using convert.exe on B/W-Image swaps backgroundcolor
Posted: 2009-04-01T11:35:19-07:00
Hi there,
If you use convert.exe (version 6.5.0) to convert a black&white BMP to a TIF the TIF-tag 262 (PhotometricInterpretation) is set to 1 (Black is Zero).
Definition: For bilevel and grayscale images: 0 is imaged as black. The maximum
value is imaged as white. If this value is specified for Compression=2, the
image should display and print reversed.
So far this works OK and there is no problem.
(e.g. convert c:\picture.bmp c:\uncompressed.tif) where picture.bmp is a black&white BMP-File
If you add Group4 Compression to the resulting TIF the file is compressed but it will be shown (and printed) in reverse.
(e.g. convert -compress Group4 c:\picture.bmp c:\compressedGroup4.tif)
Please note that some viewers (as IrfanView or Microsoft Document Imaging) display the TIF correctly. Other viewers (like Microsoft Windows Picture and Fax Viewer) display the picture in black.
So in my opinion this is a bug as the use of Group4-compression does not consider "Black is zero". In earlier versions (like 6.2.5) the PhotometicInterpretation has been set to 0 (White is zero). This might be a reason why this bug never showed up.
If you use LZW compression on the other hand the image is still set to "Black is zero" but will be shown correctly. (e.g. convert -compress lzw c:\picture.bmp c:\compressedLZW.tif)
greets
Pikachu
If you use convert.exe (version 6.5.0) to convert a black&white BMP to a TIF the TIF-tag 262 (PhotometricInterpretation) is set to 1 (Black is Zero).
Definition: For bilevel and grayscale images: 0 is imaged as black. The maximum
value is imaged as white. If this value is specified for Compression=2, the
image should display and print reversed.
So far this works OK and there is no problem.
(e.g. convert c:\picture.bmp c:\uncompressed.tif) where picture.bmp is a black&white BMP-File
If you add Group4 Compression to the resulting TIF the file is compressed but it will be shown (and printed) in reverse.
(e.g. convert -compress Group4 c:\picture.bmp c:\compressedGroup4.tif)
Please note that some viewers (as IrfanView or Microsoft Document Imaging) display the TIF correctly. Other viewers (like Microsoft Windows Picture and Fax Viewer) display the picture in black.
So in my opinion this is a bug as the use of Group4-compression does not consider "Black is zero". In earlier versions (like 6.2.5) the PhotometicInterpretation has been set to 0 (White is zero). This might be a reason why this bug never showed up.
If you use LZW compression on the other hand the image is still set to "Black is zero" but will be shown correctly. (e.g. convert -compress lzw c:\picture.bmp c:\compressedLZW.tif)
greets
Pikachu