Application Note
AN_339
Using JPEGs with the FT800 series
Version 1.0
Issue Date: 2014-10-15
This document discusses JPEG files and how to check that they are
compatible with the FT800 series. The methods that can be used to display a
suitable JPEG image using the FT800 series are also discussed.
Use of FTDI devices in life support and/or safety applications is entirely at the user’s risk, and the
user agrees to defend, indemnify and hold FTDI harmless from any and all damages, claims, suits
or expense resulting from such use.
Future Technology Devices International Limited (FTDI)
Unit 1, 2 Seaward Place, Glasgow G41 1HH, United Kingdom
Tel.: +44 (0) 141 429 2777 Fax: + 44 (0) 141 429 2758
Web Site: http://ftdichip.com
Copyright © 2014 Future Technology Devices International Limited
Application Note
AN_339 Using JPEGs with the FT800 series
Version 1.0
Document Reference No.: FT_001106
Clearance No.: FTDI#415
Table of Contents
1
2
3
4
Introduction .................................................................................................................................... 2
1.1
Scope ....................................................................................................................................... 2
1.2
Software Required .................................................................................................................. 2
1.3
Hardware Required ................................................................................................................. 2
JPEG Basics ...................................................................................................................................... 3
2.1
Background ............................................................................................................................. 3
2.2
Markers ................................................................................................................................... 3
2.3
Baseline v Progressive ............................................................................................................. 5
Using JPEGs with the FT800 series .................................................................................................. 6
3.1
Methods to display a suitable JPEG image ............................................................................. 6
3.2
CMD_LOADIMAGE .................................................................................................................. 7
3.3
JPEG constraints for the FT800 series ..................................................................................... 7
Using JPEGs with the FT800 series .................................................................................................. 8
4.1
Using the Sample Code ........................................................................................................... 8
4.2
Main Functions of Sample Code ............................................................................................. 9
5
Conclusion ..................................................................................................................................... 12
6
Contact Information...................................................................................................................... 13
Appendix A – References ...................................................................................................................... 14
Document References....................................................................................................................... 14
Acronyms and Abbreviations ............................................................................................................ 14
Appendix B – List of Tables & Figures ................................................................................................... 15
List of Tables ..................................................................................................................................... 15
List of Figures .................................................................................................................................... 15
Appendix C – Revision History .............................................................................................................. 16
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1 Introduction
JPEG commonly refers to the popular image file format which reduces file size by compressing the
raw data according to the specifications defined by the Joint Photographic Experts Group (JPEG).
File extensions are usually .jpg or .jpeg. The FT800 series can process baseline JPEGs directly and
display the images, provided that the amount of processed data is not larger than the capacity of
the FT800 series’s graphics RAM (256kB). Note that the JPEG specification refers to a range of
compression options, not the file structure used to store the data, but the term JPEG is generally
applied to both. One such file structure is the JPEG File Interchange Format (JFIF), first published
in 1992. Another is Exif which extends the metadata available recorded for an image, for example
to include camera type, shutter speed, etc.
1.1 Scope
This document covers the basics of JPEG file use with the FT800 series. It shows how to check the
compatibility of a JPEG file and provides an example application, built using Visual Studio Express
2013, to quickly load and display valid JPEG files using the FT800 series. Further details on the
FT800 series are available in the FT800 & FT801 datasheets and the FT800 Series Programmer
Guide.
1.2 Software Required
Microsoft Visual Studio Express 2013 for Windows Desktop which can be downloaded from:
http://www.microsoft.com/en-gb/download/details.aspx?id=40787
FTDI D2XX driver which can be downloaded from:
http://www.ftdichip.com/Drivers/D2XX.htm
Sample application ‘Single JPEG Viewer’ which can be downloaded from:
http://www.ftdichip.com/Support/SoftwareExamples/EVE/FT800_Single_JPEG_Viewer.zip
1.3 Hardware Required
PC with Windows OS installed. Visual Studio Express 2013 supports Windows 7 Service Pack 1,
Windows 8, Windows 8.1, Windows Server 2008 R2 SP1, Windows Server 2012 & Windows Server
2012 R2. Further PC hardware requirements are stated on the Visual Studio Express 2013
download page.
FT800 or FT801 development module with LCD panel: VM800B or VM800C, with either 4.3” or 5.0”
display (WQVGA 480 x 272), or 3.5” display (QVGA).
FTDI MPSSE cable: C232HM-DDHSL-0.
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2 JPEG Basics
2.1 Background
The origins of JPEG date back to the early 1980s when the International Standards Organization
(ISO) set up the Photographic Experts Group (PEG) to investigate ways to transmit image and
graphics data over digital networks. This group later combined with a CCITT subgroup researching
a similar area to form the Joint Photographic Experts Group (JPEG). The JPEG standard first
appeared in 1991, but this did not specify a file format for the interchange of JPEG data. The JPEG
File Interchange Format (JFIF), Version 1.02, was published in September 1992 by Eric Hamilton,
then of C-Cube Microsystems. The aim was to provide a means to readily exchange JPEG
bitstreams between a range of platforms. The exchangeable image file format (Exif) was first
released in 1998. For JPEGs, this adds further metadata, e.g. camera information, exposure time,
etc., in comparison to JFIF. The JPEG specification does define a lossless compression technique,
but typically JPEGs are lossy to take full advantage of their ability to greatly reduce file size whilst
still maintaining an acceptable image quality. JPEG compression is particularly suited to
photographic images. Note that the JPEG standard does not specify a single technique, but rather
a range of compression options, however most JPEGs encountered will be ‘baseline’ format which
uses Huffman encoding and 8-bit sample data.
2.2 Markers
A JPEG file is comprised of a series of segments. The beginning of a segment is designated by a
‘marker’ which consists of an 0xFF byte followed by a further byte (which is not equal to 0x00 or
0xFF) which defines the marker type. The first two bytes in a JPEG file are the ‘Start of Image’
(SOI) marker, 0xFFD8, and the last two bytes are the ‘End of Image’ (EOI) marker, 0xFFD9. The
presence of the S0F0 marker indicates a baseline image. This marker also contains the image
height and width. Table 1 below lists some common JPEG markers.
Marker
Abbreviation
Description
0xFFD8
SOI
Start of Image
0xFFFE
COM
Comment
0xFFDB
DQT
Define Quantisation Table
0xFFC0
S0F0
Start of Baseline DCT Frame
0xFFC2
SOF2
Start of Progressive DCT Frame
0xFFC4
DHT
Define Huffman Table
0XFFDA
SOS
Start of Scan
0xDDF9
EOI
End of Image
Table 1 Common JPEG markers
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Some markers are ‘stand-alone’ (e.g. SOI) and another marker follows directly. Other markers
(e.g. S0F0) contain a payload, the size of which is given by the first two bytes following the
marker (the size reported includes the two ‘size bytes’, but not the two marker bytes) . Note that a
JPEG file can contain more than one S0F0 (baseline) marker, for example, the file may also
contain a thumbnail image which will also have an S0F0 marker. Each marker will contain height
and width data for their respective images. Also, a JPEG file may contain both an S0F0 marker and
an S0F2 marker, for example, a thumbnail may be stored as a baseline JPEG whilst the main
image is progressive.
JPEG files can also contain up to sixteen ‘application markers’ (APP0 to APP15) which are
designated by a 0xFF byte followed by a further byte which takes a value between 0xE0 and 0xEF.
The next two bytes indicate the length of the segment corresponding to this marker (similar to the
previous markers the length includes the two ‘length bytes’ themselves, but not the two marker
bytes). Decoders can read or skip over these application markers as required.
JFIF format JPEG files include an application marker (APP0), equal to 0xFFE0, which is used to
identify it as a JPEG JFIF file. The segment defined by this marker also includes the five byte JFIF
identifier (0x4A 46 49 46 00). Exif JPEG files include the ‘APP1 marker’, equal to 0xFFE1. This
segment includes an identifier (the six bytes 0x45 78 69 66 00 00) which can be used to
determine if the format is Exif. Figure 2.1 shows an extract from the start of a JPEG (JFIF) file.
Figure 2.1 Extract from a JPEG (JFIF) file showing markers.
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2.3 Baseline v Progressive
Baseline JPEGs are displayed line by line beginning from the top left of the image and finishing at
the bottom right. The result is that only a partial image may be seen if downloading a baseline
JPEG over a slow internet connection – see figure 2.2.
Figure 2.2 Baseline JPEG.
Progressive JPEGs are displayed in a series of scans with the picture detail increasing each time.
The whole image, albeit blurred, appears first and then becomes clearer – see figure 2.3. In
comparison to a baseline JPEG, it is possible to see the whole image earlier when downloading a
progressive JPEG over a slow internet connection.
Figure 2.3 Progressive JPEG.
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3 Using JPEGs with the FT800 series
3.1 Methods to display a suitable JPEG image
There are two methods to display a suitable JPEG image using the FT800 series. The first method
is to use the image conversion utility (img_cvt) to transform the JPEG file into a format which can
either be loaded directly (or via the coprocessor CMD_INFLATE in the case of the zlib compressed
option) to the FT800 series graphics RAM. This utility allows the conversion format to be specified
(e.g. RGB565), therefore this can be optimised to take into account the storage available in
graphics RAM and the image quality required. Application note AN 303 has more details on using
the img_cvt utility. The second method is to read the JPEG file into the FT800 using the coprocessor function CMD_LOADIMAGE. This function will decode the JPEG file, produce either
RGB565 or L8 bitmap data and store this in graphics RAM. Figure 3.1 outlines the two JPEG
processing options for the FT800 series.
Figure 3.1 FT800 series JPEG processing options
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3.2 CMD_LOADIMAGE
The destination starting address in graphics RAM for the converted bitmap and whether the image
should be in RGB565 or L8 format is specified in CMD_LOADIMAGE. The JPEG file data stream
should then follow directly into the command buffer. An example sequence using the FTDI
Hardware Abstraction Language (HAL) is shown below:
Ft_Gpu_Hal_WrCmd32(phost, CMD_LOADIMAGE);//Load a JPEG image via command processor
Ft_Gpu_Hal_WrCmd32(phost, 0L);//Destination starting address in Graphics RAM
Ft_Gpu_Hal_WrCmd32(phost, 0);//Options 0 for RGB565, 1 for L8 monochrome,
//2 for RGB565 with no display list commands, 3 for L8 with no display list commands
Ft_Gpu_Hal_WrCmdBuf(phost, jpeg_data, number of bytes);//write data in command buffer
CMD_LOADIMAGE also writes commands to the display list to set the source, layout and size of the
image (BITMAP_SOURCE, BITMAP_LAYOUT and BITMAP_SIZE). [Note that only a BEGIN and
VERTEX2F (or VERTEX2II) display list commands are then required to complete the display list
needed to render the image.] The parameter OPT_NODL can be set to suppress the creation of the
display list commands by CMD_LOADIMAGE. To invoke this mode, set the options parameter to 2
for RGB565 and 3 for L8 format.
If the number of bytes in the JPEG file to be written to the command buffer is not a multiple of
four, then one, two or three bytes (of any value) should be added to ensure four-byte alignment of
the next command.
For more details on CMD_LOADIMAGE, please see the FT800 Series Programmer Guide.
3.3 JPEG constraints for the FT800 series
The FT800 series can only process baseline JPEG images. Progressive JPEG or JPEG 2000 images
are not supported and if supplied to CMD_LOADIMAGE will cause the FT800 series co-processor
engine to stop accepting new commands. For details on how to recover, please see section 5.5 of
the FT800 series Programmer Guide. The processed data must not be larger than the FT800’s
graphic RAM size of 256kB.
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4 Using JPEGs with the FT800 series
This sample code is based on the FTDI HAL and will display a suitable JPEG file saved in the folder
‘test’. The image will be centred on the display.
Prior to reading the JPEG file into the FT800 using CMD_LOADIMAGE, the image height and width
are extracted and checked that they are compatible with the display’s dimensions. If the image is
a progressive JPEG then it is not passed to the FT800 and an error message is reported.
The default display selection is for a WQVGA (480 x 272) panel, as supplied with the 4.3” and 5.0”
basic and credit card modules. The 3.0” QVGA panel can be selected by choosing the appropriate
#define in FT_Platform.h.
4.1 Using the Sample Code
Download the sample code from FT800_Single_JPEG_Viewer_1.0.zip and unzip. Copy the JPEG file
for display to the folder ‘Test’. If the folder contains more than one JPEG, then only the first JPEG
(ordered by file name) will be used. Download the latest FTDI driver for Windows. Connect the
MPSSE cable’s fly leads to the FT800 series module using the connections in Table 1 below. (Note
that the cable also supplies power to the module via the 3.3V pin — disconnect this pin if not
required.). Now connect the MPSSE cable to the PC. Open the Visual Studio Solution
(FT_single_jpg_viewer.sln) located in the directory Project/Msvc_win32/FT_single_jpg_viewer,
build and then run the application. The selected JPEG should appear on the module’s display. An
error message will be reported on the FT800 series display if there are no files in ‘Test’, the file is
not a JPEG, the file is not a baseline JPEG, or the image is the wrong dimensions for the screen.
MPSSE cable Signal Name
Colour
SCK
ORANGE
MOSI
YELLOW
MISO
GREEN
CS#
BROWN
INT#
PURPLE
PD#
BLUE
3.3V
RED
GND
BLACK
Table 2 MPSSE cable to FT800 series connections
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4.2 Main Functions of Sample Code
//*******************************
ft_uint16_t Ft_List_Out_files()
//*******************************
// Find *.jp* file & ensure file size is a multiple of 4 bytes
{
//ft_uint16_t nooffiles=0;
char *path = "..\\..\\..\\Test"; //Look for *.jp* files in Test directory
struct _finddata_t Files;
long file_spec;
if (!_chdir(path))
{
if ((file_spec = _findfirst("*.jp*", &Files)) == -1L)
{
return nooffiles;
}
else
{
ft_strcpy_P(Image_prop[nooffiles].name, Files.name);
//ensure file size is a multiple of 4 bytes
Image_prop[nooffiles].file_size = (Files.size + 3)&~3;
nooffiles++;
}
}
return nooffiles;
}
//*********************
ft_void_t Load_JPEG()
//*********************
{
ft_uint8_t imbuff[8192];
ft_uint16_t blocklen;
ft_uint8_t error_code = 0;
ft_uint16_t xcoord;
ft_uint16_t ycoord;
ft_uint8_t markerID[2];
ft_uint8_t marker_info[8];
ft_uint8_t marker_next_byte[8];
ft_uint16_t size[8] = { 0 };
//read first 2 bytes to check for JPEG SOI marker 0xFFD8
fseek(pfile, 0, SEEK_SET); // Beginning of file
fread(&markerID, 1, 2, pfile); //read first 2 bytes
if (((markerID[0] << 8) + markerID[1]) != 0xFFD8)
{
error_code = 1; //No SOI marker (0xFFD8) detected
}
else
{
while (fread(&markerID, 1, 1, pfile) > 0)
{
if (markerID[0] == 0xFF)
{
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fread(&marker_next_byte, 1, 1, pfile);
if (marker_next_byte[0] >> 4 == 0xE){ //APPn marker found if true
fread(&marker_info, 1, 2, pfile); //read APPn marker length
fseek(pfile, ((marker_info[0]*256) + marker_info[1]-2), SEEK_CUR); //skip APPn marker
}
if (marker_next_byte[0] == 0xC0){ //baseline JPEG marker found
fread(&marker_info, 1, 8, pfile); //read next 8 bytes & extract height & width
image_height = marker_info[3]*256 + marker_info[4];
image_width = marker_info[5]*256 + marker_info[6];
printf("image_height = %d\n", image_height);
if (image_height > FT_DispHeight) error_code = 2; //Max is 272 for WQVGA, 240 for QVGA
printf("image_width = %d\n", image_width);
if (image_width > FT_DispWidth) error_code = 2; //Max is 480 for WQVGA, 320 for QV
}
if (marker_next_byte[0] == 0xC2){ //check if progressive JPEG
error_code = 3;
}
}
}
}
if (error_code != 0) { //error flagged, display message
fclose(pfile);
/* close the opened JPEG file */
Ft_CmdBuffer_Index = 0;
Ft_Gpu_CoCmd_Dlstart(phost);
Ft_App_WrCoCmd_Buffer(phost, CLEAR(1, 1, 1));
Ft_App_WrCoCmd_Buffer(phost, COLOR_RGB(255, 255, 255));
if (error_code == 1) Ft_Gpu_CoCmd_Text(phost, FT_DispWidth / 2, FT_DispHeight / 2, 26,
OPT_CENTERX | OPT_CENTERY, "Error: Selected file is not a JPEG!");
if (error_code == 2) Ft_Gpu_CoCmd_Text(phost, FT_DispWidth / 2, FT_DispHeight / 2, 26,
OPT_CENTERX | OPT_CENTERY, "Error: Image size is not compatible!");
if (error_code == 3) Ft_Gpu_CoCmd_Text(phost, FT_DispWidth / 2, FT_DispHeight / 2, 26,
OPT_CENTERX | OPT_CENTERY, "Error: Selected file is a progressive JPEG!");
Ft_App_WrCoCmd_Buffer(phost, DISPLAY());
Ft_Gpu_CoCmd_Swap(phost);
Ft_App_Flush_Co_Buffer(phost);
Ft_Gpu_Hal_WaitCmdfifo_empty(phost);
}
else
{
//no error, therefore load image into FT800 via command processor
Ft_Gpu_Hal_WrCmd32(phost, CMD_LOADIMAGE); //Load a JPEG image via command processor
Ft_Gpu_Hal_WrCmd32(phost, 0L); //Destination starting address in Graphics RAM
Ft_Gpu_Hal_WrCmd32(phost, 0); //Options 0 for RGB565, 1 for L8 monochrome,
//2 for RGB565 with no display list commands, 3 for L8 with no display list commands
fseek(pfile, 0, SEEK_SET);
while (filesize > 0)
{
blocklen = filesize > 8192 ? 8192 : filesize;
/*copy the data into imbuff and then transfter it to command buffer*/
fread(imbuff, 1, blocklen, pfile);
filesize -= blocklen; //reduce filesize by blocklen
Ft_Gpu_Hal_WrCmdBuf(phost, imbuff, blocklen); //write JPEG file to command buffer
}
fclose(pfile);
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/* close the opened JPEG file */
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//centre image on display
xcoord = (FT_DispWidth/2) - (0.5*image_width);
ycoord = (FT_DispHeight/2) - (0.5*image_height);
Ft_CmdBuffer_Index = 0;
Ft_App_WrCoCmd_Buffer2(phost, CLEAR(1, 1, 1)); //clear screen to predefined values
/*Display list commands in this section are generated by CMD_LOADIMAGE unless option
//is set to 2 or 3
Ft_App_WrCoCmd_Buffer(phost, BITMAP_SOURCE(0L)); //specify the source address of
//bitmap in RAM_G
//specify bit map format, linestride and height for RGB565
Ft_App_WrCoCmd_Buffer(phost, BITMAP_LAYOUT(RGB565, image_width * 2, image_height));
//specify bit map format, linestride and height for L8
Ft_App_WrCoCmd_Buffer(phost, BITMAP_LAYOUT(L8, image_width * 1, image_height));
// controls drawing of bitmap
Ft_App_WrCoCmd_Buffer(phost, BITMAP_SIZE(NEAREST, BORDER, BORDER, image_width,
image_height));*/
Ft_App_WrCoCmd_Buffer(phost, BEGIN(BITMAPS));
Ft_App_WrCoCmd_Buffer(phost, VERTEX2II(xcoord, ycoord, 0, 0));
Ft_App_WrCoCmd_Buffer(phost, DISPLAY());//ends the display,commands after this ignored
Ft_Gpu_CoCmd_Swap(phost);
Ft_App_Flush_Co_Buffer(phost);
}
}
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5 Conclusion
The FT800 series can work with compatible JPEG files directly, or via the image converter utility
available from the FTDI website. In each case the JPEG data is converted into a bitmap which is
stored in the graphics RAM of the FT800 series. This bitmap can then be displayed using either
display list or co-processor commands.
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6 Contact Information
Head Office – Glasgow, UK
Branch Office – Tigard, Oregon, USA
Future Technology Devices International Limited
Unit 1, 2 Seaward Place, Centurion Business Park
Glasgow G41 1HH
United Kingdom
Tel: +44 (0) 141 429 2777
Fax: +44 (0) 141 429 2758
Future Technology Devices International Limited
(USA)
7130 SW Fir Loop
Tigard, OR 97223-8160
USA
Tel: +1 (503) 547 0988
Fax: +1 (503) 547 0987
E-mail (Sales)
E-mail (Support)
E-mail (General Enquiries)
[email protected]
[email protected]
[email protected]
E-Mail (Sales)
E-Mail (Support)
E-Mail (General Enquiries)
[email protected]
[email protected]
[email protected]
Branch Office – Taipei, Taiwan
Branch Office – Shanghai, China
Future Technology Devices International Limited
(Taiwan)
2F, No. 516, Sec. 1, NeiHu Road
Taipei 114
Taiwan , R.O.C.
Tel: +886 (0) 2 8791 3570
Fax: +886 (0) 2 8791 3576
Future Technology Devices International Limited
(China)
Room 1103, No. 666 West Huaihai Road,
Shanghai, 200052
China
Tel: +86 21 62351596
Fax: +86 21 62351595
E-mail (Sales)
E-mail (Support)
E-mail (General Enquiries)
E-mail (Sales)
E-mail (Support)
E-mail (General Enquiries)
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
Web Site
http://ftdichip.com
System and equipment manufacturers and designers are responsible to ensure that their systems, and any Future Technology
Devices International Ltd (FTDI) devices incorporated in their systems, meet all applicable safety, regulatory and system-level
performance requirements. All application-related information in this document (including application descriptions, suggested
FTDI devices and other materials) is provided for reference only. While FTDI has taken care to assure it is accurate, this
information is subject to customer confirmation, and FTDI disclaims all liability for system designs and for any applications
assistance provided by FTDI. Use of FTDI devices in life support and/or safety applications is entirely at the user’s risk, and the
user agrees to defend, indemnify and hold harmless FTDI from any and all damages, claims, suits or expense resulting from
such use. This document is subject to change without notice. No freedom to use patents or other intellectual property rights is
implied by the publication of this document. Neither the whole nor any part of the information contained in, or the product
described in this document, may be adapted or reproduced in any material or electronic form without the prior written consent
of the copyright holder. Future Technology Devices International Ltd, Unit 1, 2 Seaward Place, Centurion Business Park,
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Appendix A – References
Document References
FT800_Single_JPEG_Viewer.zip
FT800 Series Programmer Guide
FT800 Datasheet
FT801 Datasheet
img_cvt
C232HM-DDHSL-0 MPSSE Cable Datasheet
Latest FTDI drivers
AN 303
Acronyms and Abbreviations
Terms
Description
CCITT
The International Telegraph and Telephone Consultative Committee
Exif
Exchangeable image file format
ISO
International Standards Organization (now the International Organization
for Standards)
JFIF
JPEG file interchange format
JPEG
Joint Photographic Experts Group
L8
8-bit grayscale image
MPSSE
Multi-Protocol Synchronous Serial Engine
QVGA
Quarter Video Graphics Array
RAM_G
RGB
FT800 series graphics RAM
Red Green Blue
RGB565
Bitmap with 5 bits for red, 6 bits for green and 5 bits for blue, for each
pixel, to give a total of 65536 colours.
WQVGA
Wide Quarter Video Graphics Array
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Appendix B – List of Tables & Figures
List of Tables
Table 1 Common JPEG markers ............................................................................................ 3
Table 2 MPSSE cable to FT800 series connections ................................................................... 8
List of Figures
Figure 2.1 Extract from a JPEG (JFIF) file showing markers. ..................................................... 4
Figure 2.2 Baseline JPEG. ..................................................................................................... 5
Figure 2.3 Progressive JPEG. ................................................................................................ 5
Figure 3.1 FT800 series JPEG processing options..................................................................... 6
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Clearance No.: FTDI#415
Appendix C – Revision History
Document Title:
AN_339 Using JPEGs with the FT800 series
Document Reference No.:
FT_001106
Clearance No.:
FTDI#415
Product Page:
http://www.ftdichip.com/FTProducts.htm
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Date
2014-10-15
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