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  • #16
    I moved the off topic section of this thread here:

    http://www.graphicdesignforum.com/fo...ad.php?t=49928
    "Lucy, you got some 'splainin' to do!" - Ricky Ricardo

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    • #17
      Originally posted by decarle View Post
      There are 2 different types of images used by graphic design programs, raster images and vector images.


      RASTER:
      A raster image is made up of thousands of little dots/pixels, photo editors such as Adobe Photoshop are raster based and are great for rendering rich, full colour images like photographs. Raster based programs do have some drawbacks though:

      > Imagine a square 1 inch x 1 inch, if this square has been created at 300dpi then this will have 300 dots/pixels within it. The computer must keep track of all the zeros and ones that make up those 300 dots/pixels, this can result in large file sizes which can be memory intensive when editing, the spec of your PC/MAC will determine if this causes you problems or not.

      > Raster images do not resize well, when you resize a low resolution raster image the pixels just get larger making the image appear distorted and blurry. One solution to this is to ensure the image is created at high resolution, an image at a minimum of 300dpi will resize quite well and keep fairly good clarity, however, it will only enlarge so much.

      VECTOR:
      Vector based programs such as Adobe Illustrator approach image creation in an entirely different way and do not render images on a pixel by pixel basis. Using the same example as above the 1 inch x 1 inch square would only be made up of 4 dots/pixels, one on each corner. These “vector points” allow the computer to play connect the dots, each vector point has information telling the computer how to connect each point with straight or curved lines, and what colour the inner space should be.

      Because the computer only has to keep four points in its memory, it is much easier for the computer to edit vector based images as file sizes are really small. If you resize a vector based image it loses little or no detail, the vector points spread out and the computer just redraws the image. Vector images are ideal for logos as they can be resized and adjusted without losing clarity, so when looking for a logo designer ensure the final files produced are vector based.

      "Imagine a square 1 inch x 1 inch, if this square has been created at 300dpi then this will have 300 dots/pixels within it."

      ???????
      I thought 300 x 300 = 90000

      A square with 300 dots in it = 17.32 dots x 17.32 dots
      @1 inch x 1 inch each dot = 1.46mm x 1.46mm
      Thems mighty big dots

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      • #18
        Hi

        We keep things simple when speaking to student visitors at our studio;

        - pixels for print images & web

        - vector for sharp line graphics that need the ability to be enlarged without loss of quality

        In the real world it's always horrible to be sent a logo from a Client who has grabbed it from the web and they want it on a front cover. In these instances we Google for an Annual Report of literature in PDF format and then import it into Illustrator.

        What would we do without vector for those perfect logos?
        Last edited by garricks; 11-24-2009, 07:34 AM. Reason: Links removed. Advertising is not allowed here.
        Perfection is an addiction.

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        • #19
          Bwahaha!! I looove that movie!! "Youre not my favourite person right now"
          Yes, this comment was random and completely off the topic.

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          • #20
            Originally posted by SeveBallesteros View Post
            "Imagine a square 1 inch x 1 inch, if this square has been created at 300dpi then this will have 300 dots/pixels within it."

            ???????
            I thought 300 x 300 = 90000

            A square with 300 dots in it = 17.32 dots x 17.32 dots
            @1 inch x 1 inch each dot = 1.46mm x 1.46mm
            Thems mighty big dots
            Steve both of these boxes are inch square. One has 72 dpi, the other has 300 dpi.




            "May your hats fly as high as your dreams"Michael Scott

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            • #21
              Originally posted by eugenetyson View Post
              Steve both of these boxes are inch square. One has 72 dpi, the other has 300 dpi.



              I do understand the resolution thing, but really that wasn't my point.
              The point I was making was that decarle posted "within it" when referring to a 1 inch x 1 inch square @ 300dpi. Okay, there is 300 dots along a 1 inch line, but not "within" a 1 inch square, that would be 90000 dots. Likewise a 1 inch square @ 72dpi, doesn't have 72 dots "within it", but rather 504 dots, "within it". When quoting dpi I think area doesn't need to be mentioned at all, since dpi isn't a two dimensional value, but simply the resolution of a linear quantity. I suppose if pixels were rectangular and not square, then that's another story.

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              • #22
                Gotcha, it should read:
                1 x 1 inch square @ 300 dpi has 300 dots per inch.

                Not:
                1 x 1 inch square @ 300 dpi has 300 dots/pixels within it.

                Well technically it's true, it's just doesn't give the total number of pixels


                I think what they were getting at is that if you had an image that was:

                1600 x 900 pixels. Then at print size @ 300 dpi it would be 5.3 inches x 3 inches, for example.

                "May your hats fly as high as your dreams"Michael Scott

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                • #23
                  Originally posted by eugenetyson View Post
                  Gotcha, it should read:
                  1 x 1 inch square @ 300 dpi has 300 dots per inch.

                  Not:
                  1 x 1 inch square @ 300 dpi has 300 dots/pixels within it.

                  Well technically it's true, it's just doesn't give the total number of pixels


                  I think what they were getting at is that if you had an image that was:

                  1600 x 900 pixels. Then at print size @ 300 dpi it would be 5.3 inches x 3 inches, for example.
                  Sorry to labour this, but I might as well finish the point I was making, i.e. that technically it's not true, rather than just making no comment to your last post.

                  The technical true statement is in my mind, a 1 inch x 1 inch square @300dpi contains 300 pixels along its horizontal edge, and 300 pixels along its vertical edge, which equates to an array of 90000 pixels in total.

                  But such a statement is really a tautology. It's like saying, 1 mile, with 5280 feet per mile, has 5280 feet within it.

                  I can understand how someone might say an image with one edge measuring 3.25 inches @ 300dpi equates to 975 pixels along that 3.25 inch edge.

                  Sorry. Just had to get that out of my system.

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                  • #24
                    It's all web pixels versus print pixels to me.

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                    • #25
                      Originally posted by eugenetyson View Post
                      Steve both of these boxes are inch square. One has 72 dpi, the other has 300 dpi.



                      I understand this right, but does inches then have any relevance at all? Because (oops never start a sentence with because) that second image is clearly not 1" x 1". I have loads of problems with this in photoshop. I'm cropping to a certain size say 4" x 6" but when I print it out it's tiny. I frequently just place it in a word document to make it the right size. I'm not sure how else to do it, or to avoid the sizes being wrong.
                      My portfolio.

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                      • #26
                        From what you are saying, I guess you mostly use your images in low resolution. Use pixel measurement to determine the size of the image at 72 pixel/inch resolution. For PowerPoint usage, use 96.

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                        • #27
                          Originally posted by lucdesaulniers View Post
                          From what you are saying, I guess you mostly use your images in low resolution. Use pixel measurement to determine the size of the image at 72 pixel/inch resolution. For PowerPoint usage, use 96.
                          SO what you're saying is divide pixel height by resolution amount and that should show the actual height in inches?
                          My portfolio.

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                          • #28
                            Yes take one image

                            If you have 900 x 600 pixels and the resolution is 300 ppi

                            Then it's 3 inches x 2 inches

                            If you have 900 x 600 pixels and the resolution is 72 ppi
                            Then it's 12.5 inches x 8.33 inches


                            It's effectively proportional

                            "May your hats fly as high as your dreams"Michael Scott

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                            • #29
                              So, should I always work in pixels then instead of mm? Is there a way to get photoshop to show the actual size physical dimensions should it be printed out?
                              My portfolio.

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                              • #30
                                Let me start by saying I know this isn't definitive, I apologise for any mistakes or omissions.

                                And I know it's scary stuff and a lot to take it in. I used to be very intimidated by all of this too. But once you get your head around how it's calculated you better understand how it all works together - well I do anyway.


                                Working in ppi or pixels or inches or mm is just a conversion of units. Work in whatever makes you comfortable and you understand.

                                Personally I work in mm for printing and Pixels for Web

                                For a 72 pixels per inch image

                                If 72 pixels = 1 inch - so 900 pixels = 12.5 inches

                                72 pixels = 2.54 cm - so 900 pixels = 31.75 cm

                                72 pixels = 25.4 mm so 900 pixels = 317.5 mm

                                72 pixels = 0.0149254731 smoots so 900 pixels = 0.18... smoots


                                For a 300 ppi (pixels per inch) image

                                300 pixels = 1 inch

                                300 pixels = 2.54 cm

                                and so on



                                For images going on the web I work in Pixels

                                For images for print I work in MM

                                ____________________________________
                                If your image is 72 pixels per inch and you need it for print you have two options to get to 300 pixels per inch.

                                Option 1
                                You can increase the amount of pixels per inch, which means the print size gets smaller.

                                So a 900 x 600 pixel image

                                @72 ppi is 12.5 inches x 8.3 inches
                                @300 ppi it's 3 inches x 2 inches (76.2mm x 50.8mm)

                                _________________________________________________

                                Option 2
                                Or you can add more pixels to the image (called upsampling) which in effect increase the amount of pixels but keeps the dimensions (12.5 x 8.3)

                                So if you have 900 x 600 @ 72 ppi and want to make it 300 ppi you add more pixels to the image in this case you know that the image is 12.5 inches x 8.3 inches

                                So you need fill each inch with 300 pixels, so it's 300 pixels per inch.

                                You can do this by increasing the percentage size of the image, here you're dealing two figures 72 and 300

                                (300/72)*100 will give you the percentage you need to increase the image by

                                which is 416%.


                                So you increase the image 416% to bring it from 72 to 300. But as I said this is called Upsampling. Which uses an interpolation to fill in the pixels.

                                __________________________________________________ ____________

                                Interpolation

                                These pixels are approximated from surrouding pixels.

                                So if there's 1 pure black pixel surround on all sides by other pixels that are 50% - and you increase the image by 416%, then there are less pixels per inch and the software attempts to fill in the missing pixels with an approximation of pixels ranging from 50% to 100% in fill value per pixel (based on the amount you've increased by).



                                Upsampling is not deisreable as the software does a very washy job of interpolating the pixles. It's best not to upsample images past 120% after this the difference is very noticeable.
                                Last edited by hank_scorpio; 01-24-2010, 09:40 AM.

                                "May your hats fly as high as your dreams"Michael Scott

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