F4W2HDU Guide Start at the Top Download Install

FITS4Win2 Header Data Utility

A FITS Utility
  • Bulk load, view, search and update headers
  • Search headers by keyword or property name
  • Keyword value edit and save to update plan
  • Update plan review and edit
  • Update plan processing to files
  • Built-in Windows 7-style file Explorer
FITS4Win2 Config
  • Update automation
  • Trial period tracking
  • Registration control
  • Installed components
  • Support links
FITS4Win2 Header Data Utility Interface

The FITS4Win2 Header Data Utility is available for free download and use by the FITS user community. As well as being a bulk header editor, F4W2HDU allows quick display of raw headers, translating between property names and keywords, with synonymous keyword detection and a keyword library compiled from several sources, including the FITS Standard (NASA), NOAO, ESO and SBIG public keyword libraries.

F4W2HDU Installer Download

If you are currently And Then
A FITS4Win2 Trial UserYour Trial is still active Do not install this F4W2HDU
The version installed with the Trial is needed for Trial Status reporting.
An Expired Trial User You do not want to register FITS4Win2 but
You do want to keep using F4W2HDU.
Uninstall the FITS4Win2 Trial and install F4W2HDU from below.
Using a F4W2HDU StandAlone Version Your installed version is less than 1.3.0 Download and Install the F4W2HDU StandAlone from below to update your current version.
Anyone else You want to try F4W2HDU You are welcome to Download and Install the F4W2HDU Stand Alone from below. F4W2HDU is Free for unrestricted use.

v3.6.5 64-Bit for Windows 10 and higher
Size: ~10MB Released: 24-Jun-2023
If the download doesn't work right-click and select download link. You may also need to let your browser 'keep' the download from the task bar.

v3.0.0 32/64-Bit for earlier than Windows 10
Size: ~10MB Released: 22-Aug-2022

Minimum System Requirement Any 32 or 64-bit, Windows Vista, Windows 7, 8, 10 or 11

Run the Standalone Installer

Right click the downloaded installer file and select 'Run as administrator'
Install as Administrator

On the installation start screen- click "Next".
Setup Screen

If the security warning appears - Click "Run"
Click Run on Security Warning

If the User Access Control screen appears - select "Allow" to continue.
Allow User Access Control

Install Complete When the installation is complete you can check the "Launch" box to run F4W2HDU or just press "Finish". A shortcut to F4W2HDU can be found on both the "Desktop" and in "Start Programs".

The 'FITS Header Tool' Overview

Load, View, Search and Update headers.

F4W2HDU Interface

The FITS Header Tool screen. All functionality is arranged onto the four Tabs near the bottom
'Header Entries' , 'Update Plan' , 'Process Files' and 'File Explorer'

Loading FITS Files

File Handling

Files can be loaded into F4W2HDU three ways:

  1. Image files can be 'Drag and Dropped' into the file list from anywhere in Windows, including F4W2HDU's built-in File Explorer
  2. Selecting "Open with" and F4W2HDU" from a right-click context menu as shown below. FITS file context menu for loading into F4W2HDU
    Note that multiple FITS files can be selected for load, however if any of the selected files are not FITS files, 'F4W2HDU' will not appear in the context menu, though the files can all be drag and dropped into the file list. In this case only the FITS files will be loaded.
  3. Pressing the Load Files button (left) will provide a standard windows file open dialog box, which itself is as configurable as windows explorer.
LoadedCounter Number of files loaded
Load Button Load files
Collect Checkbox When loading files, add to the list. When unchecked, loaded files will replace those loaded at the time.
This setting applies to all load methods
SelectedCounter Deselect (uncheck) all files
None Button Deselect (uncheck) all files
FlipButtonInvert the selection of all files
AllButton Select (check) all files
RemoveButtonUnload selected (checked) files

Multiple files can be loaded simultaneously however any FITS file in a specific folder, can be loaded only once. Attempting to load the same file more than once will fail. Loading a batch of files where one or more are already loaded, will fail for the existing files, but succeed for the rest. Multiple files with the same filename and in different folders, can be loaded simultaneously.

Header Entries Tab

Selecting a file from the loaded file list will display it's header in the Header Entries Tab. Headers are displayed in the order that they were read and displayed as they exist in the file. Header records are placed into the editor whenever a keyword is selected.

Headers The Header View shows the raw header record. Keyword, Assignment Value and Comment.

These conform to the FITS specification character lengths for each 80-byte header record:

FieldChar Length
Keyword 8
ColumnPossible ValuesDescription
? Tick or Cross A Tick means the value can be edited, whereas a Cross indicates a read-only value
Keyword Any FITS keyword As read from the file
Value The value for this keyword As read from the file. Non-string values are limited to 20 characters in columns 11-30
Comment A textual comment As read from the file. Note that string Values may take up the entire Value+Comment length of 70-characters, whereas non-string values can have an independently editable 50-character comment string in columns 31-80.

Searching for Keywords

Keyword searching is simply a matter of selecting a record from the displayed header or selecting an image property name or keyword from either of the selection lists. Details of the selected keyword are displayed in a tooltip by hovering the mouse cursor over the Keyword Library list. Search results are shown as symbols to the left of each selection list, described further below.

Keyword Selection Lists

Keyword and Property selection lists

Selecting an entry from the Keyword Library (left) or Image Property (right) lists as shown here, will display an exact or synonymous match in the other list as well as the displayed header (below). Both lists are in alphabetical order.

Pressing the first letter of a desired keyword will scroll the list to the first entry with that letter.

  • Keyword Library - is for General Use and lists the complete F4W2HDU Keyword library comprising 130+ keyword definitions from various sources including the FITS standard, HEASARC, NOAO and SBIG keyword dictionaries.

  • Property Name - Lists all Windows Image Properties currently provided by FITS4Win2. Each Property name maps directly to one base keyword in the Keyword library and 0 or more synonymous keywords .

Keyword Search Results

When a keyword is selected either from the header, Keyword or Property selection lists, the search results are indicated by an equivalence symbol at left of each list. Left of the Keyword list, the symbol represents the relationship between the listed library Keyword and the displayed Header. At left of the Property box indicates the relationship between the listed Property and the listed library Keyword.

Keyword match in Header
Indicates matches between Header and Keyword Library
Property matches Keyword
Indicates matches between Keyword Library and an Image Property
equals Match Found. Match found.
Not Equals No Match. No Match.
Is Synonymous Keyword Synonym Match. Synonym Match.
The direction of the match is determined by whatever was selected and can be seen by hovering the mouse cursor over the equivalence symbol. Read more about synonymous keywords below.

Header Keyword Search

When a Header Record is clicked, the two selection lists are searched for a match and synchronised to the header keyword. If the keyword is not found, it is considered of unknown type, but can still be edited as a string.

Synonymous Keywords

Some keywords have been duplicated and represent data for which a keyword already exists. For example, EXPTIME, EXP-TIME and EXPOSURE are all commonly used to represent the exposure time in seconds. Similarly APTDIA and APT-DIA can both represent the diameter in millimetres of the optical aperture. F4W2HDU will detect the presence of a number of synonymous keywords, when:

A Keyword is selected and does not exist in the search target, but a synonymous keyword is found.

In the following example: EXPOSURE was selected from the Keyword Library List and is not found in the current header. But synonymous keyword EXPTIME was found and is highlighted in the header view.

EXPOSURE, EXPTIME and EXP-TIME, are all synonyms for the image property 'Exposure Time'. The relationship shown by the equivalence symbols and described by hovering the mouse cursor over the symbol.

Multiple Synonyms: There may be valid reasons for using two different keywords to represent exactly the same value in one header, so F4W2HDU will not stop you from inserting a keyword into a header that already contains a synonymous keyword. If this is to be done deliberately, care should be taken to ensure that the synonymous keyword values match.

Differing values for synonymous keywords may constitute a data integrity issue and may manifest issues with software that make use of that data. FITS4Win2 , will always look for a 'Base' keyword first and Synonyms next when providing metadata to Windows. This is described further below.

FITS4Win2 and Synonymous Keywords: The FITS4Win2 Property list contains all of the property names supported by the current version of FITS4Win2 and these are mapped to "Base" keywords in the FITS list. It is not necessary for a 'Base Keyword' to exist in order for FITS4Win2 to provide the correct metadata to a Windows image property if a synonym exists.

If your files contain synonyms to F4W2 Base Keywords, these can be updated instead of the Base Keyword and FITS4Win2 will use them.

See the table of supported Windows Properties with matching Base and Synonymous Keywords in the FITS4Win2 manual entry, FITS4Win2 Property Keyword List.

Planning Updates

New Update Plan entries are created from the current data in the Editor. Whenever a keyword is selected as described above, the keyword is placed into the Editor where it can be used as an update reference. For example, if a header record is selected from the displayed header, the header data is placed into the editor where it can be used as is to reference a deletion or insert. To update this particular value, the editor value must be modified from that in the header, prior to pressing the Modify button, to plan the modification. The process is described further below.

The Editor

The editor is the basis for all header updates If you want to Modify a header record for example. You must first click on the header record that you want to change. That record will automatically be put into the editor where you can change either or both of the Value or Comment components. Pressing the "Modify" button will then insert a plan entry to replace any header records matching the selected one, with the newly entered values from the Editor.


In the first column of the editor is a symbol representing the Editor data Status as shown below.

Value not yet used has not been saved to the Update plan.
Value has been used has been saved to the Update plan.
Value cannot be used is read-only and cannot be modified or used as an Update Plan entry.

Editing Data

Changes can be made to the Value by clicking inside the Editor if the current keyword is editable. Non-string values can also have the Comment field entered and/or edited independently of the value, by clicking the Comment section within the editor. The editor Value and Comment sections are aligned with the header grid above them (not shown).

Data from the Editor is used to plan one or more Insert, Modify or Delete actions, by pressing the appropriate button. The following table describes how each of the update types are applied to headers when the Update Plan is Executed.

Update Plan Tab

The Update Plan

Note All update plan entries are applied to files during processing. Any unwanted entries should be removed before processing.

The update plan contains each entry from the editor that was committed with one of the plan buttons. It can be reviewed and edited here prior to applying the plan to your files.

Hovering the cursor over an update plan entry will display it in a tooltip.

Column Possible Values Description
X Checked or Unchecked Used only for selecting entries for deletion from the plan
Keyword The target FITS Keyword The Keyword to search for during header update (Save)
In File Y or N Inserts will require that this Keyword does not already exist in the file.
Updates and Deletes will require that the Keyword does exist in the file.
with value 'Value to match' for Exact Delete or Update
'None' for inserts, 'Any' for Keyword delete
The Keyword must have this Value to be updated
becomes 'New Value' or 'Deleted' Keywords with the above Value will become this value
Type Update, Delete or Insert The type of this update

Apply Updates - Process Files tab

Here is where you apply the Update Plan to syour selected files. A running log can be opened, viewed and appended, or replaced. The output path for saved files can be selected and all other runtime options are here.

Applying updates to files

To Apply the update plan to files:

1. Select the files in the list that you want to process

2. Choose the Output path for saved files

3. Set any required Overwrite and Logging Options

4. Press the Start button

Checkbox Checked unChecked
Overwrite Existing Files Overwrite existing files without prompting Do not overwrite existing files.
Save Files if unChanged Save files that are unchanged after processing. Only save files that were updated during the run.
Load Files after Save After a file is saved, load it into the File list. Do not load saved files.
Save Log Save to the Run Log during processing.
Note that the "Append Log" checkbox also applies here.
Do not log execution.

Select the Output Path - On the Process Files tab, labelled TO.

Sets the path where files will be saved. It is displayed in the RUN section on the Process Files tab.

Path to save files
The output path for saved files can chosen by pressing the 'Folder' button.

Overwrite Notes: For safety, Overwriting files requires two settings. The "Overwrite Existing Files" checkbox above, must be set and the Output Path must be "Input". Input is specified by pressing the "Input" button on the right-hand side of the path display.

When a specific folder is chosen for output, all files will be saved to that folder.
Files can only be saved to either the original input folder (which can be arbitrary) or a single selected output folder, chosen by pressing the "Output" button.
It is possible when saving to a folder other than the input folder that files may already exist there. In this case, Overwrite must also be checked for newly updated files to be saved.

Program State - On the Process Files tab, labelled STATE.

State of the program
The State is a summary of current settings selected. The Planned and Files counts respectively show the number of Updates planned and the number of Files selected for processing. All other counts show results the previous execution and will be 0 otherwise.

Run Logs- On the Process Files tab, labelled Run Log Viewer.

Log Viewer
The run log summarises all processing done during previous executions. 'Append Log' determines whether the log will be overwritten, or appended-to when the 'Save' button is pressed to save the displayed log.

File Explorer Tab

The File Explorer is a fully compatible Windows 7 Explorer that can also be used to load files into F4W2HDU.
See the FITS4Win2 Explorer guide for examples.

Windows Explorer Layout
Layout and view settings are the same as described for Windows Explorer in the FITS4Win2 guide.
Loading FITS files from Explorer

Files can be loaded into F4W2HDU from the File Explorer, by selecting the files and dragging them into the 'Loaded Files' window, or right-clicking the files and selecting F4W2HDU from the context menu.

FITS4Win2 Tab

FITS4Win2-specific information

The FITS4Win2 Tab displays the installed package version and registration status at top-left. There are four informational tabs in the center panel two of which; Installation and Registration, are further described below.

FITS4Win2 Installation Tab

All installed components of FITS4Win2 are shown here along with the installed version. Updates for FITS4Win2 and F4W2HDU can be checked here, downloaded and installed if needed.

FITS4Win2 Registration If FITS4Win2 is installed, the version of each component is shown.

Standalone F4W2HDU installations will show "Not Installed" for all but the F4W2HDU version.

FITS4Win2 Registration Tab

If a FITS4Win2 license is found on the current machine, the registration name and code are displayed here. In the following example, a 14-day trial is active. The trial status is shown where registration details would otherwise be

FITS4Win2 Registration If you have purchased a license, follow the on-screen registration instructions to register your trial

Note the trial is never the latest version of FITS4Win2 which is license holders can download any time. A license includes the latest version which will replace the trial when installed.

To buy a FITS4Win2 license, click here

Displayed Tips

Almost every control on the form has tool-tips. Hold the mouse over anything to see what information is displayed, for a given control.

FITS Notes

FITS4Win2 has been tested with images from hundreds of sources. Including photographic images from amateur astronomers and professional telescopes like the Hubble Space Telescope and NOAO, as well as NRAO radio images.

Keyword definitions, values, data types, formats and implementations can vary and F4W2HDU tries to stay out of the way . For example:

Strings surrounded by single quotes - The application of quotes can seem arbitrary and haphazard across applications. F4W2HDU will leave quotes where it finds them, but will not add quotes to newly created string values. They may be explicitly entered as part of the string value.

Keyword Interpretation - For example, some software incorrectly use the APERTURE keyword to represent the aperture diameter in millimetres. APERTURE is defined as a string value representing the name of the aperture used and APT-DIA is the correct keyword representing a real number for the aperture diameter. F4W2HDU will correctly treat APERTURE as a string if edited, which means that if you need it to be a number for whatever reason, you can still enter a number value for it. APERTURE will not be treated as a Synonymous Keyword for APT-DIA, as it does not represent the same value.

Keyword source dictionaries - Where possible, F4W2HDU will display the source dictionary from which the keyword details were referenced. Although there are a number of identified synonymous keywords , there is probably a lot more, originally implemented for whatever reason, maybe a typo by a programmer. For example, FOCALLEN, FOC-LEN and FOCLEN all represent focal length in millimetres. Though all three have been identified within FITS files, not all have been identified in any specific FITS dictionary. F4W2HDU will treat all three as synonymous. Keywords from unknown sources are shown as being from library 'OTHER'.