Supported file formats

Out-of-camera RAW files and DNG files

FastRawViewer supports RAW files from practically all consumer digital cameras. For a complete list of supported cameras, please see the List of Supported Cameras section at the end of this manual.

Furthermore, all versions of DNG files that comply with DNG 1.4 specifications are supported, including those recorded not by just cameras but also by video cameras (CinemaDNG, if a standard compression method is used), mobile phones, and various applications (panorama stitching software, programs for work with HDR compositing, etc.).

Previews are supported for RAW files (in “Grid Mode” or in the Filmstrip) that include JPEGs or bitmap previews in the RAW file. Such previews are commonly present in RAW files recorded by digital cameras, but they may be absent in CinemaDNG files, photos taken by phones, or DNG files that were recorded by some third-party applications. If there is no embedded preview in the RAW file, then instead of the preview, you will see an icon that says No preview available.

For RAW files, non-destructive, parametric editing is supported: the rendering parameters (such as white balance, exposure correction, contrast) are recorded to XMP files and will be applied automatically the next time that the file is opened with FastRawViewer or one of the Adobe RAW converters.

JPEG files

FastRawViewer supports the following types of JPEG files: 8-bit, both RGB and monochrome.

PNG files

FastRawViewer supports 8/16 bit PNG files, both RGB and monochrome. Transparency and background color are not fully supported.

For PNG files, EXIF display is guaranteed only in Single File View Mode.

TIFF files

The following formats are supported:

  • TIFF and BigTIFF (EXIF display is supported only for standard TIFF files)
  • RGB and Grayscale:  8/16 bit integer, 16/24/32 bit floating point
  • LAB: 8/16 bit integer.
  • CMYK: by default, any support for this format is turned off. One can turn it on, but only a grayscale conversion will be displayed (See the section on “Additional Settings”).

The default file extensions for TIFF files are: .TIF and .TIFF. If one needs to process TIFF files with a different extension (for example, .fff for Imacon/Hasselblad scanners), this can be enabled through the the AdditionalTIFFExts script (See the section on “Additional Settings”).


Support for HEIC/HEIF file formats is implemented only in:

  • Windows 64-bit version, for Windows (Windows 7 – Windows 10)
  • macOS versions for current versions of macOS (10.12-10.16/11.0)

The following HEIC/HEIF file variants are supported:

  • The file type (in the header) is heic or heix

    Other format variations (msf1, mif1, mif2) are not supported.
  • 8 and 10 bits
  • Color data support:
    • Embedded ICC profile (files originating in Apple devices)
    • Files from Canon cameras are recognized by the metadata, and ITUR_2100_PQ_FULL  profile is assigned
    • For other metadata variants (RGB Primaries/Transfer curves), the sRGB color space will be assigned

The H.265 decoder embedded in FastRawViewer is launched only if the program is displaying HEIC/HEIF files.

Determining the file type

FastRawViewer determines the file type based on the file extension:

  • .JPG, .JPEG – JPEG file formats
  • PNG – PNG file formats
  • .TIF, .TIFF – TIFF file formats

    (because some older cameras used to record RAW files with the .TIF extension, before opening a .TIF file, FastRawViewer checks if that’s actually a RAW file; if it is, it opens it as such).
  • HEIC/HEIF format: the extensions are indicated in Preferences – File Formats – HEIC/HEIF files support – HEIC/HEIF files extensions (types). Default list: *.HEIC *.HEIF *.HIF
  • All other file extensions known to FastRawViewer are treated as RAW files.

Files extensions that are unknown to FastRawViewer are not displayed in the list of files (Menu – File – Open, the list of files in the current folder).

If your RAW files have extensions not supported in FastRawViewer by default, you can list additional extensions through Preferences – File Handling – Additional RAW extensions.

If some files on your computer are not actually RAW files, but FastRawViewer is displaying them in the list of files, you can explicitly exclude the corresponding extensions through Preferences – File Handling – Ignore Extensions when file browsing.

Maximum file sizes

Because file sizes (both in megapixels and megabytes) can be very large, while FastRawViewer performs all of its actions on them in the RAM, the program allows one to set limits on these through Preferences – Performance – File Size limits:

  • Downscale JPEGs larger than .. Mpix: if the JPEG file is larger than the limit set, the file will be downsized so as to not exceed the stated limit.
  • RAW files size limit: .. Mpix: if the size of the RAW file is larger than this limit, the RAW data will not be unpacked, and only the preview (if it exists) will be displayed.
  • TIFF files size limit, PNG files size limit: if the size of the TIFF file exceeds the limit, it will not be displayed in Single File View Mode.
  • TIFF thumbnail generation limit/PNG thumbnail generation limit: for files larger than this limit, previews will not be displayed.

The default limits are set based on the following considerations:

  • 32-bit version: FastRawViewer has access to 2 GB of RAM (this is the natural limit for 32-bit applications).
  • 64-bit version: the assumption is that 4-6 GB of RAM are available.

If you are using the 64-bit version, and you have additional RAM installed on your computer, you can increase the default limits. Please take into account the following:

    • The number of files stored in RAM is set through Preferences – Performance – JPEG/PNG/TIFF cache size.
    • Each megapixel requires 4 MB of RAM
  • RAW files
    • The number of files stored in RAM is set through Preferences – Performance – Decoded RAW cache size
    • Each megapixel in a RAW file requires from 2 (Bayer and monochrome) to 8 (Linear DNG, 4-shot) MB of RAM.
    • For processing, the programs uses from 6 (Bayer and monochrome) to 24 MB per megapixel.


With default settings, FastRawViewer combines RAW and JPEG files with the same name.

For this operation, the extension of the JPEG file must be .JPG or .jpg.

In cases where one folder has several RAW files with the same name (but different extensions), the JPEG will be combined with the RAW file, the extension of which is alphabetically earliest.

One can switch off RAW+JPG combining by turning off the setting Preferences – File Types – Handle RAW+JPEG together.



It works similarly to RAW+JPEG mode. RAW+HEIC mode is intended for use with Canon cameras that are set to HDR mode (in HDR mode, the camera will record HEIF files instead of JPEGs).

This mode is turned on by simultaneously switching on the following settings in Preferences – File Formats:

  • Join RAW+JPEG
  • HEIC/HEIF file support
  • Joint RAW+HEIC

If the current folder has a RAW file, a JPEG file, and a HEIC file (all with the same filename), then the RAW and JPEG will be joined.

Preview and Metadata cache

FastRawViewer stores metadata (EXIF, XMP) and previews for files that have already been browsed in the RAM. The RAM size for these caching operations is set through Preferences – Thumbnail cache:

  • Thumbnail cache size – how much is set aside for previews (in MB)
  • Metadata cache size – how much is set aside for metadata (in # of files; the metadata for one file takes up just a few KB)

Disk cache for previews

Because TIFF and PNG files can be of any size and lacking in embedded previews, FastRawViewer version 1.5 implements preview storage using a special database file on the disk (the file is in the SQLite format).

Only previews for the files where the preview generation takes more time than is set through Preferences – Thumbnail cache – Save cached thumbnail if image thumbnail extraction was longer than… msec will be stored in this file. This allows for two things: first, there will be no rebuilding of previews that take a long time to create. Second, the database of previews won’t grow uncontrollably fast.

The path to the file is set through Preferences – Thumbnail cache – Thumbnail database path. Defaults are:

  • Mac: ~/Library/Application Support/libraw-llc/FastRawViewer
  • Windows: $HOME/AppData/Local/LibRaw LLC/FastRawiewer

We strongly recommend that you select a fast (SSD) drive to store the preview database (if such is available in your system).

When the parameters are set to default, the size of the previews stored in the database is the larger of the preview sizes set for the Grid and the Filmstrip. If you increase the size of the displayed previews, then FastRawViewer will offer to purge the saved preview database. Alternatively, the size of the previews being saved can be set through Preferences – Thumbnail Cache – Stored thumbnail size to be Maximum thumbnail size. In this case, no preview database purge is necessary when changing the size of the previews, but the database itself will take up more space.

Other database parameters are described in the section on “Program settings” section, under Performance – Thumbnail cache.

One can use the following menu elements to control the preview database:

  • Menu – File – Reload – Clear Thumbnail database – purge all thumbnails from the database.
  • Menu – File – Reload – Fetch thumbnails for current folder – build all of the previews for the current folder, and save those that took more time than the is set through Preferences – Thumbnail cache – Save cached thumbnail if image thumbnail extraction was longer than… msec.