6 Replies Latest reply on Oct 18, 2010 10:58 AM by web.boards

# How many bits are raw images?

1. How many bits are images taken from a camera with a proprietary format? Are they 12 bit or 16?

2. After making adjustments in ACR, do you bring the image into Photoshop at 12 or 16 bits?

Thanks.

• ###### 1. Re: How many bits are raw images?

Raw captures are 12, 14 or 16 bits (depends on the camera) and are opened into 8 or 16 bit precision based on the Camera Raw preferences.

• ###### 2. Re: How many bits are raw images?

1.How many bits does the average point-and-shoot camera capture when shooting jpgs?

2. How much of a visible difference is there between 12, 14, and 16 bit raw files?

3. What do you mean by the are "opened into 8 or 16 bit precision based on the Camera Raw preferences"? Does this mean that some of the bits could be thrown away if they are opened with 8 and it was taken with 16 bits?

Thank you.

• ###### 3. Re: How many bits are raw images?

Older Canon compact cameras capture images in 10 bit precision, while new one in 12 bit. Most DSLR raw-s are 12 or 14 bit, some 16 bit. Those raw data are linear (with some exceptions, like some Nikon cameras, where linear data from sensor are/can be stored as nonlinear in raw file), while output files (jpg, tiff) in sRGB/Adobe  RGB,/ Photo Pro / whatever are usually nonlinear, encoded with some  gamma function.

When converting from linear input color space to nonlinear output color space, bits are not thrown away - color is converted from one color space to another and result is finally rounded to 8 / 16 bit

More bits in raw brings theoretically some improvement, but mostly in  shadows, because of difference linear vs. nonlinear

• ###### 4. Re: How many bits are raw images?

web.boards wrote:

1.How many bits does the average point-and-shoot camera capture when shooting jpgs?

2. How much of a visible difference is there between 12, 14, and 16 bit raw files?

3. What do you mean by the are "opened into 8 or 16 bit precision based on the Camera Raw preferences"? Does this mean that some of the bits could be thrown away if they are opened with 8 and it was taken with 16 bits?

Thank you.

Jeff Schewe has answered the question about bit depth of the raw capture, but one must realize that noise in the image limits the effective bit depth of the capture, since it does not make sense to quantify the signal from the sensor in steps finer than the level of noise in the image. These considerations are discussed in an excellent article by Emil Martinec:

http://theory.uchicago.edu/~ejm/pix/20d/tests/noise/noise-p3.html#bitdepth

Some of the newer high end dSLRs offer 14 bit quantization, but the gain in levels is often negligible because of noise. P & S cameras are much noisier than high end dSLRs and their effective bit depth in terms of the number of actual levels that can be perceived in the rendered image is open to question. There is a loss of levels when one goes from a linear raw space to a gamma encoded space such as Adobe RGB. Bruce Lindbloom's levels calculator can calculate this loss. The reader should try a few values with the calculator using the bit depth of the camera and a gamma of one and a gamma of 2.2 for the aRGB. With Photoshop, use a bit depth of 8 or 15, since Adobe uses a bit depth of 8 or 15 in Photoshop, effectively halving the number of levels over what could be obtained with full 16 bit output. However, for current cameras, this is of no significance.

http://www.brucelindbloom.com/

• ###### 5. Re: How many bits are raw images?

> 3. What do you mean by the are "opened into 8 or 16 bit

> precision based on the Camera Raw preferences"? Does this
> mean that some of the bits could be thrown away if they
> are opened with 8 and it was taken with 16 bits?

You can choose in ACR how many bits to retain when you generate the output file.

That is, you use ACR to read in an image, process it, and produce an output file. That output file is usually a TIFF or JPEG (or opened directly into Photoshop).

How many bits do you want that file to be? That is what Jeff refers to in this choice (8 bits versus 16 bits). Note that if you choose to save a JPEG then the result will be 8 bits (i.e., there is no 16-bit JPEG).
• ###### 6. Re: How many bits are raw images?

I was always under the impression that the number of bits described how many colors could be included in the file, and I thought you would want the highest bit file possible for later editing. How many bits will a .psd store? Wouldn't you want to just save a .psd and edit the file further in Photoshop?