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Walter, I just don’t get your dpi comments.
Walter,
I am having a hard time understanding (or agreeing with) the comments you have made about dpi settings in relation to still images that are used with FCP.
In an earlier thread, you stated the following in response to Rafael’s statement:
[rafalaos]
“Walter,
This is completly wrong. If you make two documents in Photoshop with the same number of pixels, the size of the file is the same. The dpi it doesn’t matter.”[Walter]
I’ve been creating animations in Photoshop and After Effect for 10 years now and as I have always seen, the higher the dpi, the larger the file size.We do this all the time with our animations, creating a character in 300 – 600dpi in Photoshop working in a very large frame size with a lot of resolution so we will be able to zoom in once I move into After Effects.
Once we’re done, we drop the dpi to 72 but we don’t allow Photoshop to ReSample the image. This drops the file size by around 50 – 80% depending on how many layers are in the file.
[end]I have an image in Photoshop CS3 Extended with the following properties (width: 1920 pixels, height: 1080 pixels, document size–resolution: 72 pixels/inch) [note ppi, not dpi], and I save that image (psd or tiff). I then Save As to another image (also psd or tiff). This second image is very similar in size (bytes–according to Finder). For this second image, I then use Image > Image Size to change the ‘document size–resolution’ from 72 ppi to 300 ppi (leaving Resample Image unchecked). The image remains at 1920 pixels by 1080 pixels. Of course, the document size in inches changes, but not the pixel size. I then save the document on top of itself. Finder shows little change in the file size (bytes).
If I open these two image files into Preview and select ‘View > Actual Size’ for both images, the two images look identical in size IF the preference ‘Respect image DPI for “Actual Size”‘ is unchecked. With this preference checked, the 72 ppi (or dpi, as reported by Preview) image apears much larger on the screen than the 300 ppi image when both are viewed at “Actual Size.”
Without doing extensive tests, I did try putting a 72 ppi TIFF on a FCP timeline next to a 300 ppi TIFF ([basically] same except for ppi). I applied some transformations to one and then copied those attributes to the other image. A rough check on render times and quality did not show much, if any, difference between the two.
Walter, please look at the section “Video Is Not 72 Dots per Inch” on page III-370 in the FCP6 User Manual.
Steve Grimes
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19 Replies
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There’s no reason at all to exceed 72 DPI unless its for print work. Video gets no benefit unless your photo program requires higher dpi to enlarge.
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DPI has no meaning in video. At all. Whatsoever. The only time DPI matters is when you’re going to a physical medium.
That’s why there aren’t any DPI buttons or menus in After Effects, Final Cut, etc… 1920×1080 pixels is ALWAYS 1920×1080 pixels regardless of your DPI settings in Photoshop. I can’t say why PS has larger file sizes for different DPI, but a pixel is a pixel is a pixel.
I’ve always heard people bandy about that video = 72dpi. It’s like an old wives tale that got started by a vicious misconception.
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CharlieX,
I agree.
I’ll add that file sizes (in bytes) don’t seem to increase to any sizable degree as [only] ppi (dpi) increases in Photoshop–as long as the image is not resampled. (i.e., if the number of vertical pixels, the number of horizontal pixels, the number of bits per channel, and the number of channels all remain constant, then I say the file size (bytes) remains (approximately) constant.
Steve Grimes
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I’ll give you a perfect example of what I’m talking about.
For our animations we often scan in an image off a printed page. We generally scan these at 600 – 1200dpi so we can get a very large pixel count, something like 1500×1500 to 2500×2500, allowing us to zoom in.
We clean up the graphic, add the character heads, break the image apart so we can animate. Generally we end up with a 45 – 150MB file.
Now we take that exact same image and drop it down to 72dpi, but don’t resample the size so it remains say 2500×2500. The new file is generally 20MB or smaller. So we send that character file into After Effects instead of the original, much larger file.
Walter Biscardi, Jr.
Biscardi Creative Media
HD and SD Production for Broadcast and Independent Productions.STOP STARING AND START GRADING WITH APPLE COLOR
The new Color Training DVD now available from the Creative Cow! -
[CharlieX] “DPI has no meaning in video. At all. Whatsoever. The only time DPI matters is when you’re going to a physical medium.”
I have seen instances where files that are 50dpi or less in resolution simply don’t hold up, even at 100% scale in video projects. 72dpi is a good rule of thumb to ensure that the resolution is enough that the graphic remains clean in a video app.
Walter Biscardi, Jr.
Biscardi Creative Media
HD and SD Production for Broadcast and Independent Productions.STOP STARING AND START GRADING WITH APPLE COLOR
The new Color Training DVD now available from the Creative Cow! -
Walter, thanks again for for sharing your working experience. I was quite in the dark about how to proceed effectively with larger PSD files for animating and zooming – scan size and dpi.
BTW – love your blog. Just re-read your entry about your rewiring project with Bob Zelin. Great read.
Garth A.
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If you’re talking about SCANNING, then yes, DPI matters on acquisition. Scanning art at 50dpi will yield garbage.
I think what confuses some people is that once you have a digital still, a tiff or psd or png, all that matters in your video apps is your pixel count. 720×486 pixels. You can save that as 50dpi or 1000dpi, but it will still be 720×486 pixels and will be indentical in FCP.
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Walter,
I still don’t get how your files are decreasing in size, if only ppi is changed. Maybe I don’t understand how Photoshop is handling text rasterization or something.
To humor me, take an image (e.g., 2500 pixels x 2500 pixels, 600 dpi) that you created from a scan process. Name that file Sample_1.tif, for example. Now open the ‘scan’ file (Sample_1.tif) into Photoshop. Save that image to a new Photoshop file, Sample_2.psd, paying close attention to the save settings (file type, layers, etc.). Close Sample_2.psd. Use Finder to determine the file size (bytes) of Sample_2.psd. Open Sample_2.psd into Photoshop. Now, Save As to a new file, Sample_3.psd, using the same save settings that were used to save Sample_2.psd. I assume Finder will show Sample_2.psd and Sample_3.psd to be similar sizes (bytes). Now, for Sample_3.psd, use Image > Image Size to change document size–resolution to 72 ppi, making sure that ‘Resample Image’ is first unchecked. Pixel dimensions should remain unchanged. Look at Image > Image Size again to verify that ppi did change. Save Sample_3.psd on top of itself. Check Finder to see if the file size (bytes) of Sample_3.psd decreased dramatically or remained roughly the same.
I didn’t try this procedure with a file such as yours–my sample file was a small file with some text layers and maybe some shape layers. I didn’t note a dramatic change is file size when I only changed the ppi setting.
Walter, I wonder if you read the FCP6 User Manual section I suggested.
(At the risk of violating copyright: “The dimensions of a video image are dependent only on the number of horizontal and vertical pixels used in the image. Pixel dimensions alone
determine the resolution of a video image. You can easily test this yourself by
creating two 720 x 480 images in a still graphics program, setting one image to a
resolution of 300 dots per inch (dpi) and the other to 72 dpi. Import both images into
Final Cut Pro and compare the two. They are absolutely identical. This is because
video editing software does not use the dpi setting of a graphic image.”
[FCP 6 User Manual, p. III-370]Steve Grimes
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I forgot to mention again that I did my simple test using Photoshop CS3 Extended. I don’t know if the version of Photoshop matters.
Steve Grimes
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[CharlieX] “DPI has no meaning in video. At all. Whatsoever. “
Hi
In the depths of pre-history Adobe Premiere 3-6.5 imported 10 inch wide images correctly, creayting a 720 pixel wide image, importing the same pixel-size image at 300 dpi produced a quarter-size import surrounded by black.So to Adobe in that era, only 72dpi images imported as expected. I don’t know if Adobe still maintains that workflow in PPro.
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