Why does Rawstudio show 0–255 RGB values for a RAW image?
Asked 4/1/2013
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When I open RAW files from my Canon 600D/T3i in Rawstudio and move the mouse over the image, the RGB readout shows 8-bit values from 0 to 255. Since the source file is RAW, I expected higher-bit sensor values instead.
Why does the software display 8-bit RGB numbers, and how are the original RAW values actually stored and distributed by channel?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
2 Answers
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You're not looking at the "raw" values, you're looking at the "developed" values, given the current settings, in an 8-bit-per-channel colour space. And that's the case with most image software — when you're working in an RGB colour space, the values you use are 8-bit values, even if the image you are currently working with is in a 16-bit, 32-bit or arbitrary-depth colour mode. The higher bit depth is used behind the scenes for computation, but the image you are actually working with in the UI is an 8-bit image.
Knowing the actual value wouldn't help a whole lot either, since it only has meaning when you also know the min and max values. The same camera may be capable of recording at different bit depths under different circumstances, so what (7567, 8993, 2214) means is a moving target. (59, 70, 17) in an 8-bit space, is always olive drab no matter what the underlying image depth might be.
Originally by user2719. Source · Licensed CC BY-SA 4.0
user2719
13y ago
0
Generated from our catalog & community — verify before relying on it.
The 0–255 numbers are almost certainly not the camera’s original sensor values. They’re the displayed or “developed” RGB values after the RAW data has been converted into a normal RGB image for preview and editing.
That’s common in RAW software: the program may process internally at higher precision, but the on-screen readout is often shown in an 8-bit-per-channel RGB space for the UI.
RAW data itself is not simply an 8-bit RGB image. A RAW file stores sensor measurements before full RGB conversion, and the meaningful numeric range depends on the camera and capture settings. So a raw value only makes sense if you also know the black level, white level, and bit depth used by that camera/file.
In short:
- 0–255 = preview/developed RGB readout
- not the original RAW sensor data
- RAW values are higher precision and camera-dependent
- the software may still use higher precision internally even if the UI shows 8-bit values
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