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Convert from 32 bits to 8 or 16 bpc

HDR images contain luminance levels that far exceed the luminance data that can be stored in 8‑ or 16‑bpc image files. You can make exposure and contrast corrections when converting a 32‑bpc HDR image to 8 or 16 bpc to produce an image with the dynamic range (tonal range) you want.

  1. Open a 32‑bpc image and choose Image > Mode > 16 Bits/Channel or 8 Bits/Channel.
  2. In the HDR Conversion dialog box, choose a method for adjusting the brightness and contrast in the image:
    Exposure and Gamma
    Lets you manually adjust the brightness and contrast of the HDR image.

    Highlight Compression
    Compresses the highlight values in the HDR image so they fall within the luminance values range of the 8‑ or 16‑bpc image file. No further adjustments are necessary; this method is automatic. Click OK to convert the 32‑bpc image.

    Equalize Histogram
    Compresses the dynamic range of the HDR image while trying to preserve some contrast. No further adjustments are necessary; this method is automatic. Click OK to convert the 32‑bpc image.

    Local Adaptation
    Adjusts the tonality in the HDR image by calculating the amount of correction necessary for local brightness regions throughout the image.

  3. (Optional) Click the arrow to display the toning curve and histogram. The histogram shows the luminance values in the original HDR image. The red tick marks along the horizontal axis are in 1 EV (approximately 1 f‑stop) increments. The toning curve is active only for the Local Adaptation method.
  4. Do any of the following:

    • If you chose Exposure and Gamma, move the Exposure slider to adjust the gain and move the Gamma slider to adjust the contrast.

    • If you chose Local Adaptation, move the Radius slider to specify the size of the local brightness regions. Move the Threshold slider to specify how far apart two pixels’ tonal values must be before they’re no longer part of the same brightness region. You can also use the Toning Curve and Histogram to make adjustments.
      Note: The Toning Curve and Histogram usually lets you make limited changes from point to point and attempts to equalize your changes across the points. If you select the Corner option after inserting a point on the curve, the limit is removed and no equalization is performed when you insert and move a second point. You’ll notice that the curve becomes angular at a point with the Corner option applied.
      Toning Curve and Histogram adjustment using the Corner option

      A.
      Inserting a point displays the Corner option.

      B.
      Adjusting new point makes the curve angular at the point where the Corner option is used.

  5. (Optional) To save your 32‑bit toning options as a file, click Save. Type a name for the file in the Save dialog box and click Save.

    You can reuse the saved 32‑bit toning option file. Click Load to convert another 32‑bpc image to an 8‑ or 16‑bpc image.

  6. Click OK to convert the 32‑bpc image.