# Image file directory (TIFF)

The image file directory for TIFF will contain a selection of the following entries:

* **File Byte Order:** OS defaults to the use of MM = Motorola Byte Order; the order in which the data is interpreted.
* **Tag 256 (ImageWidth):** The number of columns in the image, i.e. the number of pixels per row, for example, value = 4000.
* **Tag 257 (ImageLength):** The number of rows of pixels in the image, for example, value = 4000.
* **Tag 258 (BitsPerSample):** The number of bits per component, for example, value = 8.
* **Tag 259 (Compression):** Compression scheme used on the image data, for example, value = 5 (LZW).
* **Tag 262 (PhotometricInterpretation):** The colour space of the image data, for example, value = 3 (Palette).
* **Tag 270 (ImageDescription):** A string that describes the subject of the image, for example, value = 1:25 000 TILE SU41.
* **Tag 273 (StripOffsets)**: For each strip, the byte offset of that strip, for example, first four values = 5640 19678 35692 51409.
* **Tag 277 (SamplesPerPixel):** The number of components per pixel.
* **Tag 278 (RowsPerStrip):** The number of rows in each strip, for example, value = 8.
* **Tag 279 (StripByteCounts):** For each strip, the number of bytes in that strip after compression, for example, first four values = 14038 16014 15717 15442.
* **Tag 282 (XResolution):** The number of pixels per Resolution Unit in the Image Width, for example, value = 254.
* **Tag 283 (YResolution):** The number of pixels per Resolution Unit in the Image Length, for example, value = 254.
* **Tag 284 (PlanarConfiguration):** Look-up table, for example, value = first four values = 22873 31354 39321 59110.
* **Tag 296 (ResolutionUnit):** How the components of each pixel are stored. Default value is ‘2’ (inch).
* **Tag 306 (DateTime):** Date and time of image creation, for example, value = 2007:06:30 12:38:41.
* **Tag 317 (Predictor):** A mathematical operator that is applied to the image data before an encoding scheme is applied.
* **Tag 320 (ColourMap):** Look-up table, for example, value = first four values = 22873 31354 39321 59110.
* **Tag 339 (SampleFormat):** Specifies how to interpret each data sample in a pixel.
* **Tag 33432 (Copyright):** Copyright notice, for example, value = ORDNANCE SURVEY CROWN COPYRIGHT 2019.

{% hint style="info" %}
The preceding values are relevant to 1:25 000 scale TIFF data with LZW compression.
{% endhint %}


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