Lightroom and every other program that I know of converts the RAW data captured by your camera sensor into actual pixels to work with. The RAW data can't even be viewed as an image, without converting to pixels. But regardless, Lightroom is entirely non-destructive, your original image in the RAW file is NEVER changed by Lightroom. So there is no reason to use layers in Photoshop to preserve the original RAW image; of course, there may be other reasons to use Layers in Photoshop in order to achieve edits that are not possible in Lightroom.
Back in the days when we weren't using Lightroom...just Photoshop...we opened a Raw file in Adobe Camera Raw. Although we looked at a jpeg version of the file in the window, all of the Camera Raw edits were made on the original electronic data. When we clicked "Open Image" and it opened in the Editor interface, pixels were assigned and from that point forward adjustments could be destructive.
I am curious about where Photoshop makes this conversion to pixels in Lightroom. The original Adobe Camera Raw adjustments are still in the Develop module so they should be operating as before. I'm assuming that Lightroom must assign pixels to this image at some point in the workflow.
all of the Camera Raw edits were made on the original electronic data
I'm not sure why you phrase it this way, but I would not phrase it this way. The electronic data is the RAW Image in the file, is it not? In order for ANY software to show you an image and then edit it, the image must be converted to pixels. The pixels are at no time "destroyed", as they can always be regenerated from the original RAW file.
But regardless of who's wording is more precise, Lightroom does the exact same thing as Camera RAW. In essence, Lightroom and Camera RAW are the exact same algorithms with a different user interface.
I am curious about where Photoshop makes this conversion to pixels in Lightroom.
I don't understand this. Lightroom and Photoshop are different software, Photoshop does not convert to pixels IN LIGHTROOM. Lightroom turns the RAW image into pixels whenever the original image needs to be rendered for viewing in the Develop module, or it turns the RAW image into pixels whenever the original image needs to be turned into a Preview in the Library Module.
You have some misconceptions there. The camera sensor is a pixel array. A raw file out of the camera is made of pixels.
The difference is that the raw file is grayscale data with linear tone response curve, because that's how the sensor records it. So it is just a very dark grayscale image.
The color is reconstructed in the raw converter, based on the color filter array in front of the sensor (known as a Bayer array). It also needs to be gamma encoded into an output color space, so that the tone curve corresponds to how the eye perceives the world. Very simplified.
There is no jpeg involved here, that's not what you're looking at. You're looking at the raw file, but processed according to the above.
Your response brings up this question. Where does the benefit lie in processing a Raw file versus a jpeg file in Adobe Camera Raw controls.
In experimenting a bit, I have compared the histograms within the editor, for the same image. The original file in Raw format is opened in Adobe Camera Raw. One version is simply moved into the Editor. without any changes. any looks the same as the original Raw image.
1. The original Raw file is processed to correct exposure in Adobe Camera Raw. That version is then opened in the Editor.
2. The jpeg version mentioned above is opened in Adobe Camera Raw and the identical changes made as for the Raw file. It is then opened in the Editor.
3. The jpeg mentioned above is opened directly in the editor with similar exposure corrections made via a Levels Adjustment Layer.
I will attach the histograms from these 3 cases. I see very little difference between 1 and 2 but considerable loss in image quality in the third instance.
I am not surprised by #3 but I expected richer histogram data in 1, then in 2.
After sending the detailed question, I realized that the variable I had overlooked was that jpeg images saved in the camera have been pre-processed by the camera software and so they don't have the full data that is in a Raw file. In my question, I used a jpeg created in Photoshop, not by the camera.
Does this explain why the jpeg I was using came through Adobe Camera Raw in good condition?
To process into a usable image, a large amount of sensor data have to be thrown away. Only a small subset is used. What you see on screen (or in print) is only this small subset.
The dynamic range in a good current sensor easily spans 12 stops or more. All this is recorded in the file. But no medium (screen or print) can reproduce that - you have perhaps half that at best, and the rest just has to be thrown out to maintain the tone response curve in the useful part. If you tried to cram it all in you'd end up with an extremely flat and dull image without any contrast or color. It just wouldn't look any good.
But all this information is still available in the raw file, if you want to go back and make re-adjustments. This is why, for instance, you can recover blown highlights from a raw file, but not from a jpeg.
The "combing" in the third histogram is typical of adjustments in 8 bit color depth, where you have 256 discrete values from 0 to 255. Jpeg only supports 8 bit depth. You only have 256 values to begin with, and any adjustments will bring them further apart.
I don't know if this will help. But Photoshop cannot edit raw image data. If you don't have Camera Raw installed you cannot do anything with your raw images in Photoshop. Camera Raw converts the image produced by the camera and displays pixel information. When you choose to open the image in Photoshop from Lightroom, Photoshop utilizes its Camera Raw plug-in to convert the image into pixel data. That pixel data is what is displayed in Photoshop. The data is no longer raw image data. It has been converted but hasn't been saved. When you are finished with your editing in Photoshop you are prompted to save the work. It has to be saved in a non-raw image format. The advantage of working in Lightroom or Camera Raw is that, although you are seeing pixel data, the underlying adjustments are being made to the raw data. And that is what gives you the extra flexibility when working in Camera Raw or Lightroom. Once the image is opened in Photoshop you have lost some of that flexibility. So that is why it is best to do as much of your editing in Lightroom or Camera Raw as possible.
I suspect this sounds like a lot of doubletalk. I have tried to explain it, but I hope I haven't just created more confusion.