![]() ![]() Upper row: can you spot the difference? Click the image to see full size. In all the other situations keep it the same as the scanner. The main point is that when converting to a binary image (only two possible color) or to a very small color palette (e.g. However you can scan at any higher densities but this will be reflected in the file size and processing/displaying time on computer. The result will be a 300 DPI image with indexed color (custom palette).ģ00 DPI is a density that usually works for all kind of pages. The next step is to determine approximately how many colors are really used on the image. This mode usually means 24-bit color, a total of 256 3 = 16.7 millions of possible colors. Color page: of course you will scan this in color mode.The result will be a 300 DPI grayscale image. This is the selected option also when you can't see any dots on the picture (it was printed in real grayscale mode). I wouldn't recommend this unless you really need to use a higher DPI for the text. The page was printed at a higher DPI than the one you scanned at.Do you still see dots? If yes, then you can process it at 600 DPI monochrome. Zoom the raw image you scanned (try at 300 DPI). If you see dots, then the picture is in 1-bit monochrome. Take a close look at the printed paper or use a magnifying glass and look for visible dots. But the pictures matter here because you must figure what their color depth really is in order to make a correct software processing. Black and white page with text and pictures: you will scan this in grayscale mode.After processing the image will be 600 DPI indexed color with a limited color palette (the software I'll use doesn't allow less than 4 colors). If the text is any other color than black do a 300 DPI color scan. After software processing the result will be a 600 DPI binary image (1-bit monochrome, bitmap). Simple page with text: if the text is black do a 300 DPI grayscale scan.The third offered mode (bitmap, 1-bit, binary) is actually a grayscale scan that is converted by the software to bitmap. Scanners only have two modes: full color and grayscale. There's nothing wrong with pixel resolution and it should never be lowered because the reported size is way too much than physical size.īefore scanning a page you should correctly determine its color depth. Imagine a 500 pages book.ĭPI is the only parameter that should be corrected when using a photo camera to scan. If this is scanned at full color (3 bytes per pixel) and no compression is applied, the resulting file will have a size of 2481 x 3507 x 3 / 1024 / 1024 = 24.89 MB. Thus the resulting scanned image will have a resolution of 8.27 x 300 = 2481 px width by 11.69 x 300 = 3507 px height. Let's assume you scan an A4 sheet at 300 DPI. You can't change the physical size of the paper. Resolution divided by DPI equals the physical size of the image in inches. These parameters are contained in the image metadata so as long as DPI * size remains constant, no pixel is changed in the actual image. It is highly related to DPI (dots per inch) value. Size refers to the physical size of the image. A color image using 24 bit color definition takes 3 bytes for every pixel (the color of a pixel is defined by three values: red, green and blue which can have any value between 0 and 255 - that's one byte). It is very important as it determines the amount of 'data' the image contains. Resolution, DPI and size Resolution actually refers to image width and height in pixels. But let's start with the basics.Īvoid/skip any processing done by the scanning software or by the photo camera. All software used in this tutorial is free (some apps are open-source). Yet, if the image from scanner has a low resolution, further processing is useless and may have negative results. Software processing of the raw image from scanner plays a very important role. A high quality scan must preserve as much detail as possible, must have the correct page size (when printed at 100%, the resulting copy should be exactly the same size as the original), must load as quick as possible on low-end devices and shouldn't eat the whole drive space. A low quality scan is hard to read (impossible to run OCR). Nothing will be lost during the conversion as lossless compression will be used and OCR will be run on documents. ![]() This post will not talk about scanning only, but about the whole process of turning a sheet of paper, a magazine or a book into a high quality digital document of the smallest possible size. Learn what resolution, DPI and color depth mean. How to get the smallest file size without losing quality. ![]()
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