition from the set Opacity to a lower value.

This explanation, of course, probably doesn’t leave the impression that the Flow setting is especially helpful. But that’s because there are two additional considerations you’ll want to take into account when making use of (or evaluating the value of) the Flow setting.

To me the real value of the Flow setting isn’t the Flow setting all by itself, but rather the Flow setting in the context of painting with a pressure-sensitive device such as a tablet and stylus. When using a pressure-sensitive device (with the Fade Jitter setting set to “Pen Pressure” on the Brushes panel in Photoshop, for example), the amount of pressure you apply with the stylus while painting determines the behavior of the brush strokes based on the Flow setting. In other words, you can use the pressure you apply when painting with the stylus to control the Flow behavior. That means instead of a fixed transition from a reduced opacity to the value based on the current Opacity setting, you can vary the transition so your stroke Opacity (and the transition between opacity effects) varies.

Another option in Photoshop is the Airbrush feature. This allows the opacity of your brush stroke to build up, based on the Flow setting. So, with a low Flow setting and a relatively low Opacity setting you can paint a quick brush stroke to paint with a low effective opacity. If you slow down (or stop) the movement of the brush the paint will “build up”, creating greater effective opacity for that portion of the brush stroke.

If you think about the Opacity and Flow settings in the context of a real-world airbrush (or can of spray paint), I think it will be easier to understand these settings in software such as Photoshop and Lightroom.

Today’s Question: Which brand of Neutral Density Filter do you use? Is it the B+W 77mm 3.0 ND MRC and the equivalent 6-stop neutral density filter?

Tim’s Quick Answer: For my photography I generally carry a 10-stop (for dramatic photographic possibilities) and a 6-stop (for slightly faster shutter speeds) neutral density filter. I typically use filters from B+W, as I have found them to provide excellent quality at a competitive price.

More Detail: A ten-stop neutral density filter (with a density value of 3.0) provides excellent creative possibilities in your photography. With a filter this strong you can achieve 30-second exposures even during full daylight, and you can achieve longer exposures during darker (or night) conditions. With a ten-stop neutral density filter I find I can produce images that would otherwise be impossible, and I have a great deal of fun in the process.

For situations where I don’t need quite as long an exposure time (and I don’t want to increase the ISO setting just to get a faster shutter speed while using a 10-stop neutral density filter) I also carry a 6-stop filter. If I only carried the 10-stop filter, I would need to raise the ISO setting to 1600 to achieve the same shutter speed as the 6-stop filter while using the 10-stop filter. So I find it helpful to have an “extra” filter in my bag to help avoid the need to raise the ISO setting too much.

Because I also shoot a lot of video, I carry a 2-stop neutral density filter in addition to my 6-stop and 10-stop filters. This is primarily for situations where I need just a little bit of help to achieve a 1/30th of a second exposure based on video captured at 30 frames per second. Sometimes I only need 2-stops of density to get to the target shutter speed for video, and with video in particular I try to avoid raising the ISO setting. So, I carry a 2-stop neutral density filter in addition to the other two filters when I anticipate capturing video along with stills during a photo outing.

You can find all three of the neutral density filters I reference here using the following links:

10-Stop Neutral Density Filter: http://timgrey.me/nden10

6-Stop Neutral Density Filter: http://timgrey.me/nden6s

2-Stop Neutral Density Filter: http://timgrey.me/nden2stop

Today’s Question: I’ve been making a copy of the Background image layer in Photoshop when I need to use the Clone Stamp or Healing Brush tools. I think I heard somewhere that this isn’t necessary, and causes the files to get much bigger. But if I don’t want to replace my “original” pixels, how can I avoid making a Background Copy layer?

Tim’s Quick Answer: I am a big advocate of a non-destructive workflow that employs adjustment layers and additional image layers as needed, but I also am not interested in having my image files grow any larger than is necessary. Thus, instead of creating a Background Copy layer for image cleanup, I recommend creating a new empty image layer for this purpose.

More Detail: When you create a copy of the Background image layer in Photoshop, you are doubling the base file size for the image. For example, let’s assume you started with an image that didn’t have any layers beyond the Background image layer, and that the file size was 25MB. As soon as you create a Background Copy layer, the image size (assuming no compression or other factors) would now be 50MB.

When you create a new empty image layer, the file size remains virtually unchanged, at least initially. There is a slight change because there is some additional information being preserved in terms of the presence of the new layer, but that new layer doesn’t contain any pixels and so it is not adding significantly to the file size.

So, when I am going to perform image cleanup work, I will click on the Background image layer (or the top-most image layer if there are multiple image layers), and then click the “Create a New Layer” button (the blank sheet of paper icon) at the bottom of the Layers panel. This will create a new layer that is below any adjustment layers and above any image layers, and thus is ready to be used as an image cleanup layer.

You can then use any of the image cleanup tools, making sure to use the appropriate option to enable you to work across multiple image layers. For example, with the Clone Stamp tool you could choose the “All Layers” option from the Sample popup on the Options bar, and turn on the option to ignore the effect of adjustment layers. With the Spot Healing Brush tool you could simply turn on the “Sample All Layers” checkbox on the options bar. Then make sure your new empty image layer is the active layer, and then perform your image cleanup work there.

By taking this approach, the layer you created for image cleanup work will only contain the actual pixels you used to remove blemishes from the photo. That, in turn, means the image file size will not increase significantly, especially compared to creating a full copy of the Background image layer.

I also, by the way, highly recommend renaming the new layer you created for image cleanup, to help avoid confusion later. You can rename a layer by double-clicking the name of the layer on the Layers panel, typing a new name, and pressing Enter or Return on the keyboard to apply the change.

Today’s Question: We are in the constant midst of downsizing image space on our server. I’m being asked to save all of my files to 3MB. It there a way to batch process files in my folders [using Photoshop CS6]? I have larger files (originals) backed up on external drives and also DVDs.

Tim’s Quick Answer: Photoshop actually includes an Image Processor tool that makes it very easy to batch process images to create files of different file types or different file sizes (based on pixel dimensions and/or compression). I recommend using Adobe Bridge in this case, selecting the images you want to process and then choosing Tools > Photoshop > Image Processor from the menu to get started with the batch processing.

More Detail: In this case you might want to save the images on the server as JPEG images, on the assumption that file size is a higher priority than image quality in this situation. This is mitigated by the fact that you have the original captures backed up in another location, so the files on the server can be thought of as working copies. You can always revert to those original captures if you need a file of higher resolution or quality.

In the Image Processor dialog I recommend using the “Save in Same Location” option. This will not cause the source images to be over-written, and in fact the files won’t exactly be placed in the same folder. Instead, the resulting images will be placed in a subfolder below the current folder, with a filename based on the file type you choose.

You can then turn on the appropriate checkbox for the type of file you want to save as a result of this batch process. In this case I would probably opt for the “Save as JPEG” option. You can then adjust the settings for the JPEG images, including the Quality setting and the “Resize to Fit” option that allows you to reduce the pixel dimensions for the photos.

For a JPEG image, using pixel dimensions of around 3,000 by 2,000 pixels with a moderately high Quality setting (perhaps about a value of 8) will generally produce image files that are below 3MB in size. The specific size of each image will depend on the relative complexity of the image itself, as that impacts the degree to which compression can reduce the file size.

Once you’ve established the settings for the Image Processor, click the Run button and the photos you selected will be processed. You can then archive the original versions of the photos on the server, and move the images created by Image Processor into their location.