About RawToPpm16

Aug. 1999

Tomoo Mitsunaga

(1) Function

RawToPpm16 is an image converter, which convert a RAW format image to a PPM16 format image.

(2) When is RawToPpm16 used

RASCAL currently supports only PPM16 format as 16bit image format. You may want to make a PPM16 format image for experiments with RASCAL. However, since PPM16 format is specially made for RASCAL, there is no common tool to make a PPM16 format image. So, we provide RawToPpm16 as one of tool to make a PPM16 format image.

# To display a PPM16 image, you can use radianceView in RASCAL. Or, you can load a PPM16 image as a RAW image with Adobe Photoshop. You can also use XV, which is one of famous image viewers on UNIX, to display a PPM16 image.

# To convert a PPM16 image to other format image, you can use Adobe Photoshop. Photoshop currently supports Photoshop format and TIFF format for 16 bit images.

(3) About RAW format

RAW format is used in Adobe Photoshop to treat an arbitrary raw bit array as an image data. You can save a 16bit image, which can be captured or scanned through a TWAIN driver with an over-8bit imaging device such as digital cameras or scanners, with RAW format. Once you have saved a 16bit RAW image, you can convert the RAW image into a PPM16 image by using RawToPpm16.

Several options must be specified when you save a RAW image. To make a PPM16 image, you have to save a RAW image with the following options.

Header : 0
Save Channels In : Interleaved Order
Byte Order : IBM PC

You also have to make sure that the "image mode" of the image is "16bits / channel".

Note that you have to remember the width and height of the image because RAW format does not contain the information of the dimension of the image. But inputting the dimension is required when RawToPpm16 converts the RAW image.

(4) About PPM16 format

PPM16 format is a specially made image format for RASCAL. Since PPM16 format is a simple extension of PPM format, which is one of very commonly used image formats, it is very easy to understand and use. The difference between PPM and PPM16 is only data length (8bit for PPM and 16bit for PPM16). As PPM format has, PPM16 format has a very simple header, which includes the information of width, height and maximum value, followed by RGB data with top-left origin and interleaved order.

As a PPM image can be read as a 8bit RAW image by Photoshop, a PPM16 image can also be read as a 16bit RAW image by Photoshop. When you load a PPM16 image with Photoshop, use options showed as followings.

Channels

Count : 3
Interleaved : checked
Depth : 16bits
Byte Order : IBM PC

Header

Size : (Use "Guess" button to let Photoshop estimate the header size.)

You also have to specify the width and height of the image.

(5) How to use RawToPpm16

Double click RawToPpm16.exe.
Type <an input image file name> after "inimage …"
Type <width of the input image> after "width …"
Type <height of the input image> after "height …"
Type <an output image file name> after "outimage …"
Program starts to convert the image. … End.