Data loss with TIFF format

[Tim]

I have been reading through the various resources on line (wikipedia and its external links seem the best) regarding the TIFF image format, but there is still one question I'd like to be 100% sure of:

If I open an 8 or a 16 bit TIFF, and alter the data in the IPTC meta tags, then re-save, does the image data get altered IN ANY WAY AT ALL ??

Tim

[Dave Humphries]

Hi Tim,

I'd say that is largely dependent upon what you open it with (e.g. which image editor).

... but having said that, I'd be very surprised if it did,

... and having said both those things; I'm sorry I cannot help further, as I don't use the TIFF format.

If you let us know which editor you were considering (or doubting), someone else may be able to confirm.

Cheers,

[Steaphany]

I use 48 and 96 bit per pixel (16 and 32 bit per channel) Tiff format files in my process flow, especially when working with astronomical photography.

I have AIP4Win which is capable of a range of image analysis and comparative operations.

If you can get me a before and after set of Tiff files, I'll compare them in AIP4Win to see if any of the image content varies.

[Tim]

I'm using Photoshop CS3 to open, edit, and save files.

Steaphany - I have sent you a private message requesting contact details.

Tim

[Colin Southern]

Put it this way -- *.TIFF is a lossless format (even with compression) - so I wouldn't expect the image data to change.

[kevinf]

Colin is correct, TIFF is lossless as long as you don't use the jpg compression option in photoshop (which makes it a jpg in a tiff container)

[Steaphany]

Given two 48 bit per pixel images, I performed three sets of mathematical manipulations

• Subtraction
• Difference
• Exclusive Or

In all three cases, there was no variation between the source images. Both were completely identical.

[Tim]

I'm assuming Steaphany is talking about the 2 images that I forwarded - identical except that one was re-opened, some data was added to the IPTC tags, and the image was then saved under a new name. All seems to be OK then - this means that I can prepare my images as TIFFs, then add the IPTC tag data at a later date.

Thanks to all - you've been very helpful,
Tim