Ask Tim Grey

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.

Today’s Question: Thank you for the most recent educational piece on cleaning up the mess in Lightroom. I have Lightroom catalogs from Lightroom 3 through Lightroom CC. Some of the earlier catalogs show all of the photos as “missing” because in between one Lightroom edition and another I have either had a problem with my external hard drive or had to upgrade to a large external drive. I want to merge all of my catalogs. Must I first open them in Lightroom CC and map them to the current external storage drives or can I merely merge all of the catalogs since the current Lightroom catalog of 50,000+ photos already map to my hard external hard drives?

Tim’s Quick Answer: There is no need to reconnect “missing” folders in your Lightroom catalogs before you merge those catalogs. In many cases, in fact, it can be much easier to merge catalogs first, and then work to reconnect missing folders and photos across the entire “master” catalog you created in the process of merging multiple catalogs.

More Detail: If you have catalogs that have not been updated to the latest version of Lightroom, you do need to update those catalogs before merging them with your master catalog. To do so, simply choose the File > Open Catalog command from the menu in Lightroom. Lightroom will inform you that the catalog is from an older version of Lightroom, and will offer to upgrade the catalog for you.

Once all of your catalogs have been upgraded to the latest version of Lightroom, you can open your primary catalog and then use the File > Import from Another Catalog command to merge catalogs. This is possible even if some of the catalogs you want to merge contain missing photos.

Once you’ve merged all of your catalogs into a single master catalog, you can then get to work reconnecting any missing folders and photos, among other cleanup tasks.

All of these topics (and more) related to cleaning up problems in Lightroom are covered in detail in my latest video training course, “Cleaning Up Your Mess in Lightroom”, available with a subscription to the GreyLearning video training library (http://www.greylearning.com).

Today’s Question: This is a follow up to a question from last week [about merging catalogs in Lightroom]. I have two catalogs that I want to merge into one. Unfortunately, I have several photos that exist in both catalogs. Is there a way when merging two catalogs for Lightroom to alert you if a photo already exists in the catalog you are merging into?

Tim’s Quick Answer: When you merge catalogs via the “Import from Another Catalog” command in Lightroom, you will have the option to choose how to deal with any duplicate images. You can’t actually create duplicate copies in this case, and instead can choose whether you want to replace information in the destination catalog with information in the source catalog for the duplicate photos.

More Detail: If Lightroom detects that any of the photos from the source catalog are already contained within the destination catalog (your “master” catalog), you will see a notification indicating how many duplicate images were found within the “Import from Catalog” dialog.

If you know that the images in the destination catalog are your true “master” versions of all photos, you can simply choose the “Nothing” option from the Replace popup, and the duplicate images will be skipped in terms of the catalog merging process.

If the images from the source catalog are the more recent versions of your photos, you can choose to replace information in the destination catalog based on the information in the source catalog. You can choose whether you want to only update metadata (including Develop adjustments), or if you want to replace the original image files as well. In most cases, of course, the two source files would probably be identical, and so you could choose the “Metadata and develop settings only” option from the Replace popup.

If you’re not entirely sure which version of the duplicate photos is really the latest (or best) version of the photo, you can also turn on a checkbox that will create a virtual copy based on the second version of the duplicate images. That checkbox is labeled “Preserve old settings as a virtual copy”.

In addition, if you have a mix of RAW and non-RAW (such as TIFF and JPEG) images, you can choose whether you want to replace non-RAW captures only, updating only the metadata for RAW captures. That checkbox is labeled “Replace non-raw files only (TIFF, PSD, JPEG, PNG)”.

These options in the “Import from Catalog” dialog enable you to choose how to deal with duplicate images when merging catalogs into a single master catalog. The result will be a single copy of each image (or an image plus a virtual copy), so that you don’t have duplicate photos in your master catalog (at least based on the merging of catalogs).

Today’s Question: I know you don’t convert to DNG on import in your workflow, but for those of us that do I wonder if there are any advantages or disadvantages of also converting JPEG files (as from my phone) as well as RAW files?

Tim’s Quick Answer: I would say there aren’t any real advantages to converting a JPEG capture to the Adobe DNG file format, and there is certainly a disadvantage in the way of a file size that would be at least slightly larger for DNG as compared to the original JPEG.

More Detail: It would be reasonable to assume that converting a JPEG image to the DNG format would open up the possibility of applying “better” adjustments via Lightroom or Adobe Camera Raw, but that would not be an accurate assumption. You can already apply adjustments to JPEG images in Lightroom or Adobe Camera Raw, and there is no real benefit to converting a JPEG to DNG first.

In theory you might gain a slight advantage in terms of enabling a high-bit workflow and avoiding additional loss of quality and detail due to file compression. But in reality you are already starting with low-bit data, and with an appropriate workflow you don’t need to be worried with quality loss. Within Lightroom, for example, applying multiple adjustments in multiple stages does not have a cumulative negative impact on image quality.

While the DNG file format does employ lossless compression when converting RAW captures, yielding a DNG file that is generally around 20% smaller than the original RAW capture file, that does not hold true for JPEG images. Instead you will generally find that the DNG file is about the same size or possibly slightly larger depending on the settings for the original JPEG image.

So, on balance I would say there is no reason to convert JPEG images to the DNG file format. There are certainly reasons to consider DNG as a “replacement” file format for your original RAW captures (though as you note I am not a proponent of this approach), but not for JPEG images.

Today’s Question: I often begin optimizing an image by lowering the Highlights a bit, to eliminate any red “warning pixels” that Lightroom [or Adobe Camera Raw] might show me where I risk losing detail in the highlighted areas.

As I proceed, I may increase the Clarity a bit, to improve contrast and sharpness. But this often brings back the red warning pixels. (I think it may also bring back the blue warnings for loss of detail in the dark areas, but I’m inclined to worry less about that.)

Why does increasing Clarity result in possible loss of detail in the highlight areas?

Tim’s Quick Answer: Increasing the value for Clarity in Adobe Camera Raw or in Lightroom’s Develop module increases contrast, which can most certainly cause a loss of some detail in the brightest highlights or the darkest shadows in a photo. After increasing the value for Clarity, it is a good idea to check the values for the Whites and Blacks sliders (or simply view the clipping preview display) to determine whether detail has been lost, in which case you can adjust the values for Whites and Blacks to recover that lost detail. The same is also true for other adjustment controls, including the Highlights and Shadows adjustments, for example.

More Detail: The Clarity adjustment is, of course, a rather sophisticated adjustment. While the emphasis of this adjustment is to improve detail, that detail is improved by adding contrast within the photo. I think of this as an “intelligent” contrast enhancement, because it is applying an effect similar to sharpening to emphasize detail for the mid-tones in the image without having a significant negative impact on the highlights or shadows.

However, even with the sophisticated approach employed by Clarity, the additional contrast can cause some degree of detail loss in the highlights and shadows.

Especially if you have applied a relatively strong increase for the Clarity adjustment, it can be important to revisit the values for Whites and Blacks. In the question presented here, the clipping preview displays for shadows and highlights had been enabled, causing a red overlay on the image to indicate where highlights have been clipped and a blue overlay to indicate where shadows have been clipped. This option can be enabled by clicking on the triangle at the top-left (for shadows) and top-right (for highlights) of the histogram display on the right panel in both Lightroom and Adobe Camera Raw. You can also hold the Alt key on Windows or the Option key on Macintosh to enable a clipping preview while adjusting the Whites and Blacks (among other adjustment controls).

My general approach to applying basic tonal adjustments is to first set the white point by adjusting the Whites slider value with the aid of the clipping preview display. I then adjust the Blacks slider value, again with the clipping preview display. I’ll then fine-tune the overall detail and contrast using the Highlights and Shadows sliders.

At this point I will apply a Clarity adjustment based on an evaluation of the image. However, I will then revisit the Whites and Blacks values to ensure the peak values are still set appropriately.

In my view, it is always a good idea to revisit the Whites and Blacks values toward the end of your workflow for optimizing an image, especially for images where you want the brightest and darkest pixels to be near the white or black limit. The Clarity adjustment can cause an increase in contrast that causes a degree of clipping of highlights and shadows. The Highlights and Shadows sliders can also cause clipping.

So the point is, while we might generally think of the Whites and Blacks sliders as establishing the brightest and darkest values in a photo, other adjustment controls can also impact those pixel values. It can therefore be important to go back and forth between the various adjustments that relate to overall tonal values in the photo, to make sure you’re achieving the results you intend for the photo.

Today’s Question: I will be heading to the Smokey Mountain National park in late October and wanted to find out more about Variable Neutral Density (ND) filters. Originally I was thinking of getting a big stopper but then thought a variable ND with polarizer might be a much better choice. It looks less cumbersome to use and will also allow me to keep a lens shade attached.  What are your  thoughts or preferences about this?  Up until know most of my filter use has been confined to a Circular Polarizer and while I would like to keep things simple, I can really see the opportunities a strong variable ND filter can provide.

Tim’s Quick Answer: Variable neutral density filters offer considerable flexibility, and the option for a built-in circular polarizer filter only adds potential value. That said, my personal preference is to use a solid neutral density filter, because I find a solid rather than variable filters provide a more streamlined workflow. And I’m a huge fan of strong neutral density filters in terms of what they enable for creative effects.

More Detail: Due to the nature of variable neutral density filters, it can be a bit of a challenge to achieve a precise density value, which means it can be a bit of a challenge to find the right exposure settings. A little more trial-and-error tends to be required in order to find the right exposure settings based on the specific rotational position of the variable neutral density filter, and light angles play a role in this regard as well.

Because of this issue, as much as there is a tremendous potential benefit with variable neutral density filters, I prefer to use solid neutral density filters. When combined with an adjustment to the ISO setting on your camera, just one or two solid neutral density filters can provide great flexibility with a more streamlined workflow.

I discussed my specific approach to working with a solid neutral density filter in the July 2015 issue of Pixology magazine (http://www.pixologymag.com). The key is that with a solid neutral density filter you can simply establish your initial exposure settings, then add the filter and apply an adjustment to the exposure settings based on the density of the filter you’re using.

Even better, with a solid neutral density filter you can adjust ISO to improve your flexibility and reduce the number of filters you need to carry.

For example, I generally carry a ten-stop and a six-stop neutral density filter when photographing. I’ll also carry filters with a lower density value when shooting video, but that’s a different matter.

The ten-stop and six-stop filters are, of course, four stops apart in terms of density. If I am using the ten-stop filter but want to achieve the same results as would have been achieved with a six-stop filter without changing the shutter speed and aperture, I could raise the ISO setting to 1600 ISO. But, of course, that wouldn’t generally be necessary because I could simply switch to the six-stop filter or change my aperture or shutter speed values.

The point is, when using a solid neutral density filter you can adjust the ISO setting to create a result that is similar to what you might have achieved with a different neutral density filter or a variable ND filter. In my mind, being able to take this approach makes up for the lack of variability with a solid neutral density filter. And by using solid neutral density filters I’m able to avoid the trial-and-error issues that tend to be involved with the use of variable neutral density filters.

To be sure, there are some excellent variable neutral density filters available. I’m a big fan of the variable ND filters from Singh-Ray (http://www.singh-ray.com) for example. But my personal preference from a “workflow in the field” standpoint is to use solid neutral density filters rather than variable filters.