2:05 am0
Evaluating exposure via the Histogram
As you know, the image displayed on the LCD on the back of your camera is a poor tool to judge appropriate exposure—it cannot replace looking at your images on a proper display in a light-controlled environment. The trick, it is said, is to judge the exposure using the histogram—ideally applying what is known as the "Expose to the right" technique.
Moreover, as you also know, the image displayed on the LCD is not the raw file, it is a JPEG preview generated using the various parameters configured in your camera (white balance, saturation, contrast, etc.) Therefore, if your settings are such that the white balance is completely off the mark, for example, the image displayed will have a huge color cast. It's okay, since you know you'll easily be able to correct it later, because you're shooting raw.
What is less understood, on the other hand, is that the histogram itself is also not based on the raw data, but rather on that same JPEG preview! If you want to be able to judge the exposure using the histogram, how can you do it if the histogram is not based on the raw file? You can't!
...Well, let me re-phrase that: you can, but only up to a certain point.
What you should hope to achieve is a properly "exposed to the right" image—that is to say, an image that is exposed as far to the right as possible without clipping the highlights. That's a good thing, as we know that highlights hold more information than shadows, and what is nice about raw files is that they hold more highlights than what is possible when shooting JPEG. But how are we to know how far we can go if we base our judgement on a histogram that was built around a JPEG?
The idea is to use a set of parameters in the camera that will render the flattest JPEG preview, so as to generate the most generous histogram possible—regardless of the fact that it won't really matter in the end, as you are shooting raw and these settings are irrelevant to the final development of the image. If we were, for example, to use highly saturated colors and contrast to generate the JPEG preview (and, as a corollary, the histogram), we would be fooled into thinking that certain channels would clip before they actually do. Here is what you can do to render the most generous histogram possible:
- Use a bigger color space. If the camera allows you to use Adobe RGB (or even bigger) instead of sRGB, this will considerably extend the range of the histogram.
- Use minimal saturation and contrast. With Canon cameras (there are similar parameters in other brands as well, I am just not familiar with them), use a Faithful or Neutral "Picture Style", which will turn all the switches down.
- Use a white balance that is "close enough" to the actual lighting conditions—even if you intend to use something very different later, for effect. If you pick a Daylight white balance and shoot under tungsten light, for example, you might be fooled into thinking that the red/green channels are clipping before they actually do, as the JPEG preview will have a huge yellow color cast.
Needless to say, this will render a fugly image on the LCD, that will look completely washed out. Don't worry, you shouldn't be judging color/tint/saturation on the LCD anyway—do it for the greater good of a more reliable histogram.
Remember that the raw file still manages to contain more information than even this better histogram can display (because you will process the file using a bigger color space still, ProPhoto RGB), but at least you'll be much closer to the real thing.
1:24 am0
Keywording in Lightroom
Some precisions on keywording in Lightroom...
As you know, instead of adding tons of keywords to a single endless list and spending a long time trying to find them, a good approach is to create a hierarchy of keywords. You could have a simple tree of keywords such as this one:
Example of a hierarchical keyword list
Contrary to what you might have been told, when you select a child in a hierarchy, this automatically includes all of its parenthood in the list of keywords attached to the image—not only the child. The confusion comes from the fact that in the Keyword Tags list, the default option ("Enter Keywords") only displays the keywords that were entered/selected explicitly. If you pick the "Will Export" option, on the other hand, you will see the actual list of keywords that will be exported with the image. This reveals that, indeed, the whole hierarchy will be included:
Choosing "Will Export" reveals the true list of keywords exported
The only exception to this rule is the keywords that have been configured as "Private"—that is to say, that have their "Include on Export" option disabled (such as the root keyword "PLACES" in this example). Notice that, therefore, creating a hierarchy containing variants of a single word (such as plural forms Women/Woman) is not a good strategy, because selecting the child item would automatically include the other version as well.
The same way, you can avoid a lot of redundancy by using a hierarchy. If you were to create a sub-category for "kinds of trees", for example, you wouldn't need to call each tree "Palm Tree", "Oak Tree", "Elm Tree", etc., as the parent is called "Tree", and picking any one of them would already include the parent keyword "Tree".
Once you have keyworded your images, all you need to do to filter the images that were tagged with a specific keyword is to click on the arrow at the right of the keyword (it shows only when you hover the mouse pointer over the area):
Filtering by Keyword
As with any other metadata, these settings will be saved in the Lightroom Catalog, but contrary to what you might have been told, they can also be saved into the XMP sidecars or embedded into DNG, PSD or JPG files—the automation of which only depends on the settings of your Lightroom Catalog.
In the "Metadata" tab of the Catalog Settings, if you pick the "Automatically write changes into XMP" option, every time you make a change (be it keywords, develop parameters, crop, whatever), they will be saved into the actual files right away—not strictly kept inside the Lightroom Catalog. This means that even if you were to browse these files from within another compatible application (say, Adobe Bridge), you would indeed see all the metadata.
If you disable the "Automatically write changes into XMP" option, you can still force the settings to be saved to the files, but you have to do it manually. You can have Lightroom display whether the metadata have been saved or not as an icon in the Library Module:
"Metadata needs to be updated" icon
To trigger the update, either click on this icon, or select the files and use the "Control/Command+S" shortcut (this is helpful if you have a bunch of files that need updating).
2:12 am0
Small test prints
So you want to do a test print on a sheet, but you don't want/need to print a whole-page test.
Yes, you may resize and drag around the preview image in the "Print" dialog box from Photoshop, but it's really approximate—chances are you won't fully exploit the real estate. Yes, you may use the "Print" module from Lightroom, with a certain cell configuration, and fill in the blanks with a bunch of dummy blank images until your test image falls in the right spot, but it's kind of a hack—why won't the software allow to leave spots blank and drag a picture around on the layout is a mystery.
Here's a different approach. What I do is I create a new document in Photoshop, the size of the printable area of the test paper, at a good resolution (say, 300 ppi), and I split the page using guides according to how big I want the tests. I only need to do this once, because I save the file each time I'm done with a test. The advantage is that I know exactly where the next available slot for a test print is on the test paper, and because I have precise guides to help me, I can fully exploit the available space in each cell.
Test print layout.
Before printing, all I need to do is hide the layers of the previous test images, so that only the last one is printed. When the document is full, I delete the layers and change my test page.
Don't forget to write a little marker on the back of the test page, so you always feed it in the printer the same way!
2:56 amOff
Apertures for high-contrast ratios
It's been said that in order to be able to setup lights in high-contrast ratios (say, 16:1), the aperture f-stop used should be large enough to allow the fill to be mesured. The rationale behind this is that if the main light was setup for an aperture of say, f/4, then we wouldn't be able to read the fill, which would be four stops down.
In this case, this is flat out false, as f/4 -> f/2.8 -> f/2 -> f/1.4 -> f/1 is enough to do a reading (the light meter cannot display anything below f/1, a feat achieved only rarely in the history of photographic lenses in any case — altough you may be among the few who can afford a Leica Noctilux f/0.95).
But what if we wanted to use f/2 for the main, to produce a very shallow, dreamy depth-of-field, yet still maintain a 16:1 ratio?
The fact of the matter is that light intensity has no limitation in "dimness" — and the depth-of-field we want to achieve is more important than some mathematical restriction, after all! Although we must use an aperture our lens will ultimately be able to yield (for the exposure), it doesn't matter what "aperture" corresponds to the fill light, as long as it is enough stops below the main so as to maintain the desired ratio.
Since the light meter cannot display apertures below f/1, we can simply raise the light meter's (not the camera's!) ISO setting a couple of stops higher. For example, if we raise the light meter's ISO from 100 to 400, just for the sake of calculating the ratio, we gain two more stops that can be displayed. The main would register as f/4 (two stops higher than our desired f/2 at ISO 100, just like we expect), and our fill would register as f/1. No problem!
(Just remember to set the ISO back to 100 when you are done calculating your ratio...)
5:35 pm0
Direct reading using a Sekonic light meter
The default setting for how readings are displayed on the Sekonic Flash Master L-358 is in full shutter stops, with 1/10th aperture stops, as it was traditionally.
Various reading display settings on the Sekonic Flash Master L-358
For those who have learned their f-stops in the digital era, it usually makes more sense to talk of thirds of stops. If you want your Sekonic Flash Master L-358 to display direct readings, enable the DIP switch #3. Switch #4 determines if the reading will be in half or thirds of a stop.
Here's how my unit is normally setup:
DIP Switches on my unit
4:49 pm0
LightRoom Print Job
The Print Job panel of Lightroom's Print module needs some explanation, because as it is, it looks fairly simple and straightforward, but it is also quite opaque about what each parameter is actually doing.
Lightroom's Print Job panel
Print to. In this drop down menu, you can decide to export the layout to a JPEG file instead of sending it to a printer. Instead of simply sending the image content to a file (as the Export function would do), this exports the whole page—that is, the image as well as the white border, the watermark, etc. This might be useful if you're sending the file to a professional print service—check with them about the appropriate parameters to use for resolution and color profile (a common requirement is a 300 ppi sRGB).
Draft Mode Printing. This mode is mostly self-explanatory, yet what needs to be said is that the image data used for the print is not extracted from the original files, but rather taken from the (lower quality) image previews contained in the catalog. Therefore, depending on the size of the previews you have configured Lightroom to generate, the quality of the draft print will be affected. (This might not be a problem if you are printing contact sheets, for example, since then the images are pretty small to begin with.) The advantage though, is that you can print in Draft Mode even if the original files are offline—all you need is for the images to have been cataloged.
Print Resolution. This parameter defines whether to resample the image data to a given resolution or to use the native resolution of the file (whatever is necessary to print the image to the desired size). Indeed, according to Adobe's documentation, checking that box and setting a resolution will "resample the image data if needed, depending on the print resolution and the print dimensions". It then goes on to say that "To use the native resolution of the photo (as long as it isn’t lower than 72 ppi or higher than 480 ppi), deselect Print Resolution."
As it's been said before, the general wisdom tells us that we do not want to resample our images if we're outputting the job to a printer (unless the resolution reaches extremes), so we should usually leave this box unchecked.
Now, this is a very important parameter that has seen its behavior change with each new version of Lightroom. Back in the original Lightroom 1.0, there was no way to disable the resampling, and this left many users unsatisfied—you should definitely update to at least 1.1 if you are in this situation, since Adobe swiftly addressed the issue and it was now possible to disable it.
But then in Lightroom 2.0, the whole output sharpening apparatus was rewritten as a result of a collaboration with PixelGenius (the guys behind PhotoKit Sharpener, the popular sharpening solution based on Bruce Fraser's seminal work on sharpening), and it was later found that the optimal result was not necessarily obtained by systematically using the native resolution.
Here's the crutial part:
- If you've performed the output sharpening on an image outside Lightroom (such as in a round trip to Photoshop), you definitely will want to use the native resolution—you do not want to resample an image that has already had its output sharpening carefully applied.
- If you're working on a raw file (or any other file that has not yet had output sharpening applied) inside Lightroom and you're using a version prior to 2.0, you also do not want to resample the image, as you will likely lose some quality, for reasons that have been discussed before.
- If you're working on a raw file inside Lightroom version 2.0 or more, then tests have seemed to indicate that you could achieve an arguably better result by upsampling the image by about 50%—that is, if the native resolution is, say, 240 ppi, you'll want to resample the image to 360 ppi. This remains true only if you are combining this with output sharpening (which will be discussed next) and only if you are upsampling—it remains true that you should use the native resolution rather than downsampling the image.
Print Sharpening. This parameter defines if Lightroom is to apply output sharpening to the image (which is not the same thing as capture sharpening, applied elsewhere in the Develop module, nor creative sharpening, applied locally). If you have already performed output sharpening on a file, you won't want to use additional sharpening and you'll leave this box unchecked. Otherwise, you'll definitely want to add some output sharpening.
According to Jeff Schewe, in relation to the output sharpening in Lightroom 1.x: "Low and Medium are useless—I can't see the result—and High is almost worthwhile." In other words, when using Lightroom 1.x, you'll likely want to use the "High" setting to apply a meaningful amount of output sharpening—or, better yet, perform your output sharpening in Photoshop before going to the print module.
In Lightroom 2, on the other hand, the output sharpening algorithm has been considerably improved, so as long as you've applied an appropriate amount of capture sharpening in the Develop module, using the "Standard" setting will likely be a good choice most of the time, making things really, really simple.
Naturally, sharpening is applied differently depending on the paper type used (if the paper has a coating or not), so you'll need to specify it under Media Type. According to the documentation: "Matte includes watercolor, canvas, and other nonshiny types of paper. Glossy includes luster, semigloss, photo gloss, and other shiny types of paper."
To finish off, don't forget to disable the printer color management and select the appropriate profile for the printer/paper/ink combination you're using. The "Relative" rendering intent is appropriate most of the time, but for critical work, you might want to go perform some soft proofing in Photoshop before deciding.
As for the 16-bit output, if your printer driver supports it (get the latest version), you should certainly use it. Even if the driver doesn't support it, if you're not sure, using the 16-bit mode won't do any harm—it'll just be useless and might slow down the spooling a bit.
2:19 am0
Resampling images for print
Regardless of the time an image takes to be spooled to the printer, resampling an image (i.e.: changing its pixel size using interpolation) is to be avoided, as resampling an image is detrimental to its quality.
The bottom line is this: if the native size of the image allows you to print using a resolution between 180 and 480 dpi, and if proper sharpening has been applied (considering the destination of the print, its resolution, etc.), you should let the printer do whatever interpolation is required.
Only if you intend to make a print so large that you have less than 180 dpi available, or if you intend to make a print so small that the resolution is above 480 dpi, should you resample the image. If you need to resample, keep this in mind:
- It is arguably preferable to resample by doubling (200%) or halving (50%), rather than using intermediate steps.
- For up-resing, the preferred algorithm is "Bicubic Smoother" — although you will then have to add a significant amount of sharpening.
- Output sharpening should always be applied after resampling.
For a detailed discussion on the topic of sharpening, refer to the Real World Image Sharpening book series. The Luminous Landscape also has video tutorials on the topic, notably chapter 12 of "From Camera to Print".
1:57 am0
Cancelling color casts
Color casts (overall color drifts) are avoided by using the appropriate white balance setting at capture time (the most accurate of which is a "custom" white balance), or by including a neutral reference in the picture for adjustment in post-production (such as a WhiBal).
Unfortunately, we don't always have time to follow this procedure, so we must often correct color casts arbitrarily in post-production. The problem is that it is not always possible to find parts of the subject which are of a neutral color, with which we can cancel the color cast. And even when we think something is neutral, chances are it is not really (who says this white wall was really pure white — it probably was yellowish!)
The quick and dirty solution is to pick something "close enough" as the reference for setting the white balance, and to adjust, subjectively, until we get something that looks more natural (completely neutral images often look unrealistic, too cold or too warm).
There is a trick to fix color casts in Photoshop which involves:
- Duplicating the image's layer;
- Applying an "Average Blur" filter on that layer (this reveals the overall color dominance);
- Inverting that layer (to obtain the opposite color of the cast, the one that neutralizes it);
- Changing the "Blending Mode" of that layer to cancel the color cast of the image.
Obviously, this trick can only get you so far — you still have to judge by eye what "feels right", by adjusting that layer's opacity, to apply more or less of the cancelling.
That being said, the procedure can be optimized to be executed faster and to render smaller files. Here's the trick. With a Smart Object of the image:
Apply an "Average" blur Smart Filter:
Create a "Curve" Adjustment Layer and use the "Gray Point" eyedropper anywhere on the image:
In a single click, you have set the three color curves to perfectly neutralize the average color of the image!
Color cast cancelling Curve Adjustment Layer
To finish up, simply delete the "Average" blur Smart Filter, which you don't need anymore:
You end up not with a new full-size layer of a fixed color (taking up disk space uselessly), but with a much more flexible "Curve" adjustment layer.
2:00 pm0
Duplicating layers is oldthink
Back in the day, it used to be common practice to duplicate the final image layer to apply, for instance, output sharpening. The rationale was that this way, the original image would be preserved — the sharpening would only be applied on the duplicate, which could be thrown away at will.
Duplicate layer used for output sharpening
This also had the unfortunate effect of creating much larger files, as much more information would be required to save the two distinct layers (with all the downsides of larger files):
File size dramatically increased by using a duplicate layer
Luckily for us, later versions of Photoshop have provided a feature called "Smart Objects", allowing us to work with any layer (or any group of layers, of any type) in a non-destructive manner. Smart Objects can be transformed, warped, or have filters applied upon (called "Smart Filters"), without altering the original data. Sounds familiar?
Unsharp mask applied as a Smart Filter on a Smart Object
What's even better is that Smart Filters can later be edited — much like adjustment layers — or deleted altogether. Notice that this time, the file size is basically unaffected:
When using Smart Filters, the file size is basically unaltered
The Smart Object itself can also be edited, if need be. Double-clicking on it will open it as a new document containing the original layers, and all changes saved will be applied to the Smart Object that encapsulates the original layers. Even raw files can be turned (embedded) into Smart Objects: double-clicking it brings up Camera Raw and allows the user to further work on the image, without ever losing the flexibility of the raw format. (To open a raw file as an object, in Camera Raw, press the Shift key to turn the "Open Image" button into an "Open Object" button.)
If you'd like to apply a Smart Filter only to certain regions of the image, you can use the layer mask that is automatically provided when they are used.
If you prefer to work with the famous "High Pass" sharpening method, for example, you may be wondering if you'll be able to get rid of duplicate layers, as the effect used to be applied on a duplicate layer that later had its blending mode changed. No problem! In that case, you would use the "High Pass" Smart Filter on the Smart Object, and then open the "Edit Smart Filter Blending options..." dialog:
Blending options of a Smart Filter
You can there set the blending mode and opacity of any Smart Filter individually.
You can even use many filters simultaneously, and change the order in which they are applied:
Applying multiple Smart Filters
2:30 am0
Sensor cleaning dos and don’ts
Contrary to what you might have heard, there are some methods for cleaning sensors that are an absolute no-no:
- Never use "Dust-Off" or other regular compressed air products. These products are made to clean keyboards, computer cases and such, but not digital camera sensors. They are liquid-based and may spray harmful particles on your sensor. (If you're into compressed air, specialized compressed CO2 products are available that do not risk blowing harmful particles onto the sensor.)
- Never expose the sensor using the "bulb" exposure mode. There is a dedicated feature in your camera that reveals the sensor. First off, the "bulb" mode would not prevent you from using it when the battery is near depletion, which could surprise you by slapping the mirror back down while you're doing your thing, risking damage. Secondly, the dedicated sensor-cleaning feature reveals the sensor, but does not actually record an image. Unlike the "bulb" mode, the sensor is not electrically charged, which means that it won't attract more dust. And finally, using the sensor cleaning feature frees your two hands!
So then, which methods are adequate? Many, but it depends on the severity of the problem.
- Blowing air onto the sensor usually removes the most obvious particles. This is the less intrusive method, as nothing but air touches the sensor. As said previously, do not use regular compressed air products — a simple blower will do. Be careful though: some cameras are constructed in such a way that blowing air into the mirror box might cause some dust to lurk into the prism assembly, which will require servicing to get removed!
- For a thorough removal of dust specks, a static-charged brush (such as one made by VisibleDust) will do a very good job. This method requires touching the sensor, but there is no real danger, as these brushes are very delicate. Be careful though: the brush needs to remain immaculate and cannot be cleaned! When locating dust specks, remember that the image you see on your LCD was actually upside-down on the sensor!
- For stains that are not simple dust — such as moisture or other liquids — you'll need to use sensor swabs (of a size appropriate for your camera's sensor) with a special cleaning fluid (of a nature appropriate for your camera's sensor), such as Eclipse. This is the most intrusive method, but is sometimes required for tough stains.