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|| SportsShooter.com: Member Message Board
image file resolutions
Mike Anzaldi, Photographer
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Oak Park | IL | USA | Posted: 11:12 AM on 02.14.11 |
->> can someone set me straight about the PPI coming out of the camera in RAW? i use a 5Dmark2 in the studio for product images. sometimes the client specifies a DPI for the files. one group prefers 600 DPI at actual size. I've always gone about this by simply cropping the image at 600 PPI in Photoshop, though occasionally the graphics guys will be unsatisfied. is there some element of file management i'm not totally understanding here? i know of no way to modify the resolution of the files coming out of the camera- which appear to be 240 PPI. can i get a better explanation of how this works?
is DPI/PPI only relevant when printing an image? |
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Marshall Smith, Photographer
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Stamping Ground | KY | USA | Posted: 1:08 PM on 02.14.11 |
->> I also shoot a 5Dmark2, and from what I understand about resolution, 21 megapixels will give an image of 15.6" X 23.4" at 240 pixels per inch. Without adding any more pixels by resampling, to use all these pixels at 600 ppi requires an image of 6.24" X 9.36", so I suppose that that size would be what the graphics guy wants.
I'm sure some of the other guys will set us both straight shortly if this is not correct. |
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Mike Anzaldi, Photographer
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Oak Park | IL | USA | Posted: 1:14 PM on 02.14.11 |
| ->> that sounds spot on. maybe the graphics guy is used to medium format image sizes. so, you don't really change the PPI coming out of the camera? it is what it is, which is fixed at 240 PPI? |
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Butch Miller, Photographer
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Lock Haven | PA | USA | Posted: 1:39 PM on 02.14.11 |
->> PPI is not set at all by the RAW image file ... the RAW data is just so many pixels data captured by the sensor ... resolution of that file is a choice or preference you choose with your RAW converter when it is time to "render" those pixels at a the dimensions you prefer .... while the camera may place a tag in the image file that can be read by proprietary software for a specific resolution ... in a RAW image ... when you render those pixels into another image file format (jpeg, Tiff, PSD, etc.) ... the ppi you chose comes into play ...
The density of pixels-per-inch is a preference for the output device of choice ... many folks prefer a resolution of 240 ppi for standard inkjet prints, 300 ppi for standard RGB lab prints ... some users prefer 360 ppi for some of the higher gamut inkjet printers that offer multiple ink sets ... and a myriad of other combinations based upon the capabilities of the output devises and the apparent IQ of the finished product .... |
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Marshall Smith, Photographer
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Stamping Ground | KY | USA | Posted: 1:41 PM on 02.14.11 |
| ->> In the Camera Raw dialog that opens up in Photoshop, if the Show Workflow Options box is checked, you can choose the resolution that will be used when the file is opened. I think 240 is the default option. |
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Mike Anzaldi, Photographer
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Oak Park | IL | USA | Posted: 1:57 PM on 02.14.11 |
| ->> so, if i open a RAW image at 240 PPI and resize it to reflect 600 PPI, is that the same as setting Photoshop to open RAW images at 600 PPI-- or have i added a step that will result in a loss of quality? |
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Marshall Smith, Photographer
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Stamping Ground | KY | USA | Posted: 2:15 PM on 02.14.11 |
->> If you keep the size in the menu the original to the camera (5Dmark2 is 5616 X 3744) then it should be the same.
And what Butch says about output devices. |
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Mark Loundy, Photo Editor
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San Jose | CA | USA | Posted: 2:49 PM on 02.14.11 |
->> There is no Pixels Per Inch (PPI) until you have inches to apply the pixels to. Until a reproduction size is specified, you only have absolute pixels.
For example, if a file is 100 x 100 pixels and it's reproduced at 2 inches x 2 inches, then the file is 50 PPI.
Whether a given file supports a specified resolution (PPI) depends upon how many pixels are actually in the file. You can make a file any PPI you want, but the higher the PPI, the smaller the possible reproduction size. The underlying file will not change at all.
There have to be inches before there is PPI.
--Mark |
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Clark Brooks, Photo Editor, Photographer
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Urbana | IL | USA | Posted: 2:49 PM on 02.14.11 |
| ->> My first question is who told you they need the file at be 600 ppi? Second, what is the end use? |
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Butch Miller, Photographer
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Lock Haven | PA | USA | Posted: 2:57 PM on 02.14.11 |
->> Well ... you likely would prefer 600 ppi if the print production used is a 300 lpi (lines per inch) screen for CMYK offset printing ... which is used on many high-end press units ...
Double the pixels per line screen is usually the preference ... while the use of 300 lpi isn't the norm ... it is still used in some mediums ... |
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Israel Shirk, Photographer, Assistant
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Boise | ID | US | Posted: 3:09 PM on 02.14.11 |
->> Cameras shoot in pixels. Resolution translates pixels to inches. Inches go on paper.
So... If they want a dimension at a certain resolution, you would resize or crop to that dimension and resolution, then apply your usual amount of sharpening. You can just type in an inch size and resolution into the crop box.
If they just want a certain resolution, without specifying a physical size, tell them you need to know what size it needs to be.
If they balk, they're the idiots in the situation; just give them a file that has whatever PPI set in camera raw. It's just to humor them.
If they need a stupid-high resolution (ie, 8x10 at 1200dpi), just resize it. Unless you're shooting medium or large format digital, you're not going to have a high enough pixel count. Just resize and sharpen as appropriate. |
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Mike Anzaldi, Photographer
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Oak Park | IL | USA | Posted: 5:05 PM on 02.14.11 |
| ->> i understand it. big thanks. |
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Paul Alesse, Photographer
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Centereach | NY | USA | Posted: 6:54 PM on 02.14.11 |
| ->> The disconnect seems to be in whether Mike's editor is asking for DPI or PPI. 600 PPI is an awful stretch... literally! Unless we are talking about a file that measures around 4 x 6, the interpolation of pixels at 600 PPI on a larger print, 8 x 12 or so, can get messy. Plus, 600 PPI is overkill. All it will do is pack file size on that JPG... anything above 300ppi isn't going to make a noticeable difference to the human eye. I'm not clear on what exactly the editor is requesting or what the rationale is. |
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Mike Anzaldi, Photographer
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Oak Park | IL | USA | Posted: 10:50 AM on 02.15.11 |
->> thanks kev-
the 'horrible DPI mistake' is good info.
here's the deal...i'm getting a second hand request from the client. the folks in graphics want their images "shot at 600 DPI, actual size". obviously, it's the "shot at" request that threw me. i capture the product images in RAW. i didn't think there was a way to specify what DPI the camera captured at. sounds like i'm right about that.
maybe they are making the request because of the printing method they use. i really don't know, and haven't been granted access to the dude making the request in order to learn myself what the hell it is they actually want. the products are pens/pencils/markers, etc. and they are being used for packaging, catalogs, retail displays, etc.
i certainly didn't know enough about DPI/PPI to question the client. i simply set the PPI in the crop window and save the RAW file as a TIFF. done. as has been suggested, i've stopped doing this and now changed the PS default from 240PPI to 600PPI when PS opens the RAW image. they end up getting a full-size image of a pen that is 8" wide. since the pen is actually about that size, i'm thinking this satisfies the request of 600DPI @ actual size. obviously, i have zero interest in arguing this stuff with the graphics department. based on the info in the link kevin suggests, the graphics guy is probably a little old school. |
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Mike Anzaldi, Photographer
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Oak Park | IL | USA | Posted: 11:00 AM on 02.15.11 |
->> kevin- also, your first sportsshooter link explains why resampling/resizing and sharpening are bad.
what it doesn't explain is how to crop and reduce file size for newspaper use without doing harm to the image.
some of my newspaper/wire clients have actually requested 10" max dimension @ 200PPI...exactly what this essay insists not to do. sooo...what to do? |
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Kevin M. Cox, Photographer, Assistant
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Galveston & Houston | TX | US | Posted: 6:11 PM on 02.15.11 |
->> Mike, basically any time you resample (reduce or enlarge the pixel data) and especially when you save as JPG you are harming the image. For me the key is to just reduce this harm as much as possible.
For that newspaper/wire you will have to do some "harm" simply to conform to their specifications. My suggestion is have the images set to 200 PPI at the start (either through Photo Mechanic or the RAW dialog of PS) and avoid changing the size until the very last step (or second to last if you feel the need to sharpen after reducing).
Once you've cropped and toned then go ahead and reduce (I recommend never increasing if you're already below the requested size) the print size to 10 inches using the Image Size dialog. You'll need "Resample Image" selected which is the opposite of what you want if simply changing the PPI in this dialog (as outlined in the Change DPI link above).
Another way to think about it is that what they're really asking for is an image sized at 2000 pixels on the long side.
To throw another variable into the mix, depending on which version you are using there will also be options in the Image Size dialog for which algorithm you want PS to use when doing the resample. Bicubic, etc. This link gives a brief overview:
http://help.adobe.com/en_US/Photoshop/11.0/WSfd1234e1c4b69f30ea53e41001031a... |
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