On the left is an “Auto” Adjustment while the same data on the right is unadjusted. See below and you will discover that there is some serious misinformation on the web about ACR adjustments.
You may know that Photoshop does not know how to open raw files like NEF, CR2. Every time you open a raw file, it is actually opened by Adobe Camera RAW (ACR) which is an internal component common to Photoshop, Photoshop Elements and Lightroom. And there is an Adobe Camera Raw Defaults setting that is automatically applied per each camera type unless the user chooses custom settings. What you may not know is that I highly recommend stacking your star trail images without making any adjustments. Once you make adjustments, especially changes to contrast, tone curve, brightness, shadows or exposure you increase the visibility of gaps and noise. I explain why this is so in my “Down with the Noise Webinar“, but for now, just take my word for it!
Unfortunately it is quite complicated to remove the default Camera Raw adjustments due to conflicting details on web sites, including on Adobe’s own FAQ. As my experiments show, the “default” settings for ACR apply adjustments. Adobe says that using CTRL-R (CMD-R on a Mac) resets to the defaults for a RAW file, but it doesn’t reset everything because the default settings do have adjustments! Below are the choices for selecting, saving and resetting Camera Raw Defaults – you find this menu in the upper right of the ACR display – see more illustrations below.
In my tests with ACR 7.0 CTRL-R – which theoretically is the same operation as selecting Camera Raw Defaults - did not remove hand applied adjustments to clarity, tint, noise reduction, sharpening, vibration or saturation, tone curve, and other settings. What CTRL-R actually does is remove adjustments to Exposure, Contrast, Highlights, Shadows, Whites, and Blacks. Using the Camera Raw Defaults (first highlighted choice in the list above) doesn’t get what you might expect! So I went further. I set all the values to zero, then used Save Camera Raw Defaults, selected Camera Raw Defaults for the image and opened it using the Open Object button. When you use Open Object ACR creates a .XMP file – sometimes called a sidecar file – that I inspected to see what has been set. The non-zero settings in the XMP file after saving my custom camera raw defaults and choosing Camera Raw Defaults included the following non-zero settings:
When I saved my own Camera Raw Defaults I turned on Chromatic Aberration and Lens Profile correction and overrode the white balance to “Camera Faithful” just to be sure that the new Defaults were actually using my saved default settings. But wait! There are still Brightness and Contrast adjustments listed even though I had set those values to zero. It is also not clear whether it is applying a tone curve adjustment. The good news is that my saved defaults are NOT doing any sharpening or noise reduction whereas the ACR defaults (the default defaults?) do mess with those.
Before I tried to set my own Camera Raw Defaults, I followed advice I found online. That is how I discovered that the default, Default Camera Raw settings include both sharpening and color noise reduction.
Using the “Camera RAW Default” selection from the menu. Some changes are still being applied!
Notice how the settings file (XMP) contains adjustments for color noise reduction, a tone curve, and sharpening. The real head scratcher is that the side-car (XMP) file also shows adjustments to Shadows, Brightness and Contrast – which are NOT shown on the Basic (leftmost) settings panel for the image. Not knowing the internals of Photoshop, I can not tell if the brightness, shadow and contrast adjustments are actually present or not.
Basic does not show adjustments that are in the XMP file!
Unfortunately there are sites that claim that using the CTRL-U (CMD-U) sets all the values to default. This is incorrect. CTRL-U toggles between automatic and not automatic which is the clickable text Auto in the settings dialog. What I’ve called Default RAW Adjustments in my comparison photo at the top of this article is actually automatic adjustment – I was mislead! What is automatic? It is a roulette wheel whereby you let ACR take its best guess at what it thinks will look right. Apparently it is pretty smart unless you let ACR do its automatic thing on a night image in which case the result will not be very pleasing.
The stated Adobe method to reset to Camera Raw Defaults is to use CTRL-R (CMD-R on Mac). After using this magic sequence I see that there is still sharpening, a tone curve and much more.
Yeah, me too.
In fact, the default RAW setting can be per camera per ISO. The bottom line for me is that I do not trust ACR to not mess with my image unless I apply a Linear “Develop Settings” to all the images I’m going to load. And I am not even sure that some adjustments are not still being made despite my strong desire to have my images be unfooled around with.
But Why Do I Care?
A RAW file that has nether been sharpened nor had a tone curve applied looks flat and boringish. Why so boring? A digital camera records images in a linear fashion but our eyes don’t perceive things that way. To prevent people from squawking, ACR by default applies tonal adjustments to convert the raw data into something more adapted to what we see.
Of course you might ask why anyone would ever want to look at the un-adjusted image, and the answer is I wouldn’t want to either… but when stacking the fact that the pixels haven’t been diddled with beforehand makes the result better.
How do you get really RAW Raw Images?
For starters, you can set all of your Raw Defaults to Zero and save them as I noted in the Confusion Abounds section above. As a further belt-and-suspenders technique I also created a preset called “Linear” using the Save Settings menu. I apply the “Linear” preset to my images before I open them to force the sidecar files to be created. Whether ACR is still messing with some of the data is not clear.
But what about Cooked Images?
I don’t always go “really RAW” – I may tweak the settings in ACR for a more pleasing visual appeal. The literature indicates that ACR is a bit better at making adjustments than Photoshop is. The good news is that you can have your cake and eat it too because no matter what you do in ACR it does not change the data – just the adjustments that are applied to that data.
Here is how I made adjustments to the same image shown earlier along with all the non-zero values from the .XMP (sidecar file).
So if RAW is so Complicated I Should Stick to JPEGS, right?
Heavens no! If you shoot JPEGS rather than Raw you’re throwing away a lot of good data. The processing to convert the captured data into a JPEG involves lots of decisions made on your behalf, behind your back, and without the ability to change your mind later. Yes, you can diddle with the image, but you will not get the results you might if you had not let that little conversion monster distort your pristine data. In other words, you’ll eventually regret what happened.