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 pm0
Flat images on the web
Still following up on the working color space post...
It is sometimes said that images using the ProPhoto RGB or Adobe RGB workspace placed on the web will look flat because the browser converts the images to sRGB, resulting in a poorer rendition.
This is not what is going on.
As it has been said before, converting from a larger workspace to a smaller workspace is rarely a big deal, and is only really an issue for colors that fall out of the gamut of the destination workspace. If it was the case that browsers converted all images to the sRGB workspace, the effect would most of the time be very subtle. Converting an average image from ProPhoto RGB to sRGB does not result in an obviously globally flat-looking image. It would be a very wasteful, useless exercice in deterioration if this is what browsers did.
The problem with flat ProPhoto RGB/Adobe RGB images on the web is that not all web browsers (or not all versions of a given web browser) perform color management. Web browsers that do not color manage will simply presume that images are described using the sRGB workspace, regardless of the workspace they are really using. (Again, the following scale is arbitrary and is simply used to explain the concept.)
The ProPhoto RGB scale as presumed to be sRGB
If the image was using the ProPhoto RGB workspace, from the point of view of the sRGB workspace, all of its colors represent flatter colors. No conversion involved at all, it is just a matter of an erroneous presumption.
There is no question that you should use a browser that does proper color management if you can. To see if the browser you are using performs proper color management, visit this web page.
Nevertheless, even if you are using a browser that does proper color management, it certainly does not mean that other people do. You should always convert your images to sRGB before posting them on the web to reach a larger audience, as this is the common denominator.
12:30 pm0
Color profile conversions
Following up on the previous post, it should be added that converting from one profile to another is not always dramatic. Notwithstanding the fact that rounding errors might occur in the process, going from a "larger" workspace to a "smaller" workspace is really only an issue if the image converted contains colors that are out of the gamut of the destination workspace.
In other words, unless you have highly saturated colors that require the use of a larger workspace, converting to a smaller workspace won't do much harm.
Be careful, though. When you prepare images for the web, for example, and that you have to convert them from ProPhoto RGB 16-bit to sRGB 8-bit, you should always perform the profile conversion before you reduce the bit depth of the image, to reduce the harm in terms of rounding errors.
Needless to say, it is preferable to be working with a large workspace, using at least 16-bit color depth, and only performing such a conversion as the last step before exporting the final image.
10:30 am0
sRGB is not always worse than ProPhoto RGB
We often hear that ProPhoto RGB is a much larger working color space than sRGB and that, therefore, it is preferable to use ProPhoto RGB's larger workspace.
In a way, this makes sense. But first, we have to define what is meant by "larger". This is based on the fact that workspaces are usually represented in the form of graphs that overlap each other, like this:
Graph representation of common workspaces
Unfortunately, this is partly misleading. The fact of the matter is that the different workspaces all have the same quantity of possible colors, they just don't contain the same distribution of colors (extremes and/or tone curve).
In other words, if you have an 8-bit sRGB image (8-bit per channel, that is), it will be able to define colors using 256 tones per channel, whereas if you have an 8-bit ProPhoto RGB image, lo and behold, it will be able to define colors using 256 tones per channel as well!
...Wait, what?
The difference is that the actual color each workspace means by, say "255,0,0" is not the same. It will represent a more saturated red in ProPhoto RGB than it will in sRGB, because the extremes of the ProPhoto RGB workspace (i.e: its gamut) represent more saturated colors (as we can see in the graph).
For simplicity's sake, let's say the two workspaces define red something like this (this scale is totally arbitrary, but you get the idea):
Scales of red in two different workspaces
As you can see, both only have 256 tonalities of red available, but the ProPhoto RGB's maximum red is richer than the sRGB's maximum red. This is all very nice, but this also means that the difference between each of the tones of the ProPhoto RGB workspace is greater, because it has a longer scale to cover with just as many tones.
This is not good, because not every subject has reds that are that extreme — it varies depending on the contents of the image, and very often, out of gamut colors are indiscernible, conspicuous regions of the image.
Suppose we have a subject where no color extends beyond what can be represented in the sRGB workspace (which is not a rare occurrence). Say, for the sake of the argument, that the full scale of the sRGB workspace was exploited, but no more, leaving 256 tones to express color. Using the previous (arbitrary) scale, the same range of tonalities in ProPhoto RGB would fall between approximately 0 and 215 — this time leaving only 216 tones to express the same colors.
As you can see, in that case, using ProPhoto RGB would actually be detrimental to the overall quality of the image. It follows that for the utmost quality, ProPhoto RGB should really only be used when tonalities extend beyond the extremes of a "smaller" workspace such as sRGB.
Please note that this is squarely a technical discussion and that one should still use ProPhoto RGB as a working color space all the time. The distinction is just not worth the hassle — it would demand too much work to constantly have to check each image for colors that fall out of gamut. Moreover, since one should always work in 16-bit color mode (or more), the problem is mitigated to a point where it really doesn't matter.