TIF file size?

[LunaLuna]

Hi everyone,

I client sent me a tif file for a few fixes. I worked on it with Photoshop and saved again as tif.

The original tif file is 67 MB and the one I saved after fixing is only 19Mb.
I don't understand why that much difference…

Characteristics of both files:
Format: tif
Size: 2528 × 3743
Color space: Gray
Color profile: Gray Gamma 2.2

I'd appreciate if someone can explain that difference… I'm maybe doing something wrong?

Thanks in advance!
Lucia.

[Tony W]

Re: TIF file size?

A Grayscale image of those pixel dimension as 16 bit TIFF would be around 18MB and 32 bit approx double. So your file size of 19MB does not sound unreasonable.

Is the original file layered and/or been saved as 32bit?

[klev]

Re: TIF file size?

There are various things that can affect the size of a TIFF file. Photoshop offers either Lempel-Ziv-Welch (LZW) or run length encoding for image compression, but that file size sounds like it is uncompressed. Assuming 8 bits per channel on a single channel image, you start with 1 byte per pixel, 2528 * 3743 pixels / 2^10 bytes per KB / 2^10 KB per MB.

That leaves you with roughly 9MB of information required to store one channel not counting any file headers, tags, etc. I could look up the TIFF specification for file storage, but this is not unrealistic. If it was previously stored in RGB, you would have 3 channels, each containing that amount of information. Saving at 16 bits/channel just means 2 bytes per pixel per channel.

[mistermonday]

Re: TIF file size?

It is likely that your client sent you a 16 bit uncompressed tiff and you likely converted down to 8 bit, likely compressed.
The math is pretty straight forward. Your image is just under 10 million pixels. An RGB Tiff file needs 3 bytes per pixel in 8 bit precision and it requires 6 bytes for a 16 bit precision. That means the tiff file would have been approx 30MB or 60MB. If you compress the 30MB file when saving, it could compress to approx 20MB. If you compress the 60 MB file it will actually increase in size to between 100-120 MB. Yes 16 will actually grow the file size using std LZW compression.
The only other way that your orig Tiff could have been 67MB and still in 8 bit would be if it had layers or alpha channels in it as a result of someone else's work on the file.
Cheers, Murray