The result was four images for each patient consisting of the original uncompressed images and three compression ratios, adding up to 76 images.Įxample of images of a patient in (a) DICOM, (b) JPEG2000 85, (c) JPEG2000 75, (d) JPEG2000 60 formats
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The compression ratio expresses the difference between the file size of the original image and the file size of the same image when compressed.
How to compress picture files for storage software#
Three JPEG2000 compressed image groups were created by using this software at quality factors of 85, 75, and 60. Photoshop uses a quality-factor scale that ranges from one (lowest quality) to 100 (highest quality) for JPEG2000 compression. In the second stage of the study, digital images were compressed using an Adobe Photoshop CS5 version 12 software (Adobe Systems, San Jose, Calif). The images were saved in DICOM format, each with a file size of 9.649 MB. To standardize the radiographic technique, the lateral cephalograms were obtained by a single technician. The patients were placed in a natural head position, looking at their eyes reflected on a mirror positioned in front of the patient. All radiographic images were acquired with a Soredex (Cranex D, Finland) radiographic machine with an exposure time of 9.1-14.6 s, set at 73-81 kVp and 10 mA, on a charge-coupled device (CCD) sensor (Cranex D, Finland). In this analytical-descriptive study, 19 direct digital lateral cephalograms that had been acquired for routine orthodontic treatment were used. Thus, this study evaluated whether JPEG2000 quality factors 85, 75, and 60 altered the image quality compared with the DICOM image enough to influence the identification of cephalometric points on direct digital lateral cephalogram images. The studies on cephalometrics have emphasized that more research in this field with adequate methodology is necessary. Many investigations have been conducted to evaluate the compression ratio that may be used without loss of accuracy for different diagnostic purposes in dentistry, for example Noujeim et al., evaluated the effect of JPEG compressions on the diagnostic capability of periapical images in the detection of root fractures, the compression reduced the file size considerably, but it did not affect the accuracy of root fracture detection. Orthodontists, radiologists, and maxillofacial surgeons frequently use cephalometric measurements obtained on JPEG cephalogram images. It also offers progressive image reconstruction, provides more options and greater flexibility than the standard JPEG format. Compared with JPEG, JPEG2000 allows higher compression without compromising quality. This file format has been adopted by the digital imaging and communication in medicine (DICOM) standard. The JPEG2000 file format was developed to address some deficiencies in the original JPEG standard. The most common file format that offers lossy compression is the joint photographic experts group (JPEG) format. Lossy compression, on the other hand, although offering considerably higher compression ratios and smaller file sizes, involves irreversible loss of data that could be essential. However, the approximate compression ratio is 1:2-1:4, depending on image characteristics. Lossless image compression methods preserve all image information and their use is not questioned.
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Lossless compression eliminates nonessential information in the image while conserving essential data so that the digital image can be reconstructed exactly. There are two methods of image compression: Lossless and lossy.
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Compressed images need less storage space and decrease the transmission time, since the compressed file is smaller because of the reduced amount of binary data used to represent the image. One method to overcome this transmission overload is to compress the image files. With increase of digital imaging, the need for storage space and transmission speed also increases. The development of cost-effective extraoral digital technology, coupled with increased use of computers in orthodontic practice, has made direct digital cephalometric imaging a valid opportunity.