A print shop/graphics designer/magazine asks a client for a photo at 300 dpi. They wish to print it out 7" x 5". The client already has a beautiful digital photo with pixel dimension of 2048 x 1536. The client notices that the photo editing software is showing that the photo is set to 72 dpi. So, following orders, the client types in 300 to reset the dpi to 300. In doing so the image is resampled and is enlarged over 4 times to pixel dimensions of 8533 x 6400. The client sends this enlarged 300 dpi photo. The print shop/graphics designer/magazine rejects it (too grainy, too colour blotched). The client is crushed.
The sad thing is that the client already had the perfect photo (2048 x 1536 @ 72 dpi) which would have been beautifully printed at 7" x 5" ( at 292.6 PPI). The print shop / graphics designer /magazine didn't know what they really wanted. - READ WHAT PRINT SHOP REALLY WANT and the client didn't know how to change the DPI without resizing the image to give the print shop what they mistakenly think they need .
Solutions.
To solve this problem, first, you must understand the meaning of DPI, PPI and resample image.
What is DPI and PPI?
DPI (dots per inch) is a measurement of printer resolution, though it is commonly applied, somewhat inappropriately, to monitors, scanners and even digital cameras.
For printers, the DPI specification indicates the number of dots per inch that the printer is capable of achieving to form text or graphics on the printed page. The higher the DPI, the more refined the text or image will appear.
In the case of monitors, DPI refers to the number of pixels present per inch of display screen. The technically correct term is "PPI" or pixels per inch, but DPI is commonly used instead. A display setting of 1280 x 1024 has 1.3 million pixels on the screen, while a setting of 800 x 600 has 480,000, or less than half the resolution of the higher setting. With fewer pixels, the picture will not have the clarity that can be achieved with a higher saturation. Each dot or pixel reflects a certain color and brightness. The greater the number of pixels, the more detailed the picture can be.
Resizing and resampling images.
When you resize an image and resample it, you change the amount of data in that image.To resample your image, ensure Resample Image is checked at the bottom of the Image Size dialog box. Resample is on by default.
Resampling changes the total n umber of pixels in the image, which are displayed as Width and Height in pixels in the Image Size dialog box in the Pixel Dimensions section. When you increase the number of pixels in this section of the dialog box (upsampling), the application adds data to the image, and when you decrease the number of pixels (downsampling), the application removes data. Whenever data is removed from or added to the image, the image quality degrades to some extent. Removal of data from an image is usually preferable to the addition of data, because upsamping requires that Photoshop or Photoshop Elements guess which pixels to add; this is a more complex procedure than guessing which pixels to remove, when you downsample. You will get the best results working with images that you bring into Photoshop in the proper resolution for the output you want. You may get the results you need by resizing your image without resampling. However, if you need to resample your images, you'll want to do so only once.
When you check, or turn on, Resample, you can change any or all of the three values in the Image Size dialog box: pixel dimensions, physical size, or resolution. If you change one value, then you will effect the others; the pixel dimensions are always affected.
- If you change the pixel dimensions, then you will affect the physical size, but not the resolution.
- If you change the resolution, then you will affect the pixel dimensions, but not the physical size.
- If you change the physical size, then you will change the pixel dimensions, but not the resolution.
REMEMBER!
You cannot set the file size; it changes when you change the total amount of data in the image (the pixel dimensions). If you note the file size value before you change the other values in the dialog box, then you can use the file size information to understand how much data will be removed or added to your image when you resample the image. For example, if the file size changes from 250 KB to 500 KB, you'll be adding twice as much data to the image, which may seriously degrade the image. Degraded images may look blurry, or jagged or blocky.
Image sizes on the screen and in print
The size of an image when you view it on the screen is different from the size of an image when you print it. If you understand these differences, then you can develop a better understanding of which settings to change when you resize an image.
Screen size
The screen resolution of your monitor is the number of pixels that your monitor can display. For example, a monitor with a screen resolution of 640x480 pixels will display 640 pixels for the width and 480 pixels for the height. There are several different screen resolutions you can use, and the physical size of the monitor screen usually determines the resolutions available. For example, large monitors typically display higher resolutions than small monitors because they have more pixels.
To find out what your screen resolution is, choose Start > Control Panel > Display > Settings and look at the screen resolution (Windows) or System Preferences > Displays and look in the resolution section (Mac OS).
Image size on the screen
Images are of a fixed pixel size when they appear on your monitor. Your screen resolution determines how large the image appears to be. A monitor set to 640x480 pixels displays fewer pixels than a monitor displaying 1024x768 pixels, so each of the pixels on the 640x480 pixel monitor will be larger than each of the pixels displayed on the 1024x768 pixel monitor.
An image of 100x100 pixels will take up approximately 1/6 of the screen at 640x480, but it will only take up approximately 1/10 of the screen at 1024x768, so the image will look smaller at 1024x768 pixels than at 640x480 pixels.
Image size in print
The other values used in resizing images, the physical size of the image when printed, and the resolution (the number of pixels per inch), aren't used in calculations until the image is printed. When you go to print, the physical size of the image, the resolution, and the pixel dimensions interact to determine the amount of data in the image and its print quality. In general, higher resolution images print at a higher quality.
Conclusion :
First, The print shop must know about dpi and ppi because DPI is nothing to do with digital image resolution or quality. If the print shop said they cannot print the image because of dpi, we can explain to them what is the differences between dpi and dpi. Remember, to get the better image quality , do not resample the image, just increase theDPI.
Another thing, 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.
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