Pages: [1]   Go Down

Author Topic: Confused About Image Sizes of Tiffs saved in Photoshop  (Read 325 times)

pflower

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 396
Confused About Image Sizes of Tiffs saved in Photoshop
« on: April 07, 2021, 02:27:34 pm »

I don't really use Photoshop very often, pretty much everything I do is in Lightroom.  When I do use Photoshop it is via the "Edit In" process from Lightroom and I don't pay much attention to what happens to the Tiff file after saving in Photoshop.  So I really don't know my way around Photoshop.

But recently I have been experimenting with digitising some negatives on a lightbox with a Sony A7R IV and I am confused about the file sizes I am getting.  Opening an .ARW file directly from Photoshop brings up Camera Raw.  I ignore all options in Camera Raw and just click on "Open".  I do what I need to do in Photoshop - i.e. invert the image, re-orientate it if necessary, run a B&W adjustment (these are all B&W negatives) and then save.  What I hadn't noticed is that the Image Mode was 8 bit Tiff.  But the Image Size dialog shows that the file 174MB  in size and at a resolution of 300 psi but the saved 8 bit Tiff is only 43.6 MB in size - although the info in the Finder (I am on Mac) is that it has the same pixel dimensions, is in 300 ppi.

Opening another negative from Lightroom via the "Edit In" command - which is set to open as 16 bit Tiffs and opens directly in Photoshop - ignoring Camera Raw.  The Image Size according to Photoshop - again at 300ppi is said to be 311MB.  But the saved Tiff is only 170MB or so.

Can anyone explain what is going on?  I have checked and both in Image Size and Canvas Size I have not inadvertently re-sampled to a smaller pixel dimension or size.

Thanks

Logged

Guillermo Luijk

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 1914
    • http://www.guillermoluijk.com
Re: Confused About Image Sizes of Tiffs saved in Photoshop
« Reply #1 on: April 07, 2021, 05:15:39 pm »

The only important parameter is image size (how many pixels of width and height it has). ppi is totally irrelevant until you print. The filesize in MB is variable since you probably are applying compression to your TIFF files, so you can't control it. I assume you are not confusing MB (filesize in your hard disk) with Mpx (pixel count), which are totally diffent things.

Regards

Doug Gray

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 2079
Re: Confused About Image Sizes of Tiffs saved in Photoshop
« Reply #2 on: April 07, 2021, 05:16:00 pm »

Tiff files can be saved either with no compression or compression such as Zip or LZW. Zip is usually, but not always, smaller. But unlike jpeg, these compressions are lossless. So when you load or print a compressed tif file, nothing is lost. It just takes less room on your disk.

But nothing's free. Unlike many files, when you Zip a compressed tif file, it's likely to not get further compressed at all.
Logged

Chris Kern

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 1549
    • Chris Kern's Eponymous Website
Re: Confused About Image Sizes of Tiffs saved in Photoshop
« Reply #3 on: April 07, 2021, 06:15:28 pm »

Are you comparing a file saved with two or more layers with a file that consists only of a single layer?

pflower

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 396
Re: Confused About Image Sizes of Tiffs saved in Photoshop
« Reply #4 on: April 07, 2021, 06:49:54 pm »

Definitely one single layer.  Compression might be the answer (where and how do you set compression when saving in Photoshop?). 

But I have two files - one an 8 bit Tiff which according to the Finder in my Mac is 48.6MB in size.  The other is a 16 Bit Tiff which according to the Finder in my Mac is (now) 144MB in size.   The original ARW RAW files iare both 122MB in size.  Photoshop has the 8 bit Tiff as 171Mb in size and the 16 bit Tiff as over 300MB.  How, on a simple "Save" command do you end up converting a 122MB Raw file into a 48.6MB Tiff without dramatically reducing its size - which I haven't done.

I have imported both of them into Lightroom and if I look at them in Library view via the metadata at the end of the Library panel they both have exactly the same pixel dimensions - 9504x6336.  If I set them up  to print in Lightroom at A2 size they both have the same native resolution in Lightroom at 426ppi.  But one file is over 3 times the size of the other.

This is just an initial experiment and so I am not going to bother to print them to compare differences on a final print, but I can't understand the disparity between the physical size that Photoshop identifies each file as having and the Finder's version.  Now I did run both through a desaturation action in Photoshop and a convert to B&W which presumably lost some colour information - but both are still in RGB colour space - which might explain the loss of some information.    But not so much.

The only explanation I can think of is that there is some bug or problem with the Mac Finder's interpretation of the file.  Both Photoshop and Lightroom have them as pretty big and robust files.

Anyone got any other thoughts?

Logged

degrub

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 1574
Re: Confused About Image Sizes of Tiffs saved in Photoshop
« Reply #5 on: April 07, 2021, 10:37:18 pm »

In the first case you use 1 byte (8 bits) to represent the grey scale and in the other 2 bytes (16 bits). This doubles the apparent file size.

Are you “scanning” the negatives as colour images and then converting or scanning  as grey scale ?
If colour, the R, G, B would represent an 8x increase in storage size for 16 bit versus 8 bit.
Logged

mcbroomf

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 1178
    • Mike Broomfield
Re: Confused About Image Sizes of Tiffs saved in Photoshop
« Reply #6 on: April 08, 2021, 06:07:57 am »

Whenever you do a Save As, and also the first time you do a Save, a dialog window pops up offering how the file will be saved.   Compression (and which type), Pixel Order ...   It could be that you just OK'd that on your 1st Save and didn't see it, but the posts above suggest compression.  Try a Save As, change the name and choose no compression and see what Finder gives for a file size.

As for why a 16 bit file and an 8 bit compress to different sizes (relative to their 2x files size difference).  I'm sure there's a good reason.  Does it matter?
Logged

digitaldog

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 17982
    • http://www.digitaldog.net/
Re: Confused About Image Sizes of Tiffs saved in Photoshop
« Reply #7 on: April 08, 2021, 01:11:13 pm »

Definitely one single layer.  Compression might be the answer (where and how do you set compression when saving in Photoshop?). 
http://digitaldog.net/files/TIFFvsPSD.pdf
Logged
Andrew Rodney
Author “Color Management for Photographers"

pflower

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 396
Re: Confused About Image Sizes of Tiffs saved in Photoshop
« Reply #8 on: April 08, 2021, 03:56:03 pm »

I'm not sure it really matters that much.  But it is confusing.

So, I have a DNG file which derived from an experiment in pixel shifting on digitising a B&W negative on an A7RIV.  That file is 159MB in  size.  I use the "edit in" command in Lightroom to process it in Photoshop as a 16 bit Tiff.  I do nothing in Photoshop to it except to invert from a negative to a positive and then save it.  The size of the 16 bit tiff is 214MB.  Not unexpected.

I then use the edit in command in Lightroom to send that 16 bit Tiff for editing in Photoshop but as an 8 bit Tiff - i.e. I have changed the external editing parameters in Lightroom to export to Photoshop as an 8 bit Tiff.  I do nothing in Photoshop to that file except to save it as a new 8 bit Tiff.  That new Tiff is just 26 MB in size - nearly 1/10th of the size of its source 16 bit Tiff.

Looking at both files in the Lightroom Print Module both seem identical in size i.e. both show that they have same number of pixels and will print at 15x15 inches at 426ppi.  But one is nearly 1/10th the size of the other.

So I then open the original (159MB DNG file directly in Photoshop).  That brings up ACR which I ignore and open in Photoshop.  I then save that from Photoshop  as an 8 bit Tiff.  The file size is 115MB - which given the original 16 bit Tiff was 214MB seems reasonable.  That too, in Lightroom, will print at 15x15 inches at 426 ppi.

So I am truly confused. 

So how on earth do I end up with a
Logged
Pages: [1]   Go Up