In Camera Processing From Sensor to Memory Card

Transcription

1 In Camera Processing From Sensor to Memory Card

2 Review of How Sensors Work The Photodiode converts the energy of incoming light (photons) into an electrical charge The Electron to Voltage Converter converts the electrical charge into voltage The Amplifier strengthens the voltage signal and transfers the signal to the ADC The Analog to Digital Converter classifies the analog voltage into digital data. The Output Register transfers the information into the camera s buffer.

3 Buffer The camera s buffer consists of RAM memory which temporarily holds the image information. The buffer will determine: The time between shots How many shots that can be taken in sequence when shot using continuous shooting mode. They are three types of buffers 1. Before image processing 2. After image processing 3. Smart image processing

4 Before Image Processing Buffer RAW data is placed directly into the buffer Images are then processed and then written to the storage card The number of frames per second (fps) which can be shot cannot be increased by changing the file format (RAW, TIFF, JPEG) The number of frames per second (fps) is independent of the image processing speed until the buffer is full

5 After Image Processing Buffer RAW data is first processed and converted into their final output format before they are placed in the buffer Therefore, the number of frames per second (fps) which can be shot in a burst will vary depending on the file format chosen. (RAW, TIFF, JPEG)

6 Smart Image Processing Buffer Combines elements from both After & Before buffering The RAW image is placed directly into the buffer Allows higher frames per second (fps) The images are then processed (TIFF or JPEG) and transferred back to the buffer Therefore, the image processing is not bottlenecked by the writing to the storage card or by processing

7 In Camera Processing Overview

8 In Camera Processing: RAW Images The captured data goes through: Color Interpolation Transferred to the camera s buffer. The image file is written directly to the memory card. *The RAW image file includes Meta data information including camera settings, date, time, ect.

9 Digital Image Formation In Camera Processing: TIFF Images The captured data goes through: Color Interpolation Color Temperature & White Balance Adjustment Noise Reduction, Tonal Curve Sharpening

10 In Camera Processing: JPEG Images The captured data goes through: Color Interpolation Color temperature & White Balance adjustment Noise Reduction Tonal Curve Sharpening Compression, which reduces file size and image quality

11 In Camera Processing Special Note: Camera s Display No matter what file format type: RAW, TIFF, JPEG all image data is sent through Color Interpolation, Color Temperature & White Balance settings for the image preview on the camera s LCD but this information is temporary and not written to the image file.

12 In Camera Processing: Color Interpolation Color Interpolation estimates the missing information for each color channel and creates the missing information.

13 In Camera Processing: White Balance White Balance compensates for the Kelvin Temperature of different light sources that effect the color quality of the image. The camera uses the color white as a reference point and calculates all the other colors based on pure white.

14 In Camera Processing: Noise Reduction

15 In Camera Processing: Types of Sensor Noise Dark Current Noise Readout Noise Fixed Pattern Noise

16 Dark Current Noise Is created by the activity of the sensor itself when the camera is turned on. This generates additional electrons that cause noise Increases with the temperature of the sensor Decreases as more light exposes the pixel (intensity)

17 Readout Noise Amplification is the main cause Is the statistical variations that happen between the time that the light photons are captured by the photodiode and the ADC conversion. Increases with speed

18 Fixed Pattern Noise CMOS sensors have one amplifier per pixel therefore the pixels cause Fixed Pattern Noise But because it has a fixed pattern it can be reduced more easily during noise reducing processes during in-camera image processing. CCD sensors have one amplifier per sensor so fixed pattern noise is not a major problem.

19 Noise Summary Increases as you increase the ISO (sensitivity) of the camera Red and Blue channels will have more noise because these channels are amplified more than the green channel. Why? Noise is most visible in uniform surfaces such as blue sky and shadows. Increases as pixel size decreases. Professional grade cameras use more advance noise removal algorithms to reduce noise.

20 Camera s Tonal Curve Digital cameras apply a Tonal Curve to the linear RAW data so that the data is similar to the perception of human vision and when printed or viewed on a monitor the image will appear more pleasing.

21 Camera s Tonal Curve Two types of correction that results from tonal curve adjustment Applies Gamma Correction to adjust contrast. (Gamma = Contrast) Applies Dynamic Range Compression to compensate for the characteristics of human vision. (Dynamic Range = Total image tonality from shadows to highlights)

22 Camera s Tonal Curve Sensor: Linear Human Vision: Non Linear

23 Tonal Curve Summary Digital data is recorded linear. Human perception of light is nonlinear. Human vision amplifies the shadows and compresses the highlights Gamma corrects tonality by changing the overall contrast. Dynamic Range Compression alters the data to better match human vision. Tonal Curves can be applied to RAW images using conversion software during image processing. This allows you the control of the full dynamic range of the sensor.

24 File Size Interpolation Interpolation = Up-sampling = Re-sampling Some digital cameras use interpolation to produce a larger file size than the camera s sensor can capture. File size interpolation increases the number of pixels in an image Example: the camera interpolates 6 million pixels of information based on the capture of 3 million pixels on the sensor. In-camera interpolation is of better quality than those performed on your computer because it is done before JPEG compression. Also used in digital zoom. The most common use of in-camera interpolation today, mostly in compact digital cameras.

25 File Size Interpolation Interpolation = Up-Sampling = Re-Sampling Determines the value of a new pixel based on a weighted average of the 4 pixels in the nearest 2X2 neighborhood of the pixel in the original capture.

26 Sharpening Optical Sharpness is defined by the quality of the lens and the sensor. Software Sharpness will create an optical illusion of sharpness by increasing the contrast along the edges of shapes within the image. (In-camera or Software processing) Unable to create detail beyond the camera s resolution. It only helps to bring out captured detail.

27 Sharpening

28 Sharpening Sharpening can be applied in the camera or after shooting or both. Very hard to undo over sharpening. Setting the camera s in-camera setting above normal is not recommended. (Advance SLR s) Note: Most compact cameras do not allow you to set sharpening. It is recommended when shooting in JPEG to apply a low or normal in-camera sharpening. RAW images can be sharpened or unsharpened during image processing.

29 Sharpening

30 Image Conversion & Compression Two Types Lossless Conversion: No information is lost in the process. TIFF Lossy Compression: Reduces the file size by discarding information. JPEG

31 Image Conversion & Compression TIFF = Tagged Image File Information Separates the image information into categories and assigns tags for each category.

32 Image Conversion & Compression JPEG = Joint Photographic Experts Group Separates the image into color and detail information. Compresses color information more than detail information. Sorts the detail information into fine and course detail discards the fine detail first because our eyes are more sensitive to course detail

33 Image Compression NUMERICAL EXAMPLES OF FILE SIZES Uncompressed TIFF = 14.1 MB Uncompressed RAW = 7.7 MB 100% Quality JPEG = 2.3 MB 80% Quality JPEG = 1.3 MB 60% Quality JPEG = 0.7 MB 20% Quality JPEG = 0.2 MB

34 Example of Image Compression Uncompressed RAW Image File On Monday the weather was sunny On Tuesday the weather was sunny On Wednesday the weather was sunny On Thursday the weather was sunny On Friday the weather was sunny On Saturday the weather was sunny On Sunday the weather was sunny

35 Example of Image Compression Lossless TIFF Image File 1 Mon Lookup Table 1 Tues Wednes whereby 1 = On 1 Thurs day 1 Fri = the weather was 1 Satur = sunny 1 Sun = rainy

36 Example of Image Compression Lossy JPEG Image File Last week the weather was mostly sunny

37 Example of File Formats & Image Compression Uncompressed RAW Image File On Monday the weather was sunny On Tuesday the weather was sunny On Wednesday the weather was sunny On Thursday the weather was sunny On Friday the weather was sunny On Saturday the weather was sunny On Sunday the weather was sunny Lossless TIFF Image File 1 Mon Lookup Table 1 Tues Wednes whereby 1 = On 1 Thurs day 1 Fri = the weather was 1 Satur = sunny 1 Sun = rainy Lossy JPEG Image File Last week the weather was mostly sunny