- RPi Screens
- MIPI Display Serial Interface (MIPI DSI)
- The advantages of MIPI specifications in mobile, automotive and multimedia applications
- MIPI DSI to RGB Display Interface Bridge
- PPI vs. DPI: what’s the difference?
RPi ScreensBoth define the resolution, or clarity, of an image but each refers to separate media—that is, digital versus print. Understanding how they are different and how to apply each in your projects will empower you to produce a quality print, to optimize digital images for web and ultimately to save yourself valuable time. PPI describes the resolution in pixels of a digital image whereas DPI describes the amount of ink dots on a printed image. Though PPI largely refers to screen display, it also affects the print size of your design and thus the quality of the output. DPI, on the other hand, has nothing to do with anything digital and primarily concerns print. PPI, or pixels per inchrefers both to the fixed number of pixels that a screen can display and the density of pixels within a digital image. Pixel count on the other hand refers to the number of pixels across the length and width of a digital image—that is, the image dimensions in pixels. Zoom in to any image on your and you will see it break up into colored squares—these are pixels. Within pixels are sub-pixels, red, green and blue light elements that the human eye cannot see because additive color processing blends them into a single hue which appears on the pixel level. This does not exist in print—only in the electronic display of images, like television screens, computer monitors and digital photography. Use PPI whenever you are working with digital images. An image with a higher PPI tends to be higher quality because it has a greater pixel density, but exporting at PPI is generally considered industry standard quality. Printing an image on canvas does not require as high a resolution because details get lost in the texture of the material. PPI does not really matter for distribution on the web because the pixel density of your monitor is fixed. It is the pixel dimensions the amount of pixels from left to right, top to bottom that will determine the size and detail of your image. Raster programs software that work with pixel-based media like Photoshop have you set up the PPI resolution right at the beginning when you create a document. You will find Resolution listed with other parameters in the New Document window. If you need to increase the resolution on an image that has already been created, you can resample it. Resampling is the process of changing the amount of pixels in an image, in which the software will create or delete pixels to preserve image quality. In the Image Size window, you will have options for changing the width, height and PPI resolution of your image. You can decrease the resolution if you set the PPI to a lower value. As the pixel count decreases, the image size and dimensions decrease as well. You increase the resolution when you set PPI to a higher value. This allows the image to be printed at a larger print size. That said, it is best to avoid changing the PPI on an existing image whenever possible. The resampling process requires Photoshop to generate new pixels from scratch. Thus, computer generated pixels can create unintentional results on your image. DPI, or dots per inch, refers to the resolution value of a physical printer.
MIPI Display Serial Interface (MIPI DSI)
The advantages of MIPI specifications in mobile, automotive and multimedia applications
A look at the ways in which the evolving MIPI standard is being used to provide connectivity in automotive, mobile, multimedia, virtual reality, augmented reality and related applications. One of the most important of these is MIPI, a set of standards that make it easier to implement common features of smartphones such as displays and imaging devices. The ubiquity and power of MIPI has not gone unnoticed in adjacent markets, especially those that are adding features such as image sensors and displays. These include the automotive market, which is using a lot more image sensors as advanced driver assistance systems, such as lane-keeping warnings, are implemented as cars evolve toward full autonomy. The same architecture carries over into the automotive world, in features such as intelligent rear-view mirrors, wing mirrors and even surround-view systems. An Ethernet link would then make the longer-distance connections from the modules to a central processor, which would provide the ADAS functionality and drive a display over the DSI interface. A similar architecture can also be adapted for use in virtual-reality VRaugmented-reality AR and mixed-reality MR displays, for use by the medical, industrial, maintenance, and home maintenance professions, and in consumer applications. More powerful versions of these processors would also receive inputs from, and drive, displays over DSI links. Data is transmitted using differential signals, with a dedicated clock, and the physical layer of the interface is a D-PHY, also defined in the MIPI specs. Given that the image is held in a frame buffer see Figure 2a packet builder will take one of the lines from that buffer and start building a packet. This enables multiple streams of data to flow over the same link, using the virtual channel identification to distinguish which stream each packet belongs to. After the payload of image data, there is a CRC field. At the receiving end, the packet is received and sent to the packet decoder where it is checked, errors are recovered and the resultant image data sent to the receiving frame buffer. The process continues until all the data lines have been transferred. Between each packet, the link goes into a low-power state in which it remains until more data needs to be sent. DSI is a high-speed serial interface between a peripheral and a host processor, receiving parallel data from the host and serializing it. On the receiving end, the reverse process happens to recover the parallel data. The DSI host will encapsulate the pixel data and control information into a packet format and send it to a display. There are two main operating modes in DSI — command mode and video mode. In command mode, it is assumed that the display has a local frame buffer to which the host can write. The host uses command mode to write to or read from the register and frame buffer memory by using DCS commands or other vendor-defined commands. In video mode, the host transfers a real-time pixel stream to the peripheral, which expects a constant flow of video data and synchronization information. MIPI DSI defines packets not only to transport pixel data, but also to transport the event information vertical sync, horizontal sync. When the host side is driven with a DPI interface, the packet builder will detect the rising edge of a vertical sync signal and create a packet that includes detailed information indicating that it is a protocol sync event. As in CSI-2, the packet will be sent to a lane distribution controller, where it will be converted into D-PHY packets and sent across the link. At the other end it will be recovered, and the event will be sent to the logic that is driving the display. A similar thing happens with the horizontal sync signal. This creates a data structure that represents an image frame with the associated horizontal and vertical sync signals, image data and blanking periods. These blanking periods can then be used in a number of ways, for example to send the link into a low-power state, to carry non-video packets, such as display configuration data or video packets for a different virtual channel. This approach requires multiple sideband signals, for example for interrupts, chip selects and enables. It builds on the two-wire simplicity of I2C and the high-speed, low-power nature of SPI and adds features such as in-band interrupt, built-in command support, dynamic addressing, advanced power management, and high data rates, while maintaining backwards compatibility with I2C sensors.
MIPI DSI to RGB Display Interface Bridge
Back to the Hub. Hardware - detailed information about the Raspberry Pi boards. Hardware History - guide to the Raspberry Pi models. Cases - lots of nice cases to protect the Raspberry Pi. Other Peripherals - all sorts of peripherals used with the Raspberry Pi. A number of people have used a Motorola Atrix Lapdock to add a screen and keyboard with trackpad to RasPi, in essence building a RasPi-based laptop computer. Lapdock is a very clever idea: you plug your Atrix smart phone into Lapdock and it gives you an The smart phone acts as a motherboard with "good enough" performance. Motorola also made a Lapdock for the Motorola Droid Bionic smartphone. There's also a good 'blog entry at element14 with photos and suggestions of where to get cables and adapters: Raspberry Pi Laptop. The hardest part about connecting Lapdock is getting the cables and adapters. These are unusual cables and adapters, so check the links. If it's not, Lapdock is powered off. As soon as you plug in a phone or RasPi, all the grounds short together and Lapdock powers itself on. Many cheap HDMI cables do not include the individual ground lines, and rely on a foil shield connected to the outer shells on both ends. Such a cable will not work with an unmodified Lapdock. The 'blog describes a side-benefit of this feature: you can add a small power switch to Lapdock so you can leave RasPi attached all the time without draining the battery. Lapdock is not USB compliant since it provides upstream power on its Vbus pin. Lapdock uses this to charge the Atrix phone. You can use this feature to power RasPi if you have a newer RasPi. Newer RasPis replace F1 and F2 with zero Ohm jumpers or eliminate them entirely, which allows Lapdock to provide power. If you don't mind modifying your original RasPi, you can add shorting jumpers over F1 and F2 or replace them with higher-current fuses. What gets powered on depends on whether Lapdock is open or closed. If it's open, the screen and all Lapdock USB ports are powered. This is for charging an Atrix phone. When you open or close Lapdock, the Micro USB power switches off for about a second so if your RasPi is connected it will reboot and you may have a corrupted file system. There's discussion about this at the RasPi forum link, and someone has used a supercapacitor to work around the problem: Raspberry Pi lapdock tricks. In the latter case the device may initially appear to work, but there will be a problem, as the HDMI specs only provide in a maximum of 50mA 5 Volt from the HDMI port, but all of these adapters try to draw much more, up-to mA, in case of the R-PI there is a limit of mA that can be drawn safely, as mA is the limit for the BAT54 diode D1 on the board. The solution is to either only use externally powered converters, or to replace D1 with a sturdier version, such as the PMEGAET, and to replace the power input fuse F3 with a higher rated one, as the current one is only mA, and the adapter may use mA itself. Also notice that the R-PI's power supply also must be able to deliver the extra current. Beagleboard people have reported various levels of success mainly "issues" :. Alternatively, it may be possible to design an expansion board that plugs into the LCD headers on the R. Here is something similar for Beagleboard:. The SOC system on a chip does not support any kind of analog component video, including VGA, since the SOC is designed for mobile phone use where this would not be a requirement.