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 . with increase of digital imaging , the need for storage space and transmission speed also increases . 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 . lossless compression eliminates nonessential information in the image while conserving essential data so that the digital image can be reconstructed exactly . lossless image compression methods preserve all image information and their use is not questioned . however , the approximate compression ratio is 1:2 - 1:4 , depending on image characteristics . 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 . the most common file format that offers lossy compression is the joint photographic experts group ( jpeg ) format . the jpeg2000 file format was developed to address some deficiencies in the original jpeg standard . this file format has been adopted by the digital imaging and communication in medicine ( dicom ) standard . it also offers progressive image reconstruction , provides more options and greater flexibility than the standard jpeg format . orthodontists , radiologists , and maxillofacial surgeons frequently use cephalometric measurements obtained on jpeg cephalogram images . 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 [ from 1.77 megabytes ( mb ) to 453 and 95 kilobytes ( kb ) ] , but it did not affect the accuracy of root fracture detection . the studies on cephalometrics have emphasized that more research in this field with adequate methodology is necessary . 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 . in this analytical - descriptive study , 19 direct digital lateral cephalograms that had been acquired for routine orthodontic treatment were used . 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 ) . the patients were placed in a natural head position , looking at their eyes reflected on a mirror positioned in front of the patient . to standardize the radiographic technique , the images were saved in dicom format , each with a file size of 9.649 mb . in the second stage of the study , digital images were compressed using an adobe photoshop cs5 version 12 software ( adobe systems , san jose , calif ) . photoshop uses a quality - factor scale that ranges from one ( lowest quality ) to 100 ( highest quality ) for jpeg2000 compression . three jpeg2000 compressed image groups were created by using this software at quality factors of 85 , 75 , and 60 . this resulted in compression ratios of 11:3 - 15:7 , 17:1 - 26:7 , 39:5 - 73:1 , respectively [ figure 1 ] . the compression ratio expresses the difference between the file size of the original image and the file size of the same image when compressed . the result was four images for each patient consisting of the original uncompressed images and three compression ratios , adding up to 76 images . ( b ) jpeg2000 85 , ( c ) jpeg2000 75 , ( d ) jpeg2000 60 formats to avoid bias , an independent investigator copied the images to another folder for sample blinding , numbering the image files from one to 76 and keeping the original folder . therefore , when the examiner identified the cephalometric landmarks on the images , he was not aware of their quality factors . the cephalometric points were identified by a professional on an hp probook 4520s computer with an intel core i3 cpu m 370 @ 2.4 ghz , 3.00 gigabyte ( gb ) ram and a 14-inch screen with resolution 1366  768 ( china ) . the examiner was not allowed to change the brightness and contrast of images or to use the zoom tool . the cephalometric landmarks were identified using a location tool based on the x - y coordinate system ( horizontal and vertical axes , respectively ) . the horizontal and vertical locations of each point were measured in pixels ( 120 pixel = 1 cm ) . the following cephalometric points were identified : ans anterior nasal spine ( the tip of anterior nasal spine ) b b - point ( the deepest point in the concavity of anterior border of the mandible ) a a - point ( the deepest point of the anterior border of maxillary alveolar ridge concavity ) or orbitale ( the most inferior point of the infra orbital rim ) s sella ( centre of hypophyseal fossa ) pog pogonion ( the most anterior point of the symphysis ) ui incisal ( incisal edge of maxillary central incisor ) n nasion ( the anterior point of the intersection between the nasal and frontal bones ) to evaluate the method error , the cephalometric points were once again identified by the examiner after 1 month interval . for evaluation of intra - examiner error , the reproducibility in the identification of points , i.e. to determine if the point was identified on the same coordinate or close to it , was evaluated by analysis of variance ( anova ) . comparison was performed between data collected from images with quality factors 85 , 75 , and 60 and the dicom images . anova was applied to investigate if there was a statistically significant difference in the location of cephalometric points between each group of images . the correlation coefficient between the cephalometric points identified at repeated sessions was 0.99 , revealing that the identification of cephalometric points is highly reproducible . the mean and standard deviation ( in pixels ) of the location of the points in the original dicom image and that of each compressed images are presented for each landmark on the x and y axes in tables 1 and 2 . meansd ( in pixels ) of the original dicom and each quality factor ( qf ) for the x coordinate meansd ( in pixels ) of the original dicom and each quality factor ( qf ) for the y coordinate table 3 demonstrates that the different file formats , on average , were statistically similar for each point and axis ( p > 0.05 ) . the results did not demonstrate any statistically significant difference in the identification of the eight cephalometric points between the dicom images and the jpeg 2000 quality factors 85 , 75 , and 60 . results of analysis of variance ( anova ) , comparing each image group ( dicom , jpeg2000 85 , jpeg2000 75 , and jpeg2000 60 ) for identification of each point on the x- and y - axes in the present study , the quality factor ( qf ) was used to indicate the degree of loss in image quality , rather than the compression ratio ( cr ) . the first possibility is the selection of a qf in the compression scale of the software . however , it has to be emphasized that cr depends not only on the degree of image loss , but also on the image content of the original image . for example , a simple image would achieve higher cr than a more complex one at the same degree of image loss . therefore , cr might not be the most suitable parameter to be used for compression . expressing the information loss by the qf seems ideal as it is image content independent . the adobe photoshop software was used in this study for the jpeg2000 compression because it is well - known and easy to access . different versions of adobe photoshop ( adobe systems inc . , san jose , ca ) were also used by some of the previous authors . the qfs were not randomly selected ; rather , they were based on the study of abdelkarim et al . , and duarte et al . , who studied the effect of compression on landmark identification . we chose the landmarks based on previous researches including the points which did not show good reproducibility . the location of cephalometric points by the x - y coordinate system was used because this is an adequate methodology , previously tested and employed by different authors . cziraki et al . , reported loss of diagnostic accuracy on digital lateral cephalograms with a cr of 25:1 , whereas 12:1 was similar to the image without compression . duarte et al . , reported that jpeg images of lateral cephalograms with qfs 100 , 80 , and 60 , resulting in crs of 3.4:1 - 4.2:1,17:1 - 26:1 , and 30 - 62:1 , respectively , did not present alterations in the reproducibility of identification of cephalometric points compared with the dicom format . good reproducibility was achieved for the 12 points , except for point or on the x - axis . in a study by abdelkarim , the effect of jpeg2000 compression on landmark identification of lateral cephalometric digital radiographs was evaluated . the images included the original uncompressed tagged image file format ( tiff ) image and the jpeg2000 format at 3:1 , 12:1 , 50:1 , and 110:1 crs . all landmark identifications were precise with the exception of the maxillary incisal apex and edge at the 12:1 and 50:1 crs , respectively . they concluded that jpeg2000 is a reliable file format that can be implemented in orthodontic practice . wenger et al . , used an aluminum test object to assess the effect of the jpeg crs 60% , 70% , 80% , 90% , and 98% on direct digital cephalometric image quality . the results showed that jpeg compression does not have any effect on the perceptibility of landmarks . as previously mentioned in the present study , jpeg2000 images with the qfs 85 , 75 , and 60 , resulting in crs 11:3 - 15:7 , 17:1 - 26:7 , and 39:5 - 73:1 , respectively , did not present a statistically significant difference compared with dicom images [ table 3 ] , which seems to be in agreement with most of the results of the previous studies mentioned above . but it should be emphasized that comparing different studies is difficult because of the different softwares used for image compression and the difference in image acquisition techniques ( storage phosphor systems and charge coupled device based systems ) . even though jpeg has an international organization for standardization ( iso ) standard , its compression scale is not standardized . consequently , different programs , or even different versions of the same program , have different or even opposing compression scales . jpeg2000 images of lateral cephalograms with qfs 85 , 75 , and 60 did not demonstrate any alterations in the identification of cephalometric points compared with the dicom format .
background : with increase of digital imaging , the need for storage space and transmission speed also increases . 
 compressed images need less storage space and decrease the transmission time . however , compression could compromise image quality . 
 the aim of this study was to evaluate the influence of image compression on the identification of cephalometric points on direct digital lateral cephalogram images , compared with the digital imaging and communications in medicine ( dicom ) format.materials and methods : in this analytical - descriptive study , 19 direct digital lateral cephalograms saved in dicom format were used . 
 they were converted to joint photographic experts group ( jpeg ) 2000 format with quality factors 85 , 75 , and 60 adding up to 76 images ( dicom , jpeg 85 , 75 , and 60 ) . 
 the images were randomized and eight cephalometric points were identified on each image by a professional , using the x - y coordinate system . 
 analysis of variance ( anova ) was applied to investigate if there was a statistically significant difference in the location of cephalometric points between each group of images . 
 all tests were applied at a significance level of 5%.results : the results did not demonstrate any statistically significant difference in the identification of the eight cephalometric points between the dicom images and the jpeg2000 quality factors 85 , 75 , and 60.conclusion:jpeg2000 images of lateral cephalograms with quality factors 85 , 75 , and 60 did not demonstrate any alterations in the identification of cephalometric points compared with the dicom format . 
 jpeg2000 is a reliable file format for the compression of digital lateral cephalograms .