The hopper wrote:
I currently use Lightroom (OK, not too well) and am trying to learn Photoshop. My understanding is that if you do work in Photoshop on a RAW file, you permanently change the file. Firstly, is this correct? and second, does this mean you should create a copy of the original and work on the copy so you don't "corrupt" the original??
2) No, because original raw files are NOT EDITABLE. By definition, the data is what came off the sensor. It is permanently locked as what it is. You can change the formula for the OUTPUT from that data, but then to view or use that conversion, the raw data must be de-mosaiced and decoded and processed by software. That is what happens when you OPEN the file in ACR (Adobe Camera Raw, which is the Develop module in Lightroom Classic or the ACR filter in Photoshop.)
3) You should always have a backup of your files, in case a drive becomes corrupted or there's a fire or flood or other disaster.
When editing in Lightroom Classic, you are saving ONLY data *about* your original data, plus a small proxy of that converted, edited data. The original file, regardless of file type, is left intact. When you export, print, display as a slide show, paginate as a book, or upload to the web, you are getting a COPY of the original file, WITH CHANGES APPLIED.
In Photoshop, you WILL change any other kind of file other than raw when you save it on top of itself. Raw files are "Save As..." (a different file type) only.
The very conversion of raw camera data to any other file type limits it to the parameters of that conversion. This is why Photoshop offers different bit depths and wide gamut color spaces. It helps you preserve as much of the original data as possible, during the conversion. Raw file
— What the camera recorded, with minimal processing (Raw files include a JPEG preview processed with the menu settings of the camera.).PSD and 16-Bit TIFF, in ProPhoto RGB color space
— very reasonable conversion choices when working from raw files in Photoshop16-bit TIFF in Adobe RGB
— requested by SOME professional publishers, offset printers, boutique (high end) gicleé printers so they can adjust your files to look best on their equipment, with the least amount of damage8-bit JPEG in sRGB
— used by most professional color labs using silver halide photo paper (Kodak or Fujifilm papers exposed on laser or LED printers and processed in RA-4 or equivalent chemistry) PLUS, used by most of the entire Internet world, on office monitors, by most amateurs, etc.
JPEGs made in the camera "can" be adjusted with post-processing software. However, the best "JPEG capture" workflows rely on controlled lighting, extremely accurate exposure and white balance techniques, and careful setting of the camera menu controls for the JPEG processor. That way, little or no adjustment is required. Set the camera to use the largest possible JPEG pixel dimensions with the highest possible quality/least compression/largest file size. When post processing, use Lightroom Classic so only ONE JPEG save is performed — on export, print, post, paginate, or display.
To "corrupt" a file means to damage a file in such a way that it either cannot be opened, or the contents of the file are partly unusable. Opening and saving a JPEG on top of itself does not corrupt it. It MAY throw away enough data to show noticeable quality loss (jaggies, flat color, ridging in gradient areas, mosquito noise, and other artifacts). That is file degradation, not corruption.
In the pro lab world I used to work in, we set rules that:
> We always worked on COPIES of customer data.
> We would never open and save a JPEG file on top of itself more than twice (and only once in most cases). Save #1 was a color/brightness correction. Save #2 was after portrait retouching or other work in Photoshop.
> We would always save the largest JPEG with the least compression.
This discipline worked fine. When we needed more malleable files, we converted 8-bit JPEG in sRGB to 16-bit .PSD or TIFF in ProPhoto RGB, did our complex edits, then saved back to 12-quality or "100"-quality JPEG at 8-bits and sRGB color. This preserved maximum quality with maximum flexibility for multiple saves during adjustments.
I know that is more than you asked for, but hope that it broadens your understanding of why you have the options you do.