Image Size

I am just in the planning stage for publishing an e-book. I read this recommendation: "Try to keep the resolution on your images between 96 - 150 DPI. You will also want to keep your image size around 500 x 500 pixels or less." I have several RGB images that I want to include that are much larger than this. I experimented with reducing the size in Photoshop Elements. These are all in landscape mode. All of them could be reduced to about 325 X 500 pixels, but the PPI would be 200. Do I need to find a way to reduce that 200 number closer to 150?

Comments

  • My approach, based on experiments and back and forth testing is: 6 inches in width max at 96 dpi.

  • If you're saving them as JPEGs, you can ignore the DPI number. It's irrelevant. JPEGs are only measured by pixels, so if you are offered a pixel x pixel size setting, go with that and your resulting image will be spot on. Test it to be sure by choosing "Info" on the image in your Finder—it'll say how big the final image is in pixels.

     

    Most photo editors offer a DPI density setting because they don't yet know in what format you'll be saving your image. For example, the TIFF format can have more or fewer pixels per inch. JPEGs can't, so that info gets tossed when you save an image as JPEG.

  • Odd, so why do most art/photo applications have a DPI option? I always set the DPI I want regardless of size.

  • First, I goofed to say "DPI," because Dots per Inch is a printer measurement, something designers can't control. I meant Pixels per Inch (PPI). Sorry!

    It's there because some formats use it, such as TIFFs. A TIFF image has a specific size, like 5 x 7, and its pixel density can vary, like 72dpi or 300dpi

    When I see the option, it usually comes before choosing the output format (such as JPEG) or in the same window. So the option might be used.

    A JPEG is always measured in total pixels, like 200x600 pixels. There is no "per inch" or "density." Test it yourself: set a JPEG to 300x500 pixels, and choose 72ppi. Save it. Then do the same at 300ppi. You'll discover that the two images are identical in pixel size and file size. Or, the 300dpi version suddenly has a lot more pixels. It's just bigger.

     

    Learn more in this great article by Lesa Snider.

  • First, I goofed to say "DPI," because Dots per Inch is a printer measurement, something designers can't control.

     

    Well they can as long as they set it to what the printer is capable of. Mine can go up to a ridiculous 19,200 dpi. You have to remember that Lulu use POD that uses bubblejets and lasers, not printing plates. I have no idea what the PR PDFs set the DPI at but they are very sharp and crisp.

    Looking at one of my A5 front covers, it's 3450 x 4950 pixels which is 5.75" x 8.25" @ 600 DPI. Do the maths, but as far as Paintshop Pro 5 is concerned the D = pixels anyway! I could increase or decrease the DPI but it would remain at 5.75" x 8.25".

     


    It's there because some formats use it, such as TIFFs. A TIFF image has a specific size, like 5 x 7, and its pixel density can vary, like 72dpi or 300dpi

     

    It varies depending on what it's been set at. I rarely use less than 300dpi. And do not forget it's also the measurement used my moniters that most of us design on now.

    When I see the option, it usually comes before choosing the output format (such as JPEG) or in the same window. So the option might be used.

     

    Well, in Paintshop Pro New is just one box with all options in including DPI. Default res seems to be 150dpi in it.

    A JPEG is always measured in total pixels, like 200x600 pixels. There is no "per inch" or "density." Test it yourself: set a JPEG to 300x500 pixels, and choose 72ppi. Save it. Then do the same at 300ppi. You'll discover that the two images are identical in pixel size and file size. Or, the 300dpi version suddenly has a lot more pixels. It's just bigger.

     

    Well there is according to the settings in my Paintshop Pro. Image dimensions can be shown (in New) at inches, pixels or centimeters. Next is DPI. If DPI was not important places like Lulu would not recommend any, and I would also recommend that people pay attention to the DPI they set at.

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