The Digital Image Pipeline
Written by Abin Alex and Anu Joseph.
Abstract
The digital image pipeline turns light into a file in four steps: sensor readout, analogue-to-digital conversion, processing and saving. This guide explains each step and the meaning of bit depth. It distinguishes the RAW file, which keeps the sensor data with little processing, from the JPEG file, which is processed and compressed in the camera, and it outlines other file types and how to choose between them. It closes with the changes AI brings to the pipeline. It is written for photographers and cinematographers.
Keywords: digital image pipeline; RAW; JPEG; bit depth; analogue-to-digital conversion
What happens between the sensor and the file?
Short answer. The sensor reads out an analogue signal, a converter turns it into numbers, the processor builds an image and the camera saves a file (Nakamura, 2006).
- Sensor readout: each photosite holds an electrical charge in proportion to the light it received (Nakamura, 2006).
- Analogue-to-digital conversion (ADC): the charge is converted into a number. The number of bits decides how many tone levels are possible (Nakamura, 2006).
- Image processor: demosaicing builds full colour from the Bayer mosaic, then noise reduction, sharpening and tone mapping follow (Nakamura, 2006) (Bayer, 1976).
- File: the result is saved as RAW, JPEG or HEIF.
- Colour theory such as white balance and colour spaces is covered in Unit III of the course.
| Step | What happens | Output |
|---|---|---|
| 1 Readout | Charge is read from each pixel | Analogue signal |
| 2 ADC | Signal is turned into numbers | Raw digital data |
| 3 Processor | Demosaic, denoise, sharpen, tone map | Image data |
| 4 Save | Data is encoded and stored | RAW, JPEG or HEIF file |
Table 1. The four steps of the digital image pipeline (Nakamura, 2006).
Cham tipLearn the four words: readout, convert, process, save.
Cham taskWrite the four steps on a card and add one setting that affects each step.
Check yourself: What does the ADC do?
It converts the analogue sensor signal into digital numbers.
What is bit depth?
Short answer. Bit depth is the number of bits used to store each colour channel. More bits mean more tone levels and smoother gradients.
- An 8-bit JPEG has 256 tone levels per channel, which gives about 16.8 million colours (256 × 256 × 256).
- A 12-bit RAW file has 4096 levels per channel, which gives about 68.7 billion colours.
- A 14-bit RAW file has 16 384 levels per channel, which gives about 4.4 trillion colours.
- More levels give finer control in editing, especially in skies and shadows, where banding can appear in 8-bit files.
| Bit depth | Levels per channel | Total colours |
|---|---|---|
| 8-bit | 256 | 16.8 million |
| 12-bit | 4096 | 68.7 billion |
| 14-bit | 16 384 | 4.4 trillion |
Table 2. Bit depth and colours. Totals are levels cubed (calculated).
Cham tipBit depth is about smoothness of tone, not about how many colours the eye can name.
Cham taskCalculate the colours for 10-bit video: 1024 × 1024 × 1024.
Check yourself: How many levels does 12-bit give?
4096 levels per channel.
What is the difference between RAW and JPEG?
Short answer. A RAW file holds unprocessed or lightly processed sensor data and needs software before use. A JPEG is processed, compressed and ready to share.
- RAW is called a digital negative. It must be processed in software before it is printed or shared.
- RAW has a wider dynamic range and colour gamut, finer editing control and the option to change the colour space after capture.
- JPEG opens in almost any program, uses compression and records 8 bits per channel, so it has less room for editing.
- RAW files are usually larger than JPEG files because they hold more data. RAW formats differ by manufacturer, so each needs compatible software.
- Many cameras can record both at once, so you can share the JPEG and keep the RAW.
| Point | RAW | JPEG |
|---|---|---|
| Processing | Done later in software | Done in the camera |
| Bit depth | 12 to 14 bit common | 8 bit |
| File size | Larger | Smaller |
| Editing room | High | Limited |
| Ready to share | No | Yes |
Table 3. RAW and JPEG compared.
Cham tipUse RAW when the light is difficult and JPEG when speed matters more than editing.
Cham taskShoot the same scene in RAW and JPEG. Lift the shadows by two stops on both and compare.
Check yourself: Which file type is usually larger, RAW or JPEG?
RAW.
What other image file types are there?
Short answer. Image file types differ in how they compress data. Some lose data and some keep it exactly.
- TIFF is flexible and usually lossless, so files are large.
- PNG is lossless and exactly reversible.
- GIF uses a table of up to 256 colours.
- JPEG is optimised for photographs and reaches high compression.
- BMP is an uncompressed format created by Microsoft.
- A raster image is a grid of pixels. A vector image is stored as lines and curves and can be scaled to any size.
| Type | Compression | Best for |
|---|---|---|
| JPEG | Lossy | Photographs for web and sharing |
| PNG | Lossless | Graphics, screenshots |
| TIFF | Usually lossless | Print and archive |
| GIF | 256 colours | Simple animations |
| Vector (SVG, AI) | Not pixels | Logos, illustrations |
Table 4. Common image file types.
Cham tipLossless means you can recover the original exactly. Lossy means some data is gone for good.
Cham taskSave one photo as JPEG at three quality levels. Compare file sizes and quality.
Check yourself: Is PNG lossy or lossless?
Lossless.
How does AI change the pipeline?
Short answer. AI now helps with noise reduction, upscaling and subject recognition inside the pipeline, and content credentials can sign the result (Lukac, 2011).
- Computational methods can merge frames, reduce noise and recognise subjects before the file is saved (Lukac, 2011).
- AI upscaling creates detail by prediction. It is a guess, not a measurement.
- C2PA content credentials are a technical standard that lets a camera or editor sign the capture and edit history cryptographically.
- Credentials do not prove that a picture is true. They record where the file came from and what was done to it.
- Decide what your work needs: an honest record, or the best-looking result.
Cham tipKnow what your camera does before the file is written.
Cham taskCheck whether your camera or phone offers content credentials. Write what it records.
Check yourself: Does AI upscaling add real detail?
No. It predicts detail, so the added detail is a guess.
Questions beginners ask
What is the digital image pipeline?
It is the chain from sensor readout and analogue-to-digital conversion to processing and saving the file.
What is bit depth?
Bit depth is the number of bits used for each colour channel. 8-bit has 256 levels, 12-bit has 4096 and 14-bit has 16 384.
What is a RAW file?
A RAW file holds unprocessed or lightly processed sensor data. It needs software to process it before use.
Is RAW better than JPEG?
RAW gives more editing room. JPEG is smaller and ready to share. The better choice depends on the job.
Are RAW files bigger than JPEG?
Usually yes, because RAW holds more data and JPEG is compressed.
What are C2PA content credentials?
They are a technical standard that records and signs where a file came from and how it was edited.
References
- Bayer, B.E. (1976) Color imaging array. US Patent 3,971,065. Washington, DC: US Patent and Trademark Office.
- Lukac, R. (ed.) (2011) Computational Photography: Methods and Applications. Boca Raton: CRC Press.
- Nakamura, J. (ed.) (2006) Image Sensors and Signal Processing for Digital Still Cameras. Boca Raton: CRC Press.
How to cite this guide. Alex, A., & Joseph, A. (2026). Digital image pipeline: A guide for photographers and cinematographers. Creative Hut Academy. https://creativehut.org/library/digital-image-pipeline/
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