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Thread: Help : Resizing related

  1. #1
    Punkie
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    Default Help : Resizing related

    Hi peeps. Can someone help me with this thing with resizing? K theres something here i do not understand. Whenever i try to resize my pics in PS6, the pictures resolution shows as only 72 DPI. Most of them actually. Whereas some are 300 DPI. So which is which? When i try to change the value from 72 to 300 dpi, the pic becomes super big. 100+MB. Wah lao.

    Can someone help explain? This is really making me blur.

    Thanks

  2. #2
    qhelix
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    Default Re: Help : Resizing related

    Originally posted by Punkie
    Hi peeps. Can someone help me with this thing with resizing? K theres something here i do not understand. Whenever i try to resize my pics in PS6, the pictures resolution shows as only 72 DPI. Most of them actually. Whereas some are 300 DPI. So which is which? When i try to change the value from 72 to 300 dpi, the pic becomes super big. 100+MB. Wah lao.

    Can someone help explain? This is really making me blur.

    Thanks
    From what I know, the DPI is important when it comes to printing. 300 is the relolution for printing whereas 72 is for web graphics. If your file size is 100mb (that's humongous btw), it could be because you saved in a format other than .jpg

  3. #3
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    Default Re: Help : Resizing related

    Originally posted by Punkie
    When i try to change the value from 72 to 300 dpi, the pic becomes super big. 100+MB.
    ok, without sounding insulting, i think it's easier to explain from the fundamentals. DPI = dots per inch = number of dots used to form one square inch of image in a file. simply put, the higher the DPI of a picture, the finer the 'resolution' and hence the finer the picture.

    now when you increase the DPI value from 72 to 300 without changing the width and height as well, you're actually telling PS to add in more information to the image (aka extrapolation if i not wrong) and hence the file size increase. a simple area calculation - if you change the DPI from 72 to 300, there's actually a 16.5 (roughly lah) times increase in file size...

    hence the explanation for your massive 100+ MB pictures...
    hope that helps you some...

  4. #4
    Punkie
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    Default Re: Re: Help : Resizing related

    Originally posted by firefox13
    ok, without sounding insulting, i think it's easier to explain from the fundamentals. DPI = dots per inch = number of dots used to form one square inch of image in a file. simply put, the higher the DPI of a picture, the finer the 'resolution' and hence the finer the picture.

    now when you increase the DPI value from 72 to 300 without changing the width and height as well, you're actually telling PS to add in more information to the image (aka extrapolation if i not wrong) and hence the file size increase. a simple area calculation - if you change the DPI from 72 to 300, there's actually a 16.5 (roughly lah) times increase in file size...

    hence the explanation for your massive 100+ MB pictures...
    hope that helps you some...
    Hehe thanks for taking the time to explain. Why would i take offence? Should be appreciative others trying to help for the least rite? Anyway I understand perfectly wat you're saying.

    OK let me get this straight. Imagine this scenario. I wanna get one of my photos on a 4R sized print. But its by default 72dpi. How to get my photo to be 300dpi and remain the same sized at the same time? Then if all i gotta do is just change the dpi value to 300 from 72, the image will certainly multiply in size accordingly. The data size of each photo is gonna be so big i think no more than 6-7 images can be burnt onto CD-Rom to send for printing rite?

    Another scenario. I wanna put up this photo on the net. Its a macro shot and i want others to be able to see the finer details. Will 72dpi suffice? And furthermore i need to size it down a little. Probably 1600 x 1200. Wat is the best way to do it?

    This question has probably been asked like a dozen times. And i have also read Darrens Guide to Resizing and Cropping. I do not seem to understand very well wat hes saying(sorry Darren no offence if you're reading this). Its probably my fault for not being able to understand though.

    Mind explaining to me? Coffee? Thanks in advance.

  5. #5
    butters
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    so the bottom line is, should i resize the 1600x1200 pic by default taken from my camera @ 72dpi to 6667x5000 @ 300dpi when i'm sending them in for printing?

  6. #6
    qhelix
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    Well, I myself aren't too familiar with the DPI thing, but normally what I do is just use MS Word, insert the pictures I want and resize them manually. The printouts were quite good, but I dunno whether they're actually considered good or bad. I'm quite sure there should be proper way to do this in order to achieve maximum results.

    Also, people have recommended me using Qimage Pro 2002, which unfortunately is shareware. Apparantly that program does everything for you automatically, all you do is specify how you want the images to be printed out and they will set the proper DPI and other stuff like that. Judging from the comments I've heard, the program is well worth the money if you intend to print lotsa photos.

  7. #7
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    Don't do anything. Send the file in for printing and sleep well.

    This 72dpi vs 300dpi is the most misunderstood thing ever.

    Any DPI number is meaningless when an output size isn't specified. A 1800 x 1200 file @ 300dpi will give a 4x6 print, @ 72 dpi, it will give 25 x 16".

    So there's no need to convert the 72dpi to 300dpi before you send for printing.

    Regards
    CK

  8. #8
    Punkie
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    Originally posted by ckiang
    Don't do anything. Send the file in for printing and sleep well.

    This 72dpi vs 300dpi is the most misunderstood thing ever.

    Any DPI number is meaningless when an output size isn't specified. A 1800 x 1200 file @ 300dpi will give a 4x6 print, @ 72 dpi, it will give 25 x 16".

    So there's no need to convert the 72dpi to 300dpi before you send for printing.

    Regards
    CK
    Oh CK, do you mean just crop it to its print ratio and then send straight for print ah?

  9. #9
    butters
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    but why does the original untouched pic have a 300dpi res(verified by checking its file properties by right-clicking on the image)... & why does photoshop 6 automatically change it everytime to 72dpi whenever the file is edited and saved?

  10. #10
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    Originally posted by butters
    but why does the original untouched pic have a 300dpi res(verified by checking its file properties by right-clicking on the image)... & why does photoshop 6 automatically change it everytime to 72dpi whenever the file is edited and saved?
    Simply because any given image has no inherent output size, only absolute size in terms of pixels. So digital cameras either tag them as 72dpi or 300dpi. This has no relation to image quality of the resultant image. That same 1800 x 1200 image will simply by 4x6" (300dpi) or 25x16" (72dpi) or other combinations (Just divide pixel size by print size (in inches) to get the dpi).

    Punkie - yes, just crop to the ratio and send to the lab. Be careful not to overcrop to too small an image.

    Regards
    CK

  11. #11
    butters
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    Originally posted by ckiang


    Simply because any given image has no inherent output size, only absolute size in terms of pixels. So digital cameras either tag them as 72dpi or 300dpi. This has no relation to image quality of the resultant image. That same 1800 x 1200 image will simply by 4x6" (300dpi) or 25x16" (72dpi) or other combinations (Just divide pixel size by print size (in inches) to get the dpi).

    Punkie - yes, just crop to the ratio and send to the lab. Be careful not to overcrop to too small an image.

    Regards
    CK
    thanks for clearing this up, but there's still a little i dun understand... hope you dun mind me rattling on, but just to clarify..

    so does dpi refer to the pixel density per sq inch? as such, the smaller the print size means the higher the density will become? meaning a 1600x1200 pixel image @ 72dpi becomes 300dpi when printed on a 4x6" paper? sorry for being a little slow, but if the above's correct, then i guess i've more or less grasped the concept...

    thanks ckiang..

  12. #12
    Eric
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    > so does dpi refer to the pixel density per sq inch?

    Yes.


    > as such, the smaller the print size means the higher the density will become?

    Yes.


    > meaning a 1600x1200 pixel image @ 72dpi becomes 300dpi when printed on a 4x6" paper?

    What CK is trying to say is that 1600x1200 is just the resolution (number of pixels) and is not tied to any dpi. The dpi thing only comes in when you want to map the resolution to a certain measurement.

    You are correct in saying 1600x1200 is 300dpi when on 4x6" paper (1200/4=300). 1600x1200 @ 72dpi is roughly 22x16".

    72dpi and 300dpi are just popular values people like to refer to. Computer monitors used to be in the region of 72dpi. Nowadays, they are even higher, depending on the resolution and screen size (my monitor setting is at 97dpi). 300dpi is used by print people for a good quality image.

    When you understand this, there's even more confusing issues like dpi (dots per inch) versus ppi (pixels per inch)

    Hope I helped more than confused.

  13. #13
    butters
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    Originally posted by Eric
    > so does dpi refer to the pixel density per sq inch?

    Yes.


    > as such, the smaller the print size means the higher the density will become?

    Yes.


    > meaning a 1600x1200 pixel image @ 72dpi becomes 300dpi when printed on a 4x6" paper?

    What CK is trying to say is that 1600x1200 is just the resolution (number of pixels) and is not tied to any dpi. The dpi thing only comes in when you want to map the resolution to a certain measurement.

    You are correct in saying 1600x1200 is 300dpi when on 4x6" paper (1200/4=300). 1600x1200 @ 72dpi is roughly 22x16".

    72dpi and 300dpi are just popular values people like to refer to. Computer monitors used to be in the region of 72dpi. Nowadays, they are even higher, depending on the resolution and screen size (my monitor setting is at 97dpi). 300dpi is used by print people for a good quality image.

    When you understand this, there's even more confusing issues like dpi (dots per inch) versus ppi (pixels per inch)

    Hope I helped more than confused.
    u definitely did help confirm my thoughts....

  14. #14
    butters
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    Originally posted by Eric



    > meaning a 1600x1200 pixel image @ 72dpi becomes 300dpi when printed on a 4x6" paper?

    What CK is trying to say is that 1600x1200 is just the resolution (number of pixels) and is not tied to any dpi. The dpi thing only comes in when you want to map the resolution to a certain measurement.

    You are correct in saying 1600x1200 is 300dpi when on 4x6" paper (1200/4=300). 1600x1200 @ 72dpi is roughly 22x16".

    one more question... say u want to print a 1600x1200 pic onto a 22x16" media, but @ 72dpi the print quality would be bad rite? so would increasing it to 300dpi (6667x5000) thru interpolation help improve the print quality?

  15. #15
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    Originally posted by butters


    one more question... say u want to print a 1600x1200 pic onto a 22x16" media, but @ 72dpi the print quality would be bad rite? so would increasing it to 300dpi (6667x5000) thru interpolation help improve the print quality?
    Yes, in that case you would want to do interpolation through a software like Genuine Fractals. There is a limit to how much larger it can interpolate to, and is highly dependent on subject matter and original image quality.

    Regards
    CK

  16. #16
    Eric
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    Originally posted by butters


    one more question... say u want to print a 1600x1200 pic onto a 22x16" media, but @ 72dpi the print quality would be bad rite? so would increasing it to 300dpi (6667x5000) thru interpolation help improve the print quality?
    Not really. Interpolation (or resampling), though better than plain resizing, only can try to make the enlargement smoother, with less pixelation. You can't really "improve" the quality by interpolation, only reduce artifacts from enlargement. Something like diluting a drink by adding water.
    Increasing it to 300 dpi will only create a larger blurrer image.

    Use the dpi value as a guide to how you image may look when printed at a particular size. In your case, the 72dpi is a warning to say that your print quality may not be of highest quality. What you should be thinking about is not whether to increase the pixels through interpolation. You should be considering whether 72dpi @ 22x16 is good enough, or should you maybe go with 11x8.

    I recently did a print at 72dpi (A1 size). Definitely not photo quality, but sometimes, size does matter

  17. #17
    Eric
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    Originally posted by ckiang


    Yes, in that case you would want to do interpolation through a software like Genuine Fractals. There is a limit to how much larger it can interpolate to, and is highly dependent on subject matter and original image quality.

    Regards
    CK
    I haven't heard about Genuine Fractals. Must try it out. Is it better than what the photo labs can do?

    Here is a link to a review at The Luminous Landscape.
    Last edited by Eric; 21st July 2002 at 08:11 AM.

  18. #18

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    Cool, this is really enlightening guys.

    and while we're on this, can i ask a very basic question? say i have taken a pic at resolution 1600x1200, and i wanna send for printing, can i just leave the pic as it is, and tell the shop to print 4R for me?


    and do you bring the cf card to the shop or you transfer to a medium first like cdr or floppy disk, what do they accept?

  19. #19

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    Dear Punkie,

    open your picture in PS6, go to Image

    Image > Image size

    Image size, tick Resample image

    Your pixels will be constent (eg 4Mega pixel 2272 X 1704)

    You could change your dpi from 72 to 300 by highlighting it and type in the new values.

    The size of your print will change.

    As of why your image DPI differs, not sure, my is afixed at 180 dpi

  20. #20
    Punkie
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    Thank you everyone for their kind and enriching responses. Sure did clear up things here. Thanks again peeps. Xie xie...

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