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How to open RAW images in GRIP

This technique is necessary if you have taken a photo in your camera's RAW mode and you want to view or process it with GRIP and you have not already used other software to convert it to a different format such as TIFF or JPEG.

  1. Open the image in GRIP by using the Open option on GRIP's main file menu. The image will be displayed in a separate window with its own menu bar. The image will probably appear to be completely black because it is only using the lower 4096 levels (12 bits) out of a possible 65536 (16 bits) for each channel.
    • You can prove that data are present without changing them: on the image's Measurement menu select "Whole image", to see the histogram of the image and statistics of the pixel data for each colour channel.
    • You can also look at the pixels to see what a RAW image is really like. To do this without altering the image go to the Measurement menu again but this time select "Hover and magnify". Then click anywhere on the image to get a highly magnified view in a new window, but still very dark. In this new window go to the Levels menu and select Auto-stretch. Either answer will do on the Yes/No dialogue after that. You will then see a brighter version of the magnified image, showing how each pixel in the RAW image has just one of the 3 primary colours because the detector chip has different coloured filters over each pixel.
  2. On the levels menu of the image window, select the "Interpret RAW" option. This interpolates between pixels so that every one gets a value for all 3 colour channels (red, green and blue). After interpolation the levels are stretched to cover 16 bits rather than 12 in each channel. The result appears in the same window, visible now but probably still seeming rather subdued.
  3. You may then want to use some or all of the following options from the levels menu to brighten it up.
    • Auto-stretch, which stretches contrast linearly so that the full (16-bit) range of levels is used.
    • Curves, which enables you to adjust contrast interactively by dragging a polygonal shape. This option also enables gamma curves to be set. The axes of the interactive graph cover the full (16-bit) range.
    • Saturation, which uses a slider. Moving the slider to the left desaturates colours in the image, eventually becoming monochrome (this is one way to convert an image to monochrome). Moving the slider to the right "removes grey" so that colours become more intense and ultimately, at any pixel, the lowest one of the channels (red, green or blue) becomes zero.
    • Colour balance. This uses 3 sliders to adjust the relative amounts of red, green and blue at all pixels in the image.
    • Convert to 8 bits per channel, particularly before saving the image as JPEG if that is your requirement.
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