Resolution/Quality on 30D?

Discussion in 'Photography Equipment & Products' started by aaronou, Mar 25, 2007.

  1. aaronou

    aaronou TPF Noob!

    Apr 30, 2006
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    norman, oklahoma (blah)
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    Argh!!!!!! I have been taking pictures on my 30D. I am in manual with the RAW+JPEG quality setting.

    The RAW comes out to 240 pixels/inch and the JPEG comes out at 72 per inch! What am I doing wrong? I thought you would at least get 300 pixels per square inch under the image size in PS CS2, at least on the RAW. I promise I am not an idiot, just a technophobe. I know this answer is probably quite simple, but the JPEG is soooo pixellated it is frustrating.

    Please Help! Thanks!

  2. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

    Dec 16, 2003
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    It's an easy answer and one that has been asked many, many times don't feel bad.

    The pixels per inch number doesn't's just a number that determines the size of the image on the computer screen. You could change it to 24 or you could change it to 10,000 (without resampling) and it wouldn't really change the image at all. If the JPEG is pixelated, it's because the zoom level is different.

    What you need to concentrate on is the actual size of the image, in pixels.

    I use the PPI to test/see what size print I could make. For printing, I want 300 PPI, so I set that and it will tell me what the size in inches will be. For viewing on the web, I set the PPI to 72 and reduce the size to less than 800 pixels, which makes for a smaller file.
  3. EOS_JD

    EOS_JD TPF Noob!

    Feb 15, 2007
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    Don't you mean compression? The jpeg compression will determine how "pixelated" the file is. Make sure you have Large fine selected and not a small jpg setting! As Mike says all that matters is the number of pixels.

    Pixels are what images are made of. The resolution coming out of your camera matters not a jot until you come to printing. The only thing that matters is the number of pixels (as has been noted above).

    My 20D (same as your 30D) produces 3504x2336 pixel images. Whether it comes off my camera at 1ppi or 1000ppi the image is still a 3504 x 2336 image. (check the number of pixels of your jpg image).

    Now when it comes to printing there are a couple of very easy ways to work out the unknown variable like print sizes or resolution.

    1. Say you know the size of print you want (eg 10x8) and you want to print it at 300ppi. You would need an image of 3000pixels x 2400 pixels in order to do this. If you have more pixels you can print at a higher resolution or as many do is crop the image to the required pixel count. Quality from printing at higher than 300ppi is unlikely to be seen by the human eye so 300ppi seems to be the preferred quality for small images. You can actually print at around 240ppi without any noticable drop in quality in a small image like this and as noted below you can go a lot lower for large prints.

    2. Say you know the number of pixels you have and you want to print a large 18" x 12" print. At what res will this print out at without resampling the image.

    Resolution= pixels/print size so:
    3504/18 = 194.666 or
    2336/12 = 194.66

    Contrary to popular belief, this will provide a high quality image that will look fantastic from normal viewing distance. Because viewing distance will be further than that of a 6x4, the ppi can be a lot lower for larger images. (look from a distance at a billboard then look close up and you'll see what I mean). By printing these larger images at 300ppi all you do is increase the image size (greatly) and at the normal viewing distance you will not see a difference in the print! I print my 19x13s at just under 180ppi.

    You can also add a third equation to work out how many pixels you need for an image. If you want a 12x8 print at 300ppi you need 12x300=3600 and 8x300= 2400. So you need an image of 3600x2400 (just outside the normal range of an 8Mp camera.

    Now with resampling switched on you can increase the pixel content of your image but because you can print even a 6x4 at around 240ppi without any noticeable drop in quality all you need to do is accept a slightly lower ppi setting.

    I try not to resample too much because all you are doing is either adding information that is not there in the first place (adding pixels or upsampling) or deleting pixel information (downsampling). The only time I do this is if I require a very large print that takes my resolution below around 150ppi.

    Does this make sense?

    Regards the pixelation, as noted above it could be the size of the jpg you are producing or it could be the compression fine I think gives the best quality but lowest compression. Also, make sure you view images at 100%. Any more than this and most images will look pixelated.

    Here's a pretty good link regards resolution.


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