"Save As" Tiff to Jpeg then back to Tiff again!

  javaBalls 16:29 15 Sep 06
Locked

A friend of mine takes digital photographs in TIFF format. The images tend to be around 18 MB in size and 300 dpi.

Sometimes he emails them to clients. His clients require high resolution images. However due to the large size of TIFF files he converts them to JPEGS using the “save as” option in Photoshop.

Once the image is in JPEG format it is reduced to around 2 MB in size. From what I understand this is a lossy compression – the information is lost. However it’s still at 300 dpi?

Now here’s the funny part. He tells his client to convert the JPEG that he’s emailed back to a TIFF. He’s thinks they’re getting the same TIFF. Surely not. They’re just getting a new TIFF.

It is impossible to restore the image to the original TIFF because information is lost after the first conversion.

However when the “save as” option is selected and save from a JPEG to a TIFF it increases to around 17 MB. But it’s still 300 dpi. I’m a little confused about the extra size. Where’s the information coming from?

I think there’s no point trying to convert back to a TIFF because the JPEG is sill 300 dpi. But how is it still 300 dpi when it’s lost around 16 MB of data?

Am I right to tell him that you cannot recover the original image from the JPEG?

I think he should zip the TIFFs instead.

Does anyone support my view?

  terryf 16:32 15 Sep 06

Yes

  DieSse 18:09 15 Sep 06

*Am I right to tell him that you cannot recover the original image from the JPEG?*

Yes you're absolutely correct.

A Zip will not lose any information, however, and may help to compress the file. ALZiP is an excellent free Zip program click here

The dpi is a different matter from the file size and information contained in the file. When a picture is compressed with a jpeg compression algorithm, it leaves the original number of dots in the file, but by altering the amount of variations in shade between them, can reduce the file size. Other techniques are also used in the compression - the aim though is to preserve the picture size and shape and just compress the data.

  Jak_1 20:31 15 Sep 06

There is another solution, he could upload to click here (for free) and email his clients with the url. They can then get the full quality original TIFF piccies.

  javaBalls 13:46 16 Sep 06

Jak_1- I'll tell him to use a site so that cilents can download the image using a URL.

DieSse - thanks for the dpi information and the zip program

Thanks for the clearing this matter up for me. It was more a check for my own sanity.

Can you clear up the final issue? - we agree that you can't restore the original tiff. Therefore is it complete waste of telling his customers to save the JPEG as a TIFF?

  Jak_1 14:10 16 Sep 06

Once the original TIFF has been converted to a lossey JPG (having lost x amount of data)it can be converted back to TIFF but still at the expense of the lost data ie it will not have the same resolution as the original TIFF but that of the lossey jpg.

  X™ 14:15 16 Sep 06

Jak_1 summed it up. It's like, I'll get this ammount of Tuna, compress it, squeeze out all the water, then give it to someone, they can decompress, add water, but it's not the same quality. If you get me ;)

  javaBalls 14:21 16 Sep 06

thanks Jak_1 and X™.

I like the tuna comparsion. :-)

I'll tick this as resolved now.

thanks

  DieSse 14:43 16 Sep 06

*Therefore is it complete waste of telling his customers to save the JPEG as a TIFF?*

It's not just a waste of time - it actually makes things even worse. Every conversion involving lossy formats will lose something more, whichever way it's done.

If zipping produces a useful saving, he can, of course, still send the files as zipped email attachments. Saving to the web doesn't improve the process in any way (though it may get around some email capacity limits if there are any in this case).

  DieSse 14:47 16 Sep 06

ie it will not have the same resolution as the original TIFF but that of the lossey jpg.

Saving as a jpeg does affect the quality of the image - that doesn't mean the "resolution", which is a different factor and means something else in digital terms.

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