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I have two images one is an HDR image created by the Devebec algorithm, and the other is a low dynamic range image, then how can we calculate the actual bit-depth of the images? Both are supposed to have different bit-depth levels since the dynamic range is different. How can we calculate it?

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  • \$\begingroup\$ Your question does not make a lot of sense if interpreted literally. Define "actual". \$\endgroup\$
    – Euri Pinhollow
    Commented Mar 18 at 8:41

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I never heard of this algorithm but judging by information I found it's a tone mapping algorithm. Tone mapping does not change the bit depth of output. Tone mapping is essentially modifying too bright regions of the image to be of similar brightness as the rest of the image (even though specifics may vary and shadows and highlights can be treated differently).

Both are supposed to have different bit-depth levels since the dynamic range is different.

I do not know what's the foundation for this assumption. Typically a true HDR image (the one which has brightness metadata and thus should be displayed on an HDR display) is expected to have high bit depth to prevent banding but is not obliged to.

There is no such rule about tone mapping.

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If the image is a jpeg or a color png it is 8bit. A png can be 16bit, but that's uncommon. For it to be in 16bit + alpha floating point (32 bit) it must be in a format that allows for that... psd/tiff/xcf/etc, and opened in a program that can work with 32bit color (adobe/gimp/etc).

Many programs will show you what a 32 bit image looks like by showing you the embedded 8bit jpeg... e.g. file browsers. And many of those programs will also tell you what the color bit depth of the file is recorded in the metadata.

This is a 32bit tiff shown in Adobe Bridge (it is displaying the 8bit embedded file/thumbnail).

enter image description here

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  • \$\begingroup\$ PNG support 16-bit/channel color, but that's 16-bit integer, not floating point even for the alpha channel. \$\endgroup\$
    – xenoid
    Commented Mar 18 at 21:41
  • \$\begingroup\$ @xenoid, corrected... \$\endgroup\$
    – Steven Kersting
    Commented Mar 18 at 23:31

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