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Old Jul 6, 2003, 6:45 AM   #1
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Default A real 300dpi image

What is proper way to get a digital image at real 300dpi by using any editor (As digital image by any digicam has only 72dpi). Please tell in detail.
thanks!
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Old Jul 6, 2003, 9:10 AM   #2
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Well, with every program the method is different...can't give you the "proper" way unless we know which program you're using.

Most better editing programs have a function called "resize"...choose that and disable "resample" (in PhotoPaint resize is called resample, but by checking "Maintain Original Size" you are just changing the dimensions).

In my example I'm using a 2mp picture that's 1600x1200dpi at 72dpi, or 16.66x22.22 inches...you can then type in/select 300dpi, and most of the numbers should change, it's still 1600x1200 but at 300dpi it becomes a 4x5.33 inch picture.
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Old Jul 11, 2003, 12:08 AM   #3
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Something which has been bugging me is the missleading term dpi. DPI is ONLY a printer term, it means "Dots Per Inch." This is generally far higher than your photo's PPI, or "Pixels Per Inch."

The reason there are two different terms is very simple. Most printers are capable of printing many dots of color per pixel. This creates a much better looking print because it can mix blue and red inks within an individual pixel creating a purlple pixel.

I do hope I can get more people to realize that images are sized in PPI, not DPI. This makes it far less confusing to newbies who go out and buy a 4800dpi printer and try to resize their photos to fit!

I hope I have cleared a little confusion,
Dan O.

PS. Did you know that pixel is an acronym for the two words "Picture Element"?
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Old Jul 11, 2003, 2:22 AM   #4
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I must admit, I've simply never got why dpi is discussed as much in relation to digital photography and why anyone would want to convert the dpi of a digital file.

The numbers only have any relevance when you come to print the image and then only as a rule of thumb as to the likely quality of the output and the biggest size you can expect a good print from - there are many other factors that have more bearing on the visual 'pleasingness' of the finished print.

As a very generalised rule of thumb, an image is likely to look at its best printed out if you have about 300 pixels per inch to print from in the digital file you've selected - that should be about the optimum concentration of detail on the paper. So if you had a digital image 2832 pixels wide you could reasonably expect a really great print at 9.44" wide - or an 8 x 10 print.

But there are far more factors at play in terms of contrast, dynamic range, sharpness, contrast etc. and you can print at very much less digital pixels - per - inch on paper and still get great prints, the image itself has far more impact on how good it looks as it pops out of the printer than any dpi.
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Old Jul 11, 2003, 7:17 AM   #5
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<< an image is likely to look at its best printed out if you have about 300 pixels per inch >>

That is true. Did you also know that if you print at larger than 300ppi your printer may endup creating artifacts in the photo?

300ppi is not the most pleasing resolution. Rather, it is the maximum that most printers offer theses days.

But I agree, you do not need to print at 300 ppi to have a good print. A 150 ppi with a good tonal range, white balance, and such looks just great to the average veiwer.
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Old Jul 11, 2003, 7:37 AM   #6
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Quote:
Originally Posted by Melboz99
That is true. Did you also know that if you print at larger than 300ppi your printer may endup creating artifacts in the photo?
That I would imagine would be down to the individual printer and what it does with interpolation/resampling by itself - software you control youself will almost certainly do a better job if it's necessary.

Quote:
300ppi is not the most pleasing resolution. Rather, it is the maximum that most printers offer theses days.
And as I understand it, the point at which your eye can't perceive any difference if it's a finer resolution - the extra data would be visually wasted, although would come into its own if you wanted to then print bigger from the same image.
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Old Jul 11, 2003, 5:52 PM   #7
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Very intresting but there is a little confusion

When we scan an image there is option to scan at different dpis not ppi, In this case we are not printing jut importing.

Also when we resample an editor ask to enter the value for dpi not ppi

Please also tell a fine quality digital image should have how many ppi.

What is difference between LPI AND PPI
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Old Jul 11, 2003, 7:26 PM   #8
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Quote:
Also when we resample an editor ask to enter the value for dpi not ppi
Yours might, mine does no such thing.

Quote:
Please also tell a fine quality digital image should have how many ppi.
With digital images there is no ppi - just pixels - a digital image is simply specified by its pixel dimensions. A 6MP image is probably around 2832 x 2128 pixels in area (if it's a 4:3 format image) - 2832 pixels wide on the longest length and 2128 on the shortest. If your printer prints out at 300dpi (and you didn't other wise specify the size of the required finished result) - that would give rise to a finished image of 9.44" x 7". If you wanted to print it a lot bigger, the printer would simply stretch out the available pixels to fill the space, possibly degrading the quality accordingly.

So if you printed the same digital 6MP image at 20" x 15", the image would be about 141 pixels of image per inch of paper length when it appeared on the paper, so the quality and detail are likely to be decreased, although on some images, it may not be that noticeable.
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Old Jul 11, 2003, 9:16 PM   #9
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Since most of the relevant information has been covered, let me just add a little about the relative terms and how the final resolution in terms of pixel count is arrived at for the print.

The 72 dpi term comes from the old late 80's MacIntosh computer screens which were the mainstay of the graphics business in the early years. The monitors displayed at 72 pixels per inch and when PhotoShop was in its infancy they simply defaulted to using 72 pixels per inch as a starting point.

The terms PPI (pixels per inch) and DPI (dots per inch) have been used interchangeably for many years even though it's technically incorrect. On the side of common sense, however, a pixel IS a dot to the observer. Many of the professional printers require a file with a density of 300 pixels per inch (often referred to as dpi). This loose usage came about because some of the early printers actually printed one dot per pixel. The early laserjets were 300 dpi devices.

With the development of pico-liter inkjet printers which can lay down numerous tiny dots to represent a single pixel, and thereby mimic continuous tone like you get from a dye sublimation printer, the confusion began.

Any file from any digital camera has no inherent density, just a matrix of numbers derived from the sensor capture. A two megapixel sensor generally produces a matrix of 1600 horizontal by 1200 vertical pixel values. These numeric values have no density until they are either displayed or printed. At that time a decision must be made to display the printed result of these numeric values with some specific concentration which is usually referred to in "ppi" or "dpi" depending on whether we are displaying on a monitor or printing. Professional printers like the Fuji Frontier or LightJet require the information in a format which produces a density somewhere between 300 and 400 dots per inch on the printout. Some pro printers want 300 dpi, some want 400 dpi. The printed result differences are insignificant. As mentioned elsewhere, inkjet prints often look great at much lower densities because each pixel representation in the file is being painted by many tiny dots of ink which overlap.

As mentioned elsewhere, when you divide this native "matrix" from the camera by a figure like 300 (dpi) - you get the size of the printed output in width and height. This figure rarely is exactly the size you want, so depending on the source file size you must either add pixels (interpolation) or remove pixels (resample down) to arrive at a density of 300 pixels per inch (or whatever) to satisfy the printer's requirement.

The more resolution the sensor has, the more pixels there are to represent a given area of geography in the file. Almost any digicam can be used to successfully print poster sized output successfully, but the catch is that with lower resolution captures, you must vastly limit the geography (field of view) in the frame in order to successfully provide good raw data for the interpolation algorithms to do their job or it's GIGO (garbage in, garbage out).

A head and shoulders portrait which represents a very small field of view when captured by a good 3 megapixel sensor like the Canon D30 or Fuji FinePix S1 can be successfully interpolated to produce stunning 60 inch prints. On the other hand, even an 11 megapixel Canon 1DS or a 13.8 megapixel Kodak 14n is insufficient to capture enough data to provide huge prints from an infinity focus landscape with a wide angle lens. One must learn from experimentation what the limits are for their individual equipment. In some cases it's possible to "cheat" a bit by capturing overlapping images and using stitching software to create a single high resolution image from multiple overlapping low resolution captures.

Best regards,

Lin
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Old Jul 12, 2003, 3:43 PM   #10
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Thanks to all for expressing in detail and providing me (newbie) a good deal of information
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