Pixels per Inch (PPI) is only used to calculate print dimensions. It is irrelevant for creating 3D textures, patterns..... anything that will be viewed on screen. All that matters is the overall pixel dimensions.
Dave, I really hope you understand what I am about to say. For two days now I have been a sponge for all manner of interesting information but none of it explains why Photoshop is giving me an incorrect reading. I cropped a random image as a 1024 x 512 pixel, 96 pixels per inch, graphic and saved it as DDS DXT1 (no Alpha) texture. I immediately closed Photoshop and sent the file to a friend. I then restarted Photoshop, examined the "Image Size" of the DDS file and it said it was 72 pixels per inch.
Pretty quickly my friend replied to tell me that his copy of Photoshop revealed it to be a 96 pixel per inch graphic and not 72 pixels at all. So, my copy of Photoshop is bugged OR I have neglected to tick a box somewhere and given the fact that I have spent a very intensive two day course in everything Photoshop I am at my wits end.
My friend also informed me that my file's data size was wrong. Apparently a 1024 x 512 DDS file saved at DTX1 with no alpha is always 256 Kb whereas mine was an odd 341 kb.
I can do nothing until this is fixed because I have no faith in the tools I'm using.
1 person found this helpful
I don't do any 3D work, so I can't comment on saving in the DDS format.
But as davescm has pointed out, PPI is totally irrelevant and meaningless for images viewed on screen.
PPI is not a property of the image - it is optional metadata that is used by printer drivers to calculate the printed dimensions of an image. So stop worrying about the PPI - it doesn't matter what number it is. The only numbers you need to worry about are the pixel dimensions.
The two images above are both 900 x 601 pixels.
One is 1 ppi and the other is 600 ppi, and they display identically.
As for the difference in file size that you mention - does it cause any problems that your file is 341 kb instead of 256 kb?
The value of 96ppi or 72ppi or 300ppi or 360ppi etc is just a value which is stored in metadata (i.e. a value stored in the file alongside the actual image data). It is used when printing to tell a printer driver how many of the image pixels it should use in every inch of printed output.
It makes no difference to file size. It makes no difference to pixel dimensions.
If you have saved/cropped the image as pixel dimensions - not inches or cm then whatever you set the ppi to will not change the file size, so that does not explain any variation in file size. The ppi changing on reloading the file suggests, as can happen with PNGs, that the ppi value is not actually being saved - hence the default re-applied on opening. This makes no difference - these textures will not be printed so any ppi value is meaningless.
A DDS file is a container that can contain 8 bit or 16 bit data in both compressed and uncompressed formats. If you are getting odd results it has nothing to do with a ppi setting in Photoshop.
As you said in your first line - what is important is getting the pixel dimensions correct - in your case 4096 x 2048.
72 ppi was the resolution of the old school 1984 MacIntosh monitors Photoshop was designed in. 96 ppi is the 1990s standard Windows monitor resolution. If the metadata can't be read Photoshop defaults to that number. My guess is that Photoshop can't read DDS resolution metadata and plugs in the 72 default.
So my question is, "do you keep that 96 when you move out of Photoshop or are they now 72?"
As been pointed, whether 72 or 96, that effects print size not screen size.
One interesting setting is under Preferences > Units and Rulers:
My Macbook Pro monitor has a screen resolution of 114 ppi. I set it there so when I use the command View > Print Size, I get the physical Print Size on screen. But as you might notice, monitor resolutions are all over the place.
Edit: created a 96 ppi file in Photoshop and it shows that everytime I open it. If I remove the Metadata in Save for Web, the file opens with a default of 72.
If that helps explain it.
It sounds like the 3rd party file format plug-in (NVIDIA Texture Tools for Adobe Photoshop) is not maintaining the resolution setting.
I took a quick peak at the web page for it (NVIDIA Texture Tools for Adobe Photoshop | NVIDIA Developer ) and it looks like it was last updated 06/27/2017 for Adobe Photoshop 5.0, 5.1, 6.0, 7.0, CS, CS2, CS3, CS4, CS5 and CS6.
Technically, as covered in prior posts, it's not a setting that matters unless you're doing something for print. Of course, if it's raising a red flag later in your workflow, you'll want the 96 dpi flag to remain.
I can think for three things to try:
- Reach out to NVIDIA and ask if they're going update the plug-in.
- Download and install Photoshop CS6 and save to the 3rd party file format from there. (PS CS6 should be available in Creative Cloud Desktop under "Previous Versions").
- Find out if a different format may be submitted and converted later (like PNG).
Thank you gener7, I think you may have hit on it. In my 'preferences' for "New Document Preset Resolutions" my screen resolution is set for 72 pixels per inch but I judged that to be for "new document presets" and therefore irrelevant. If I change that setting to 96 pixels per inch will all my DDS files show up as 96 pixels per inch even if they are not? That could be worse.
As for those of you who say that ppi is not important for the web, or for viewing on a screen, you misunderstand. These images will not be viewed on the web and not really on the screen either - not directly. They will be handled by a game engine and be manipulated to create objects and elements within a game and the rules for the textures are strict. Of course, I want the best quality just as I aim for the best file size cost to quality ratio but what I cannot have is inconsistency and ignorance. If an image is 3000 ppi and I open "Image Size" I want to see that it is 3000 ppi and not see 72. I sent three more DDS files to my friend. One on 150 ppi, one on 96, and one on 72 ppi. He opened them on his copy of Photoshop and he saw 150, 96 and 72. I opened them on mine and saw 72, 72, and 72.
I'm tired. I've been up for over 48 hours over this. The reason for that is that DDS DXT1 (no Alpha) files of 1024 x 512 pixels are always 256kb. These 341kb files are corrupt and are crashing the game engine. I spoke of the ppi issue not out of any concern for resolution or quality but because it seemed logical that more people would know how to fix a settings issue than how to stop corrupt DDS files from destroying my work.
Anyway, thank you again. I will test out the "Units and Rulers" preferences after I have had a sleep. I just don't think that is why I have corrupt DDS files.
You can ignore the Units and Rulers setting. I don't think that is the problem.
If your images somehow do not have the resolution metadata, Photoshop will assign 72 ppi whether it is Ps Windows or Ps Mac.
I can't see how the simple act of opening files can cause that loss for you and not your friend. Perhaps you can compare notes. Also if these images are being emailed, perhaps your email program or provider is removing the resolution metadata. Zip those files if they have to go anywhere.
Another point is that while it is true the PPI resolution metadata is not important for viewing, I get the idea that web designers use that figure because it's a constant and the easier way to call up a series of similar images. May be the code evaluates something and decides whether to call up the 150, 96, or 72 image.
I'll leave it at that.
Further testing gives me the following:
1) Saving images as PNG, JPG, or any other format gives no problems. If I alter the ppi for a JPG it shows up in "Image size" correctly.
2) It is only when I save an image as a DDS texture using the Nvidia DDS plugin does the pixels per inch change in "Image size" to 72 and the file becomes almost 50% bigger than it should be.
3) From feedback I have learned that textures saved at 96ppi stay at 96ppi. The problem is that Photoshop is misreporting this information. The critical problem is that a 341kb (rather than 256kb) 1024 x 512 DDS texture is unusable.
4) In three days of intensive investigation, I have found no other instance of problems like mine. I know many people in my field that use the Nvidia DDS plugin and none have come across this.
Well it seems to point at something going on with the plugin. Maybe a preference setting or install issue?
Have you contacted Nvidia or their forums about this? Perhaps there is an update or a fix to this issue.
If you do suspect something off with your copy of Photoshop, perhaps a Preferences reset would clear it.
You could open a new user account on your computer to eliminate anything on your own account causing problems.
Thank you gener7, you are indeed a champion. Mainly because I didn't always have this problem. The plugin worked just fine for many months and I only discovered the issue a few days ago. Well, I "Reset Preferences on Quit" as you suggested. No luck, I'm afraid. I did discover that the 1024 x 512 DDS files are now 256Kb as they should be and it is possible that I was creating mip maps or something similar that was creating the discrepancy.
However, the bottom line is reliability. I want to trust what Photoshop reports and when I see 72 pixels per inch I do not but since my account is connected to my ISP email address, creating a new user account will be a last resort. Therefore, I am now on the Nvidia Forums annoying them. However, I believe the answer is not a bug. I have a sense that it is something that I have done or have missed that is so obvious to the professionals here and at Nvidia that no one has thought to mention it. That is, in the sense of, "Your computer is switched on, right?" Anyway, I shall continue my search. And, thank you.