referring now to fig1 a raster memory 12 contains a full scale rasterized waveform image , i . e ., 1000 × 500 . the waveform image data is transferred from the raster memory 12 via a demultiplexer 14 to a compression circuit / algorithm 16 , which may be implemented as a field programmable gate array ( fpga ) as shown or as circuit elements or as a processing program in a digital signal processor ( dsp ). for vertical compression the demultiplexer 14 separates the waveform image data into separate lines of data in a recirculating manner , the number of separate line outputs being a function of the maximum desired compression — three line outputs for the present example having a maximum 3 : 1 compression . output from the compression circuitlalgorithm 16 is a video signal that is formatted according to an appropriate video standard required by a graphics chip 18 . the output from the graphics chip 18 drives a display 20 upon which the compressed waveform image and any applications and measurement packages are displayed for a viewer . since the compression of the waveform image occurs prior to the graphics chip 18 , the graphics chip only needs to perform up - scaling as required . although any compression factor may be implemented , and compression may be implemented either horizontally , vertically or both , fig3 shows a particular circuit configuration that provides up to 3 : 1 vertical compression , i . e ., the compression circuittalgorithm 16 for this example converts 500 vertical lines of the waveform image to a range of 167 - 500 vertical lines for the compressed display . the compression is done by looking at one , two or three lines at a time and converting all the corresponding pixels in those lines into single pixels for one compressed line . if there is a non - black pixel in any of the input lines for a given pixel location in the output line , that pixel shows up in the output line and its intensity is preserved . if two different intensity pixels in the input lines compete for the same location in the output line , the pixel with the higher “ priority ” is displayed in the output line . there is no averaging involved . in one particular implementation display data from the raster memory 12 is transferred in a 9 - bit format , as shown in fig4 , where five bits contain intensity content and the other four bits contain identification or priority content . for example the id content may merely be , for a four - input channel oscilloscope , the input channel from which the waveform image data was derived and a user then may prioritize the input channels for display via the oscilloscope user interface ( ui ). for oscilloscopes having a color display where the waveform data from each input channel is displayed in a distinct color , the id may also indicate what color is used to display that data as part of the waveform image . since data transfers generally are done in increments of 2 n , such as 16 - or 32 - bits , each 16 - bit data word from the raster memory includes the 9 - bit data word with the remaining bits being unused for informational purposes . the waveform image data from the raster memory 32 streams into an optional pre - fifo ( first - in , first - out ) buffer 22 that acts as a rate conversion buffer to get the input data into the clock domain of the logic doing the image compression . the pre - fifo buffer 22 is not necessary if only display compression is being done as then the compression logic may be run at the input clock rate . the data then streams sequentially via an input demultiplexer 24 into three line fifos 26 , 28 , 30 . at the output of the line fifos 26 , 28 , 30 is a redirection section 32 that aligns the outputs from the line fifos according to the desired compression factor — 1 : 1 , 2 : 1 or 3 : 1 in this example . there are three outputs from the redirection section 32 : a first output provides a 1 : 1 compression , a second output is input to a first pixel combiner 34 together with the 1 : 1 output to provide a 2 : 1 output , and a third output is input to a second pixel combiner 36 together with the 2 : 1 output to provide a 3 : 1 output . the three outputs are then input to an output multiplexer 38 which selects the particular compression output on a line - by - line basis for the output line according to the desired compression factor . for any compression factor where the output multiplexer 38 changes compression output selection from one output line to the next , i . e ., compression factors that are not integer ratios , the pattern of compression factors above and below a vertical midpoint is preferably symmetrical . a line input counter 40 provides a control signal to the input demultiplexer 24 that determines into which line fifo 26 , 28 , 30 the next line of waveform image data is input . in this example the line counter 40 steers the outputs of the input demultiplexer 24 after every 1000 data points in the present example to the next line fifo 26 , 28 , 30 in a constant loop , i . e ., transitions “ 1 , 2 , 3 , 1 , 2 , 3 , 1 , . . . ” etc . a remap counter 42 provides proper alignment of lines that are to be combined according to the desired compression factor for that particular output line , i . e ., if two lines are to be combined for a 2 : 1 compression then one line is delayed by one line period with respect to the other in the redirection section 32 . if the two lines to be combined happen to be from the line 3 fifo 30 and the line 1 fifo 26 , the redirection section 32 directs the delayed output from the line 3 fifo to the 1 : 1 output and the output from the line 1 fifo for input to the first pixel combiner 34 . finally a compression lookup table ( lut ) 44 provides a control signal to the output multiplexer 38 to select the compression output for the particular output line . as indicated above the compression lut 44 provides a control signal that allows selection of the compression output on an output line - by - line basis . the remap counter 42 increments by the number of lines that were previously processed so that the pixel combiners 34 , 36 are always lined up for the compression of the next input lines . after a whole line is processed , the compression lut 44 increments to the next entry or output line . this process allows the output image to be any size between 167 and 500 pixels vertically . the compressed output line is input to a video fifo 46 for conversion into the rgb565 color space and in this example the 9 - bit data words are converted into the 16 - bit format required for the rgb565 color space by an output lookup table ( lut ) 48 . the rgb565 video is sent to a thin film transistor ( tft ) format / control block 50 where it is then input to the video input port of the graphics chip 18 where up - scaling may be applied if necessary . fig5 a and 5 b illustrate the realtime display compression algorithm for simple examples , such as 2 . 0 × and 1 . 5 × compression factors . as is readily seen , the background black pixels are given a low priority so that any pixel of color including white is selected over the black pixel so that the intensity information is retained in the compressed output line . in the 2 . 0 × example every two pixels are combined according to the priority algorithm , so the compression lut 44 always selects the 2 : 1 compression output from the output multiplexer 38 , and the remap counter 42 keeps redirecting the line fifo outputs so that the output lines circulate as 1 / 2 , 3 / 1 , 2 / 3 , etc . with appropriate alignment line delays . for the 1 . 5 × example the compression lut 44 selects for alternate output lines the 2 : 1 and 1 : 1 outputs from the output multiplexer 38 , and the remap counter 42 keeps redirecting the line fifo output so that the output lines circulate as 1 / 2 , 3 , 1 / 2 , 3 , etc . fig6 shows a full scale waveform image view ( 1000 × 500 ). fig7 a , 7 b and 7 c show down - scaled waveform image views corresponding to compression factors of approximately 3 : 1 , 2 : 1 and 3 : 2 respectively . comparing these views , especially fig7 a , with the prior art image shown in fig1 , it is apparent that the dim and missing sections have been eliminated and the viewer is provided with a more pleasing display of the waveform image in the compressed form . although the above detailed description is for an example of vertical compression , the lines may also be compressed horizontally in a similar manner . the line fifos 26 , 28 , 30 are replaced with column fifos so the output from the input demultiplexer 24 provides successive data points of the waveform image data to the column fifos in the 1 , 2 , 3 , 1 , 2 , etc . loop pixel - by - pixel , the redirection section 32 operates on a pixel rather than a line basis to provide column outputs , and the compression lut 44 provides control to the output multiplexer 38 on a column - by - column basis . if both vertical and horizontal compression of the waveform image are desired , the vertical compression may be performed first followed by the horizontal compression . thus the present invention provides a realtime display compression circuit / algorithm that preserves pixel intensity for the waveform image when compressed by applying a priority algorithm to pixels that are combined vertically and / or horizontally rather than averaging , and then converting the pixels to video for input to a graphics chip for display .