Opening Raw Documents

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A raw document is a plain binary file stripped of all extraneous information. It contains no compression scheme, specifies no bit depth or image size, and offers no color mode.

Each byte of data indicates a brightness value on a single color channel, and that’s it. Photoshop offers this function specifically so you can open images created in undocumented formats, such as those created on mainframe computers.

To open an image of unknown origin, choose File>Open As. Then select the desired image from the scrolling list and choose Raw (*.raw) from the Open As pop-up menu. After you press Enter, the dialog box appears, featuring these options:

  • Width, Height: If you know the dimensions of the image in pixels, enter the values in these option boxes.
  • Swap: Click this button to swap the Width value with the Height value.
  • Count: Enter the number of color channels in this option box. If the document is an RGB image, enter 3; if it is a CMYK image, enter 4.
  • Interleaved: Select this value if the color values are stored sequentially by pixels. In an RGB image, the first byte represents the red value for the first pixel, the second byte represents the green value for that pixel, the third the blue value, and so on.

If you turn this check box off, the first byte represents the red value for the first pixel, the second value represents the red value for the second pixel, and so on. When Photoshop finishes describing the red channel, it describes the green channel and then the blue channel.

  • Depth: Select the number of bits per color channel. Most images contain 8 bits per channel, but scientific scans from mainframe computers may contain 16.
  • Byte Order: If you specify 16 bits per channel, you must tell Photoshop whether the image comes from a Mac or a PC.

  • Header: This value tells Photoshop how many bytes of data at the beginning of the file comprise header information it can ignore.

  • Retain When Saving: If the Header value is greater than zero, you can instruct Photoshop to retain this data when you save the image in a different format.

  • Guess: If you know the Width and Height values, but you don’t know the number of bytes in the header—or vice versa—you can ask Photoshop for help. Fill in either the Dimensions or Header information and then click the Guess button to ask Photoshop to take a stab at the unknown value.

Photoshop estimates all this information when the Raw Options dialog box first appears. Generally speaking, if it doesn’t estimate correctly the first time around, you’re on your own.

But hey, the Guess button is worth a shot. If a raw document is a CMYK image, it opens as an RGB image with an extra masking channel. To display the image correctly, choose Image>Mode>Multichannel to free the four channels from their incorrect relationship. Then recombine them by choosing Image>Mode>CMYK Color.

Saving A Raw Document With Photoshop

Photoshop also enables you to save to the raw document format. This capability is useful when you create files you want to transfer to mainframe systems or output to devices that don’t support other formats, such as the Kodak XL7700.

Do not save 256-color indexed images to the raw format or you will lose the color lookup table and, therefore, lose all color information. Be sure to convert such images first to RGB or one of the other full-color modes before saving.

When you save an image in the raw document format, Photoshop presents the dialog box. The dialog box options work as follows:

  • File Type: This option is a carry-over from the Macintosh, where it defines information for the resource fork. In Windows, the option is always dimmed. Feel free to ignore.
  • File Creator: Ditto. The default code 8BIM is selected for you and the option is dimmed.

  • Header: Enter the size of the header in bytes. If you enter any value but zero, you must fill in the header using a data editor such as Norton Disk Editor.

  • Save Channels In: Select the Interleaved Order option to arrange data sequentially by pixels, as described earlier. To group data by color channel, select Non-interleaved Order.

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