File size question after processing HDR photo.

I never noticed this before, not sure why. After processing photo and filing it, I noticed that the picture went from a single photo of 300dpi to 72 dpi after processing 3 photos..

DPI has been confusing to me, but apparently it is not important on its own.
I can't answer your question, but I saved these article about dpi.

All About Digital Photos - The Myth of DPI
Other small articles on this site under the DPI tab.

and this one:
Dpi, misunderstandings and explanation, what is dpi

Just-Clayton said:

I never noticed this before, not sure why. After processing photo and filing it, I noticed that the picture went from a single photo of 300dpi to 72 dpi after processing 3 photos..

Click to expand...

What program are you using, and what file type are you saving it as? I suspect there's something in the program preferences, either the sending program or the HDR program, that has this set at 72 as a default. Should be easy enough to find and change.

In LR there's an "External Editing" tab in the Preferences options, but it only controls how the file is sent to an external editor or Photoshop. So I suspect that it's set either within your HDR program, or it's the default for the file type in your Save options.

If you use Adobe "Save For Web" to write your JPG file, it removes all Exif data, which is where the dpi number is stored.
72 dpi is just the value Adobe shows when there is no dpi number. It is NOT 72 dpi, it is blank. Just Adobes cute way.

If does not matter what that dpi number is or isn't, not until the time you press the File - Print menu selection. Then you will fix it first, to specify the size you want to print. In camera images, the ONLY USE for the dpi number is to space the pixels on printed paper, at like 300 pixels per inch (determines size of the print, on inches of paper). On the monitor screen, dpi is 100% ignored in all cases, it could not matter less.

The digital image is dimensioned in pixels... You can resample it to be more appropriate size for your use, but when you write the JPG file, the pixel dimensions remain the same, no change. It could not matter less for video monitor purposes what the dpi number is or isn't. This is why Save For Web removes it, it simply does not matter on the monitor screen. What does matter is the dimension in pixels, which is not affected unless you resample or crop it.

Pixels, Printers, Video - What's With That?

I printed a large HDR image before and it came out great!. I was just surprised when I looked at dpi. I was just wondering.

BackdoorHippie said:

What program are you using, and what file type are you saving it as? I suspect there's something in the program preferences, either the sending program or the HDR program, that has this set at 72 as a default. Should be easy enough to find and change.

In LR there's an "External Editing" tab in the Preferences options, but it only controls how the file is sent to an external editor or Photoshop. So I suspect that it's set either within your HDR program, or it's the default for the file type in your Save options.

Click to expand...

l. When I use core. When I transfer single photo it is 300dpi. So, I will see if there is a default.

If you are not printing the image and just posting on the web then your file size is significantly smaller if you export it to jpg at 72dpi. The files are huge if you use 300dpi and what you actually see on the web e.g this forum is still exactly the same in fact they could be less sharp as they will be reduced in size by the web site sw. As WayneF said the 300 dpi is only used for printing.

wornish said:

If you are not printing the image and just posting on the web then your file size is significantly smaller if you export it to jpg at 72dpi. The files are huge if you use 300dpi and what you actually see on the web e.g this forum is still exactly the same in fact they could be less sharp as they will be reduced in size by the web site sw. As WayneF said the 300 dpi is only used for printing.

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Not necessarily, but it may be more confusing to comment. There are so many ifs and buts about dpi.

If we were creating images by scanning, then yes, 300 dpi creates a greatly larger image than 72 dpi. If scanning 10 inches of paper, 300 dpi creates 3000 pixels, and scanning at 72 dpi creates 720 pixels. Dpi is extremely important to scanning, but that is about scanning.

Digital cameras create images a different way, and digital camera users can generally say dpi has no meaning whatsoever to them, but there is the local printing issue (on our own printer) that is an exception. The digital camera does not use dpi at all. It simply creates a 12 or 24 or whatever megapixel image, which is only dimensioned in pixels. Dpi is of absolutely no concern to the camera, it has no clue what size we might print it someday. The camera simply marks it with some very arbitrary dpi number, which has absolutely no significance. Also Adobe Raw marks it with an arbitrary dpi number, one which we can arbitrarily specify. It is just a feel good number, so we see it predicts to print smaller than a few feet size (which it would say if we let Adobe run with their made up 72 dpi number when it is blank). But Save For Web discards any dpi number, regardless of what it was (because video systems have no use for the number).

When printing it (for example, an internet printing service), we specify that we want it to be say 8x10 inches, in which case dpi is of no concern, and is not used. Regardless of the dpi number, they simply print it to be 8x10 inches. The process will compute some new dpi number so the print dimensions come out 8x10 inches, from the pixel dimensions that we have. The number of pixels (dimensions) is the valid concern. We do want that number to come out around 300 dpi ballpark, denoting good quality.

Or, if on our own printer, if we just say Print, this is the only time the dpi field will be used. It will determine the print size that way (sized to be so many pixels per inch). Or instead (if we say MORE than Print), our printer dialog may offer the opportunity to instead specify 8x10 inches, instead of using dpi. It should tell us the resulting dpi number in that case. We are concerned that we are printing up around 300 dpi, but this is the only use for the number. It denotes print size. 3000 pixels printed at 300 dpi will cover 10 inches of paper.

For a video monitor image (including web pages), dpi has no meaning whatsoever (no video system uses dpi, screens are dimensioned in pixels, and images are dimensioned in pixels). And any Save For Web output will discard dpi information. Dpi will be blank (and Adobe will tell us it says 72 dpi, but Window Paint and others will tell us it says 96 dpi. But it is still blank, if Save For Web.) Dpi has no use on the video monitor screen. We simply could not care less what dpi says on a video monitor.
The uptight guys will want to comment on calling it ppi, but it is the same thing.

If we RESAMPLE an image that says 300 dpi to instead be 72 dpi, it does get much smaller (image pixel dimensions).

If we SCALE it (simply change the dpi number without resampling), it has zero effect on the video monitor image. Still the same size in pixels. But it might print a different size then (depending on how you printed it).

The Adobe Resize box has a checkbox to turn off resample (to be scaling), or to resample it. We do all seriously need to understand this part.

For digital camera images, forget about dpi, with the one exception of when dpi determines print size, instead of just saying to print it to be 8x10 inches.

Thanks for the detailed explanation.

I am very nervous of using an external printing service as not only do you need to worry about the number of pixels for large prints but also the color space.
Color space can be a minefield and the printed version you get back loses all the vibrance you see when looking at the picture on your monitor.