300 dpi, kb file size image for professional printing. Confused!

[Nameless_01]

Hi all,

Im a novice in the design field.

i have an image which is 300 dpi, yet the file size is 420kb. The diemnsions are: 1920 x 1371 pixels. I will be using this image in a professional printed colour A4 (UK) magazine.

Questions:

1 - Will this image be good enough for a full page spread print?

2 - I thought images with 300dpi, also had to be very large in size? - couple of Megabytes surely no?

Please can you educate me in simple terms. Thanks all!

[Willi Adelberger]

The resolution of images is not dpi. Images are meassured in Pixel Per Inch, ppi.

Important is the effective resolution. Your image would have a metric size with 300ppi 18,36 cm width, 11,61 cm height, much smaller than A4. If you have a whole page you have to add bleed in the 3 outer page edges. Your image is to small.

Use a RGB image with a valid color profile, convert with PDF export to the destination profile.

In Photoshop turn on the output cmyk color proof.

[rob day]

The diemnsions are: 1920 x 1371 pixel

Hi @Nameless_01 , The print output width of your image at 300ppi is 6.4 inches (1920/300 = 6.4). If you were to scale it up to 17", its resolution would also scale—the pixels would get larger. The scaled resolution would be 113ppi (1920/17 = 112.9), or the Effective Resolution listed in the Link Info panel

[James Gifford—NitroPress]

I think you have two good answers (but feel free to ask more questions — this can be confusing to novices!) but I want to emphasize something here worth embedding in your modern design knowledge: There is no such thing as a "300dpi (or ppi) image." That value is often emphasized at the file level as if it has meaning, when it does not.

Digital images have only two dimensional factors: their height and width in pixels (1920x1371, in your case) and the height and width at which they are displayed on a screen or printed. The number of pixels per inch (or cm) only becomes relevant when the image is thus presented, and is simply the pixel dimension divided by actual inches. If your image were printed or displayed at 19 inches width, the DPI (usual definition for print) or PPI (usual definition for digital rendering) would be abou 100.

That a "DPI" or "PPI" value can be assigned to a digital image at the file level is merely a minor convenience, and the value is nearly irrelevant. You can open any image file in Photoshop and assign any PPI value you like... and it won't change the image one whit. All that matters is what's sometimes differentiated as the "effective PPI," that of the number of pixels across the display medium. Which InDesign will tell you in the Info panel... and that's useful information.

But there's still no such thing as "a 300dpi image" except in an almost meaningless sense that's gotten stuck in the design vernacular.

[rob day]

The Adobe print applications do assign a print output dimension to an image, which dictates the output resolution.

Photoshop output Width, Height and Resolution (Actual Resolution in InDesign)

InDesign at 100% scale, the image print output dimensions and resolution are the same as in Photoshop:

When the image is scaled, the output resolution changes—the output resolution is listed as Effective Resolution in the Link Info panel.

[James Gifford—NitroPress]

For total clarity, any assigned PPI value is an indication/guideline/suggestion of the nominal 100% final size at that resolution, and yes, most Adobe apps with start from there on import. But that's the end of the value's value, really.

A shop that works to a rigid, consistent layout DPI (magazines, catalogs, etc.) might be correct in saying they work with "300ppi images" but like so many casual references, it's still not technically accurate or rigid.

It's an industry usage that really bugs me because is is so sloppy and deeply misleads in too many ways; I submit the OP as People's Exhibit #1. PE2-12,465 can be found anywhere you find digital design being discussed. ("Oh, use a 300dpi picture and you'll be fine!")

[rob day]

might be correct in saying they work with "300ppi images"

Yes, 300ppi is a rule-of-thumb, and it is useful in that 300ppi is enough resolution to adequately resolve the details in most (but not all) images running on an offset press. Effective Resolution is an important number because it tells you something about the quality of a scaled image relative to the 300ppi rule-of-thumb—113ppi will not be enough resolution to adequately resolve the details in most images.

[Scott Falkner]

1. It depends on the size of the page. At 300 ppi (Pixels Per Inch, not DPI or Dots Per Inch) you image will print at 6.4˝ × 4.6˝. If that is the size of your page then you are gold. If you need it to be larger you will either need a larger image or have to accept lower than 300 pixel per inch output resolution. Scaling the image up will make the pixels larger, making the resolution lower. If enlarged to 11˝ x 8.5˝ the resolution will be 161 pixels per inch.
2. File size is not always a reflection of image quality or image size. Several file formats support compression, which will reduce the size of an . For some images the compression will be great. Uncompressed, your image contains about 7.9 MB of data. If saved as a TIF with LZW or ZIP compression or as PNG the file size will be smaller. How much smaller depends on the type of image. A photograph will not compress much, maybe 50%. A floorplan, logo, simple illustration, or map can much more without any loss in quality. JPEG compression can be dramatic and reduce any image size to a fraction of it's uncompressed size, sometimes with no loss in quality. But JPEG is called “lossy” compression, meaning some data is altered to achieve high compression, which will permanently affect the image.