Tag Archives: raw conversion

Pi HQ Cam Sensor Performance

May 17, 2020 Jack 13 Comments

Now that we know how to open 12-bit raw files captured with the new Raspberry Pi High Quality Camera, we can learn a bit more about the capabilities of its 1/2.3″ Sony IMX477 sensor from a keen photographer’s perspective. The subject is a bit dry, so I will give you the summary upfront. These figures were obtained with my HQ module at room temperature and the raspistill – -raw (-r) command:

Raspberry Pi HQ Camera	raspistill --raw -ag 1	Comments
Black Level	256.3 DN	256.0 - 257.3 based on gain
White Level	4095	Constant throughout
Analog Gain	1	Gain Range 1 - 16
Read Noise	3 e-, gain 1 1.5 e-, gain 16	1.53 DN from black frame 11.50 DN
Clipping (FWC)	8180 e-	at base gain, 3400e-/um^2
Dynamic Range	11.15 stops 11.3 stops	SNR = 1 to Clipping Read Noise to Clipping
System Gain	0.47 DN/e-	at base analog gain
Star Eater Algorithm	Partly Defeatable	All channels - from base gain and from min shutter speed
Low Pass Filter	Yes	All channels - from base gain and from min shutter speed

Continue reading Pi HQ Cam Sensor Performance →

Color, IQ, Processing, Sensors

Phase One IQ3 100MP Trichromatic vs Standard Back Linear Color, Part III

January 11, 2018 Jack Leave a comment

Over the last two posts we’ve been exploring some of the differences introduced by tweaks to the Color Filter Array of the Phase One IQ3 100MP Trichromatic Digital Back versus its original incarnation, the Standard Back. Refer to those for the background. In this article we will delve into some of these differences quantitatively^[1].

Let’s start with the compromise color matrices we derived from David Chew’s captures of a ColorChecher 24 in the shade of a sunny November morning in Ohio^[2]. These are the matrices necessary to convert white balanced raw data to the perceptual CIE XYZ color space, where it is said there should be one-to-one correspondence with colors as perceived by humans, and therefore where most measurements are performed. They are optimized for each back in the current conditions but they are not perfect, the reason for the word ‘compromise’ in their name:

Figure 1. Optimized Linear Compromise Color Matrices for the Phase One IQ3 100 MP Standard and Trichromatic Backs under approximately D65 light.

Continue reading Phase One IQ3 100MP Trichromatic vs Standard Back Linear Color, Part III →

ACR, Banding, Color, Exposure, Perceptual, Photometry, Processing

Linear Color: Applying the Forward Matrix

December 12, 2016 Jack Leave a comment

Now that we know how to create a 3×3 linear matrix to convert white balanced and demosaiced raw data into $XYZ_{D50}$ connection space – and where to obtain the 3×3 linear matrix to then convert it to a standard output color space like sRGB – we can take a closer look at the matrices and apply them to a real world capture chosen for its wide range of chromaticities.

Figure 1. Image with color converted using the forward linear matrix discussed in the article.

Continue reading Linear Color: Applying the Forward Matrix →

ACR, Color, LR, Perceptual, Processing

Color: Determining a Forward Matrix for Your Camera

December 7, 2016 Jack 31 Comments

We understand from the previous article that rendering color with Adobe DNG raw conversion essentially means mapping raw data in the form of $rgb$ triplets into a standard color space via a Profile Connection Space in a two step process

$Raw Data \rightarrow XYZ_{D50} \rightarrow RGB_{standard}$

The first step white balances and demosaics the raw data, which at that stage we will refer to as $rgb$ , followed by converting it to $XYZ_{D50}$ Profile Connection Space through linear projection by an unknown ‘Forward Matrix’ (as DNG calls it) of the form

(1) $\begin{equation*} \left[ \begin{array}{c} X_{D50} \\ Y_{D50} \\ Z_{D50} \end{array} \right] = \begin{bmatrix} a_{11} & a_{12} & a_{13} \\ a_{21} & a_{22} & a_{23} \\ a_{31} & a_{32} & a_{33} \end{bmatrix} \left[ \begin{array}{c} r \\ g \\ b \end{array} \right] \end{equation*}$

with data as column-vectors in a 3xN array. Determining the nine $a$ coefficients of this matrix $M$ is the main subject of this article^[1]. Continue reading Color: Determining a Forward Matrix for Your Camera →

adobe camera raw, Color, LR, Processing, Sharpening

How Is a Raw Image Rendered?

October 21, 2016 Jack 19 Comments

What are the basic low level steps involved in raw file conversion? In this article I will discuss what happens under the hood of digital camera raw converters in order to turn raw file data into a viewable image, a process sometimes referred to as ‘rendering’. We will use the following raw capture by a Nikon D610 to show how image information is transformed at every step along the way:

Figure 1. Nikon D610 with AF-S 24-120mm f/4 lens at 24mm f/8 ISO100, minimally rendered from raw by Octave/Matlab following the steps outlined in the article.

Rendering = Raw Conversion + Editing

Continue reading How Is a Raw Image Rendered? →

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