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DPI And Photos

What Print Shops Truly Mean by DPI: When a print shop, graphics designer, or magazine requests a digital photo at 300 DPI, they are essentially asking for an image that can be printed at a specific paper size in inches with a resolution of 300 pixels per inch (PPI).

It’s important to note that the term DPI, although commonly used, is often mistaken for PPI and no longer accurately reflects the paper output quality or resolution of a printed image in terms of printer dots per inch.

Photo set to 1000 dpi Photo set to 10 dpi

Can you tell the difference ?? Answer : No you can’t, because there is no difference

In the context of a print shop, if they require a digital photo to be printed at dimensions of 10 inches by 8 inches with a resolution of 300 PPI, what they truly need is an image with pixel dimensions of 3000 pixels by 2400 pixels (regardless of the DPI setting of the image).

The Actual Requirements of Print Shops: It’s worth mentioning that the notion that 300 PPI equals photographic quality is based on outdated printing equipment from a decade ago. Nowadays, modern printers can produce a good quality digital photo with “photographic quality” at 200 PPI. Consequently, the specifications for a 10 inch by 8 inch paper photo would translate to a good quality digital image with pixel dimensions of 2000 pixels by 1600 pixels.

To achieve a high-quality digital photo, the following factors are important:

  1. Capture the photo using a high-quality digital camera with excellent optics and a good digital sensor.
  2. Avoid any form of enlargement during post-processing or by using digital zoom in the camera (digital zoom should never be used).
  3. Ensure that the photo is properly taken, with adequate lighting and no blurring.
  4. Capture the photo within the camera’s optimal ISO range, typically a low ISO such as ISO 100.
  5. Store the photo in a lossless format like TIF or a minimally compressed JPEG file (using the highest camera JPEG quality setting).

Such a photo will reproduce on paper at photographic quality (assuming current printing technology) at 200 PPI.

A Note to Print Shops and Graphics Designers: I keep getting emails from poor folk who say that their print shop or graphics designer keep asking for digital phots at “number of” DPI (usually 300 DPI). Please STOP DOING THIS to your poor clients – ask for what you really need, pixels in your prefered format (i.e. low compressed JPG or a TIF). If your need is for a digital photo that can be printed at high quality at a width of 6 inches, and you think that 300 ppi is what is required to do this (based on your equipment), then you need a digital photo that is 1800 pixels in width (regardless of its DPI setting since it’s a meaningless figure).

So, ask for a digital photo that is at least 1800 pixels in width. Tell your client not to resize the photo. If the photo is less 1800 pixels, ask them to send it along anyway (so that you can test it) and that if it is larger than 1800 pixels it’s also okay (don’t have them resize a larger photo down to your “at least” pixel figure). If you are running older equipment/software that needs a particular DPI setting, then set it in the photo after you have received it.

Also, please don’t ask for a digital image of  0000 Kb in file size (I’ve had print shops do this). This is even more meaningless than the DPI figure since the file size depends not only on the format (JPEG, TIF) but the compression used with that format. If you are in a long term relationship with the client, educate the client to take photos at the highest quality setting their digital camera allows (and then ask for a copy of the original photo) or if they are scanning (where DPI does count in converting paper inches to digital pixels), specify the resulting pixel dimensions that you want.

There are four main factors that determine image quality:

  • 1) The quality of the recording device (camera’s optics and sensor, scanner’s sensor).
  • 2) The size (in pixels) of the digital image.
  • 3) The digital format it is stored in (lossless vs lossy compression).
  • 4) The technical proficiency and the “eye” of the photographer.

By adhering to these guidelines, a photo can be reproduced on paper with photographic quality (given current printing technology) at 200 PPI.

The resolution of a digital photo is measured in pixels, which represent the smallest color components in the image. In the example provided, both photos have the same dimensions of 300 pixels in width by 225 pixels in height, and they have been saved with 25% JPEG compression. Despite having different DPI values, the quality of the photos remains identical since the pixels themselves do not change.

This raises the question: What is DPI, and why do many people place so much emphasis on it?

DPI stands for “dots per inch” and is a measure of how an image is printed or scanned on a medium such as paper. Unfortunately, the term DPI is often misunderstood because some software programs inaccurately refer to it as “resolution,” which further adds to the confusion. DPI actually refers to the resolution of the printed output and has no direct relationship with the resolution of the digital image.

In fact, software programs that use DPI settings typically do so because they lack WYSIWYG (what you see is what you get) output capabilities. In contrast, WYSIWYG software like word processors, desktop publishing tools, photo printing programs, and graphics software such as Adobe Illustrator or Corel Draw do not rely on DPI as a meaningful figure. Instead, the output quality is determined by factors such as the pixel size of the original image, the chosen paper dimensions for printing, and the printer’s quality.

However, some older photo programs still rely on DPI as a means to determine the size of the output on paper. In the provided example, the photo set at 1000 DPI would print out at a width of 0.3 inches (300 pixels divided by 1000 dots per inch = 0.3 inches) in a non-WYSIWYG program. On the other hand, the same photo set at 10 DPI would print out at a width of 30 inches.

Therefore, it becomes clear that DPI is primarily used to set the size of the printed output in certain photo programs. If one wishes to print a photo with a width of 5 inches using a program that relies on DPI for setting the dimensions, they would need to set the DPI to 60 (300 pixels / 60 DPI = 5 inches). However, if the same photo is imported into programs like Word, Corel Draw, or Adobe Illustrator, the DPI becomes irrelevant. Simply resizing the image to a width of 5 inches would yield an identical print result, regardless of the photo’s DPI setting.

Most digital cameras’ accompanying photo software allows users to specify the desired output size (e.g., 4″ x 6″, 5″ x 7″) and automatically prints the photo at that size. It is worth noting that the internal DPI of most digital camera photos is typically 72, although we now understand that DPI does not directly affect the digital image quality.

DPI vs PPI: Technically, DPI refers to the number of dots per inch that a printer can produce on paper, while PPI refers to the number of pixels per inch in a digital image. However, in practice, the term DPI is often used incorrectly when PPI is actually what is being referred to. Even in these articles, there is some overlap of terms because many software programs still use the outdated term DPI to mean PPI. Therefore, it’s important to consider the context in which the terms are used.

When someone mentions DPI, are they really discussing the printer’s dots per inch, or are they actually referring to the number of pixels per inch at which a digital photo will be printed? This is where many print shops, graphic artists, and magazines make a mistake when they talk about the required resolution of a digital photo. They erroneously believe that the DPI setting in a photo has something to do with it, when in reality, what they need is a specific PPI value.

Some programs, like Adobe Photoshop, now refer to what used to be called DPI as “pixels/inch” or “pixels/cm.” While this is a step in the right direction, it can still be confusing because these settings are often found under a section called “Resolution,” leading people to mistakenly think that they relate to the digital resolution of the photo. Some camera manufacturers, such as Canon, use the correct terminology by referring to the digital resolution as the pixel dimensions of the photo.

To clarify, neither the DPI nor the PPI setting in a digital photo alters its digital quality. The resolution of a digital photo is determined by its pixel dimensions.

The Disastrous DPI Misunderstanding: Let’s imagine this scenario – a client receives a request from a print shop, graphics designer, or magazine to provide a photo at 300 dpi for printing it at 5″ x 7″. The client already possesses a stunning digital photo with pixel dimensions of 2048 x 1536. Upon inspecting the photo using editing software, they notice that the dpi setting is displayed as 72. In order to comply with the request, the client obediently changes the dpi to 300. Unfortunately, this action triggers image resampling, enlarging the photo to pixel dimensions of 8533 x 6400, over four times its original size.

The client then sends this enlarged 300 dpi photo to the print shop, graphics designer, or magazine. However, it gets rejected due to excessive graininess and color distortion. The client is left devastated. The unfortunate truth is that the client initially possessed the perfect photo (2048 x 1536 @ 72 dpi) that would have been beautifully printed at 5″ x 7″ (at 292.6 pixels per inch). The problem arose because the print shop, graphics designer, or magazine didn’t truly understand what they needed, and the client lacked the knowledge of how to adjust the dpi without resizing the image, consequently providing what the print shop mistakenly believed they required.

So, why is DPI important? Well, if you’re using an older photo program, it may rely on DPI to determine the size of the printed output. In such programs, adjusting the DPI becomes necessary to modify the printed size. However, this practice is becoming less prevalent as most modern photo programs allow you to simply specify the desired output size (e.g., 5″ x 7″) for the image, irrespective of the dpi setting.

In reality, programs that use DPI to set the size of printed output are essentially utilizing PPI (pixels per inch). They are not instructing the printer on how many dots per inch to print (DPI), but rather providing the printer with a certain number of pixels per inch (which the printer may even print at a higher DPI).

Certain programs, such as word processors and desktop publishing software, may use the dpi of an image to establish the default size of the image. For instance, a 1200-pixel-wide image set to 200 dpi would load into such a program at a size of 6 inches. Although modern programs allow easy visual resizing of such images, it can be convenient to set the dpi of images intended for use in these programs to match the approximate paper size.

For example, if you have a 2400-pixel image to be included in a document at 3 inches in width, setting the dpi to 800 would be appropriate. However, it is crucial to always set the dpi without resampling the image, as resizing the image may negatively impact its quality.

The Importance of DPI in Scanning: Scanning involves the conversion of paper documents or photos into digital format, and DPI plays a significant role in determining the level of detail in the resulting scan. The DPI setting of the scanner directly affects the pixel dimensions of the scanned image. For example, if a 5″ x 7″ photo is placed on the scanner and scanned at 300 DPI, the resulting digital image will have dimensions of 1500 x 2100 pixels (5″ x 300 = 1500 and 7″ x 300 = 2100).

In this case, DPI does indeed impact the quality because a higher scanner DPI setting captures more information during the scanning process. However, it’s important to remember the concept that 200 PPI (pixels per inch) generally corresponds to photo quality, so a minimum of 200 DPI is recommended when scanning. For paper photos, optimal results are typically achieved within the range of 300 DPI (sufficient for most photos) to 600 DPI (if the intention is to enlarge the image).

A Cautionary Note: It’s crucial to be cautious when changing the DPI of a photo, as some programs may inadvertently resize the image (as demonstrated in “The Horrible DPI Mistake” example). To adjust the DPI without altering the pixel size of the photo, it’s advisable to select options like “maintain original size” (available in programs such as Adobe Photoshop, Corel PhotoPaint) or disable the “resample image” feature. By using these settings, the DPI can be modified without unintentionally resizing the image.

Still want to change the DPI Size in your photos, read this: How to change the DPI in your Photos.

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