WO2013160524A1

WO2013160524A1 - Imaging

Info

Publication number: WO2013160524A1
Application number: PCT/FI2012/050410
Authority: WO
Inventors: Mikko Muukki; Tomi Sokeila
Original assignee: Nokia Corporation
Priority date: 2012-04-25
Filing date: 2012-04-25
Publication date: 2013-10-31

Abstract

A method, apparatus and computer program are provided for choosing the best image of multiple images that have been captured using a burst capture mode of a digital camera. The method comprises: storing a series of images in a buffer (301 ) over a period of time; analyzing at least some of the images in the buffer (302), or derivatives of at least some of the images in the buffer, during the period of time in order to identify at least one image having at least one particular characteristic; and deciding to keep the at least one image (303), in response to identifying that the at least one image has the at least one particular characteristic. The particular characteristics may relate to the sharpness or brightness of the image, or the presence of an object or a person in the image.

Description

TITLE

Imaging

TECHNOLOGICAL FIELD

Embodiments of the present invention relate to imaging. In particular, they relate to imaging using a buffer.

BACKGROUND

Capturing the right image at the right moment using a camera can, at times, be difficult. Some cameras have a burst capture mode in which they capture a series of images sequentially, for example, at 2 to 60 frames per second. However, use of a burst capture mode can lead to a large number of images being stored in a camera's memory. It may take a long period of time for a user to assess the images and determine which images he wishes to keep, and which he wishes to discard.

BRIEF SUMMARY According to various, but not necessarily all, embodiments of the invention there is provided a method, comprising: storing a series of images in a buffer over a period of time; analyzing at least some of the images in the buffer, or derivatives of at least some of the images in the buffer, during the period of time in order to identify at least one image having at least one particular characteristic; and deciding to keep the at least one image, in response to identifying that the at least one image has the at least one particular characteristic.

According to various, but not necessarily all, embodiments of the invention there is provided an apparatus, comprising: at least one processor; and at least one memory storing computer program instructions configured, working with the at least one processor, to cause the apparatus to perform at least the following: storing a series of images in a buffer over a period of time; analyzing at least some of the images in the buffer, or derivatives of at least some of the images in the buffer, during the period of time in order to identify at least one image having at least one particular characteristic; and deciding to keep the at least one image, in response to identifying that the at least one image has the at least one particular characteristic

According to various, but not necessarily all, embodiments of the invention there is provided a non-transitory computer readable medium storing a computer program comprising computer program instructions configured, working with at least one processor, to cause the following to be performed: storing a series of images in a buffer over a period of time; analyzing at least some of the images in the buffer, or derivatives of at least some of the images in the buffer, during the period of time in order to identify at least one image having at least one particular characteristic; and deciding to keep the at least one image, in response to identifying that the at least one image has the at least one particular characteristic. According to various, but not necessarily all, embodiments of the invention there is provided an apparatus, comprising: means for storing a series of images in a buffer over a period of time; means for analyzing at least some of the images in the buffer, or derivatives of at least some of the images in the buffer, during the period of time in order to identify at least one image having at least one particular characteristic; and means for deciding to keep the at least one image, in response to identifying that the at least one image has the at least one particular characteristic.

According to various, but not necessarily all, embodiments of the invention there is provided an apparatus, comprising: at least one processor; and at least one memory storing computer program instructions configured, when working with the at least one processor, to cause the apparatus to perform at least the following: storing a series of images in a buffer; analyzing at least some of the images in the buffer, or derivatives of at least some of the images in the buffer, in order to identify at least one image having at least one particular characteristic; and deciding to keep the at least one image, in response to identifying that the at least one image has the at least one particular characteristic.

BRIEF DESCRIPTION

For a better understanding of various examples of embodiments of the present invention reference will now be made by way of example only to the accompanying drawings in which: Fig. 1 illustrates a first apparatus;

Fig. 2 illustrates a second apparatus;

Fig. 3 illustrates a flow chart of a method; and

Fig. 4 illustrates a series of images. DETAILED DESCRIPTION

Embodiments of the invention involve buffering captured images and analyzing the images while the buffering is on-going. If the analysis reveals that a buffered image has one or more desirable characteristics, the buffered image is kept.

The Figures illustrate an apparatus 10, comprising: at least one processor 12; and at least one memory 14 storing computer program instructions 18 configured, working with the at least one processor 12, to cause the apparatus 10 to perform at least the following: storing a series of images 100 in a buffer 26 over a period of time; analyzing at least some of the images in the buffer 26, or derivatives of at least some of the images in the buffer 26, during the period of time in order to identify at least one image having at least one particular characteristic; and deciding to keep the at least one image, in response to identifying that the at least one image has the at least one particular characteristic. Fig. 1 illustrates a schematic of an apparatus 10 comprising at least one processor 12 and at least one memory 14. The apparatus 10 may, for example, be a chip or a chipset. Although a single processor 12 and a single memory 14 are illustrated in Fig. 1 , in some implementations of the invention more than one processor 12 and/or more than one memory 14 is provided. The processor 12 is configured to read from and write to the memory 14. The processor 12 may also comprise an output interface via which data and/or commands are output by the processor 12 and an input interface via which data and/or commands are input to the processor 12.

Although the memory 14 is illustrated as a single component it may be implemented as one or more separate components some or all of which may be integrated/removable and/or may provide permanent/semi-permanent/dynamic/cached storage.

The memory 14 stores a computer program 16 comprising computer program instructions 18 that control the operation of the apparatus 10 when loaded into the processor 12. The computer program instructions 18 provide the logic and routines that enables the apparatus 10/20 to perform the methods illustrated in Fig. 3. The processor 12, by reading the memory 14, is able to load and execute the computer program instructions 18.

The computer program instructions 18 may arrive at the apparatus 10/20 via any suitable delivery mechanism 40. The delivery mechanism 40 may be, for example, a non-transitory computer-readable storage medium, a computer program product, a memory device, a record medium such as a compact disc read-only memory (CD-ROM) or digital versatile disc (DVD), and/or an article of manufacture that tangibly embodies the computer program instructions 18. The delivery mechanism 40 may be a signal configured to reliably transfer the computer program instructions 18. The apparatus 10/20 may propagate or transmit the computer program instructions 18 as a computer data signal.

Fig. 2 illustrates a further apparatus 20. The apparatus 20 may, for example, be a camera. In some embodiments of the invention, the apparatus 20 may be hand portable and may have further functionality. For example, the apparatus 20 may be configured to operate as a mobile telephone, a tablet computer, a games console and/or a portable music player.

The apparatus 20 comprises an image sensor 22, an image signal processor 24, a buffer 26, a non-volatile memory 28, a display 29 and the apparatus 10 illustrated in Fig 1. The elements 12, 14, 22, 24, 26, 28 and 29 are operationally coupled and any number or combination of intervening elements can exist (including no intervening elements).

The processor 12 is configured to read from the buffer 26 and may also be configured to write to the buffer 26. The buffer 26 may, for example, be a first-in first-out (FIFO) buffer such as circular/ring buffer.

The processor 12 is configured to read from the non-volatile memory 28 and to write to the nonvolatile memory 28. The non-volatile memory 28 may be any type of non-volatile memory. It may, for example, be flash memory. The non-volatile memory 28 may be fixed in place in the apparatus (as "internal memory") or removable (for example, it may be provided in a removable memory card).

The display 29 may be any type of display. It may, for example, be a liquid crystal display (LCD), an organic light emitting diode (OLED) display or a quantum dot display.

The image sensor 22 is configured to capture images by converting incident light into electronic images. The electronic images produced by the image sensor may, for example, be in Bayer format. The image sensor 22 may, for example, be a charge coupled device (CCD), a complementary metal-oxide-semiconductor (CMOS) sensor or any other type of image sensor.

The image signal processor 24 is configured to process the images produced by the image sensor 22. In this example, the image signal processor 24 receives images from the image sensor 22 as an input and outputs two versions of each input image: a higher resolution version and a lower resolution version. The lower resolution version is effectively a derivative of the higher resolution image and is made up of fewer pixels than the higher resolution image. The derivatives may, for example, be compressed versions of the higher resolution images and/or crops of the higher resolution images. The high and low resolution images output by the image signal processor 24 may be in YUV (luminance-bandwidth-chrominance) format.

In some implementations, the higher resolution images output by the image signal processor 24 have a resolution of at least 2 megapixels. In other implementations, they have a resolution of at least 5 megapixels. The higher resolution images may or may not correspond with a maximum resolution of the image sensor 22 for a particular aspect ratio. Different aspect ratios (for example, 4:3 and 16:9) may have different maximum resolutions. In the Fig. 2 example, the image signal processor 24 is configured to store the higher resolution images in the buffer 26.

The low resolution/derivative images are provided to the processor 12 in the Fig. 2 example. The processor 12 outputs the derivatives to the display 29, in order to enable the display 29 to act as a camera viewfinder. The derivatives may, for example, have a resolution that corresponds with the resolution of the display 29 (for instance, 1280 x 720). The processor 12 may output multiple derivative frames per second to the display 29 to enable the display 29 to act as a viewfinder. In the Fig. 2 example, the processor 12 is configured to analyze the low resolution/derivative images that are output by the image signal processor 24 to determine whether each derivative image has one or more particular characteristics. Analyzing the low resolution derivatives has the potential advantage of being quicker and/or requiring fewer processing resources than analyzing high resolution images (for example, of 5 megapixels or more).

While the processor 12 is analyzing a derivative image, the high resolution image from which the derivative image was derived is stored in the buffer 26. If the processor 12 determines that the derivative image has one or more particular characteristics, it decides to keep the high resolution image stored in the buffer 26 (which corresponds with the derivative image) and stores it in the non-volatile memory 28. The high resolution image may be further processed before it is stored. For example, noise filtering may be performed on the high resolution image and/or the high resolution image may be converted into an alternative format.

A method according to embodiments of the invention will now be described in relation to Figs 3 and 4. In this method, a user may initiate image capture by providing an appropriate input to the apparatus 20. The input may, for example, be provided via a touch sensitive display (for instance the display 29) or a depressible key.

The processor 12 responds to the user input by causing the image sensor 22 to begin capturing images (for example, by activating a mechanical shutter or an electronic shutter). At block 301 of Fig. 3, the processor 12 begins storing a series of images in the buffer 26 over a period of time. Images may be stored in the buffer 26 periodically (for example, at between 2 to 60 frames per second). If the buffer 26 becomes full, a newly captured image replaces the oldest image in the buffer 26.

At block 302 of Fig. 3, the processor 12 analyzes at least some of the images in the buffer 26, or derivatives of at least some of the images in the buffer 26, during the period of time in order to identify at least one image having at least one particular characteristic. In this implementation, when an image is captured by the image sensor 22, it provides a high resolution image to the image signal processor 24 in Bayer format. The image signal processor 24 processes the high resolution image and outputs: i) a high resolution image in YUV format, which is stored in the buffer 26, and ii) a derivative of the high resolution image, of a lower resolution, to the processor 12. In a first example of the method illustrated in Fig. 3, a single high resolution image is stored in the buffer 26 at a time. The processor 12 analyzes the derivative image while the high resolution image is stored in the buffer 26 and while the buffering operation that began in block 301 is ongoing. The processor 12 analyzes the derivative image to determine whether it has one or more particular characteristics. For example, the processor 12 may analyze the derivative image to determine: whether it has a brightness above a certain threshold, whether it has a particular sharpness, whether a subject (such as a person or an object) is in the derivative image, whether a subject is in a particular region of the derivative image, whether a person in the image is performing a particular gesture in the derivative image, whether a person is smiling in the derivative image, and/or whether a person's eyes are open in the derivative image.

If the derivative image does not have the one or more particular characteristics, the processor 12 decides not to keep the high resolution image in the buffer 26. If this is the case, the high resolution image may eventually be overwritten with a new high-resolution image during the on- going buffering process.

At block 303 of Fig. 3, once the processor 12 has identified a derivative image having the one or more particular characteristics, it decides to keep its corresponding high resolution image which is stored in the buffer 26. The processor 12 then stores that high resolution image in the non- volatile memory 28. The high resolution image may be further processed by the processor 12 prior to being stored. For example, noise filtering may be performed on the high resolution image and/or the high resolution image may be converted into an alternative format such as a JPEG (Joint Photographic Experts Group) format, a JPEG-XR format, a digital negative (DNG) format, a portable network graphics (PNG) format, a tagged image file format (TIFF), or an RGB (red, green, blue) format.

Once the processor 12 has decided to keep an image, it might allow the buffering process to continue in order to find another image to keep, or it might control the image signal processor 24 to cease storing images in the buffer 26.

Embodiments of the invention advantageously enable a user to capture a scene at the most desirable point in time, without requiring a large amount of skill, and without requiring lots of images to be captured and stored (for example, as in a burst capture mode). For instance, embodiments of the invention may be used to mitigate the amount of blur in an image, or to avoid having an image of a person in which the person's eyes are closed.

A second example of the method illustrated in Fig. 3 differs from the first example in that multiple high resolution images are stored in the buffer 26 at a time. In the second example, the analysis of the derivative images performed by the processor 12 may or may not comprise comparing derivative images with one another to determine whether a particular derivative image has one or more particular characteristics (for example, to determine the best image).

Fig. 4 relates to a possible use case for the second example of the method. Fig. 4 illustrates a series of images 100 that are captured by the apparatus 20 during a firework display. The user wishes to capture the firework display when it is at its brightest. In this use case, the buffer 26 only stores a small number of high resolution images (such as two) at a time. Analysis of the derivative images in this use case comprises comparing the brightness of one derivative image with the brightness of another derivative image.

The image sensor 22 begins to capture images periodically. High resolution Image A is the first image to be captured and stored in the buffer 26, and is soon followed by high resolution Image B. When Image A and Image B are stored in the buffer 26, the processor 12 compares the brightness of derivative of Image B with the brightness of the derivative of Image A.

It is not necessary for the derivatives of both images stored/buffered when the comparison is made. For example, the processor 12 may analyze the derivative of Image A and temporarily store one or more values (in this instance, a brightness value) for the derivative of Image A. The derivative of Image A may be discarded by the processor 12 prior to analyzing the derivative of Image B. When comparing the brightness of the derivative of Image B with that of the derivative of Image A, the processor 12 may merely use the temporarily stored value for Image A.

The processor 12 determines from its analysis that the derivative of Image B is brighter than the derivative of Image A. However, that does not prompt the processor 12 in this example to decide to store (high resolution) Image B in the non-volatile memory 28.

Capture and buffering of the images continues, and when a third image (Image C) is captured, since only two high resolution images can be stored in the buffer 26 at a time, the image signal processor 24 overwrites Image A (the oldest image in the buffer 26) with Image C. The image signal processor 24 also provides a low resolution derivative of Image C to the processor 12 which compares the brightness of that with the brightness of the derivative of Image B. The processor 12 determines from its analysis that the derivative of Image C is brighter than the derivative of Image B. This process continues until Image F is captured and stored in the buffer 26 alongside Image E. The images in the sequence 100 become progressively brighter until Image F, when is darker than Image E. When the derivative of Image F is analyzed and its brightness is compared with that of the derivative of Image E, the processor 12 determines that the derivative of Image F has a lower brightness. The processor 12 concludes that (high resolution) Image E is likely to be brightest image in the sequence 100, and decides to keep (high resolution) Image E. The processor 12 stores Image E in the non-volatile memory 28. Then the processor 12 may allow the image signal processor 24 to continue storing images in the buffer 26 to enable the processor 12 to try to find another image to keep, or it may control the image signal processor 24 to cease the storing images in the buffer 26.

If the speed at which the image analysis is performed by the processor 12 is variable, it may be desirable to store more than two images in the buffer 26 at a time, and to store multiple derivatives of the images in the buffer 26 at a time. The buffering of the derivative images may be used to manage the fluctuations in the speed of the analysis of the derivative images.

The analysis of the derivative images need not involve comparing them with one another to determine which high resolution image is the brightest. The derivative images may be compared, for instance, to determine which high resolution image is the sharpest image in a sequence. In another implementation where images of a moving subject (such as a person or an object) are captured, the comparison may be made to determine which high resolution image or images include the subject within a particular region of interest (for example, in the center of an image).

In some implementations of the invention, the processor 12 may decide to keep multiple high resolution images. The processor 12 may combine the content of those images into a single high resolution image. In order to select images that are suitable for combination, the processor 12 may decide to keep a high resolution image when a subject in motion (such as an object or a person) has moved by at least a threshold distance relative to a prior kept image (for example, such that there is no overlap in the position of the subject when the two images are compared with one another).

The content of the high resolution images which the processor 12 has chosen to keep may then be combined by including the subject multiple times in a single, combined image to show the subject in motion (which could, for example, be a moving skateboarder).

Alternatively, multiple high resolution images may be combined in a single, combined image by removing the subject that was moving from one of the high resolution images by replacing it with background content from one or more of the other high resolution images. Buffering of the high resolution images may be stopped automatically (that is, without user intervention) by the processor 12 when appropriate images have been identified and kept by the processor 12 to form the combined image.

References to 'computer-readable storage medium', 'computer program product', 'tangibly embodied computer program' etc. or a 'controller', 'computer', 'processor' etc. should be understood to encompass not only computers having different architectures such as single /multi-processor architectures and sequential (Von Neumann)/parallel architectures but also specialized circuits such as field-programmable gate arrays (FPGA), application specific circuits (ASIC), signal processing devices and other processing circuitry. References to computer program, instructions, code etc. should be understood to encompass software for a programmable processor or firmware such as, for example, the programmable content of a hardware device whether instructions for a processor, or configuration settings for a fixed- function device, gate array or programmable logic device etc. As used in this application, the term 'circuitry' refers to all of the following:

(a) hardware-only circuit implementations (such as implementations in only analog and/or digital circuitry) and

(b) to combinations of circuits and software (and/or firmware), such as (as applicable): (i) to a combination of processor(s) or (ii) to portions of processor(s)/software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and

(c) to circuits, such as a microprocessor(s) or a portion of a microprocessor(s), that require software or firmware for operation, even if the software or firmware is not physically present. This definition of 'circuitry' applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term "circuitry" would also cover an implementation of merely a processor (or multiple processors) or portion of a processor and its (or their) accompanying software and/or firmware. The term "circuitry" would also cover, for example and if applicable to the particular claim element, a baseband integrated circuit or applications processor integrated circuit for a mobile phone or a similar integrated circuit in server, a cellular network device, or other network device.

The blocks illustrated in Fig. 3. may represent steps in a method and/or sections of code in the computer program 16. The illustration of a particular order to the blocks does not necessarily imply that there is a required or preferred order for the blocks and the order and arrangement of the block may be varied. Furthermore, it may be possible for some blocks to be omitted.

Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed. For example, in some embodiments of the invention, the image signal processor 24 may provide a different number of outputs to those illustrated in Fig. 2. For instance, the image signal processor 24 may only output high resolution images which are analyzed by the processor 12 (rather than derivatives of the high resolution images) to identify at least one image to keep having at least one particular characteristic. The high resolution images may have a resolution of at least 2 megapixels or at least 5 megapixels. The high resolution images may have a resolution that corresponds with a maximum resolution of the image sensor 22 for a particular aspect ratio. The high resolution images may be compressed (for example by downscaling and/or subsampling) prior to analysis for example by a central processing unit (CPU), a graphics processing unit (GPU) or by dedicated hardware

In other embodiments, the image signal processor 24 may provide three different outputs: (i) high resolution images, (ii) derivatives of the high resolution images that are analyzed by the processor 12 to identify at least one image to keep having one or more particular characteristics, and (iii) lower resolution images (which may or may not be derivatives of the high resolution images in (i)) that are output to the display 29 to enable the display to act as a viewfinder. In these embodiments, different image streams are output for processor analysis and for the viewfinder.

In some implementations, the image signal processor 24 does not store the high resolution/full- size images in the buffer 25 in YUV format. The image sensor 22 may (for example) stream images to the buffer 25 in a different format such as Bayer format, non-Bayer format (for example, white RGB) or RGB format. The analysis of images may be performed in same format as the buffering format (for example, Bayer format) or a different format, such as YUV format. If Bayer format images are buffered, image signal processing may convert the high resolution image to alternative format such as JPEG, JPEG-XR, RGB, YUV, DNG, PNG or TIFF before storing in the non-volatile memory 28. In some implementations, the high resolution images that are stored in the buffer 26 may be in a compressed format such as a JPEG format.

Different buffering approaches may be used. For example, in some cases all of the high resolution images output by the image signal processor 24 over a given period of time may be buffered. In other cases, a subset of the high resolution images output by the image signal processor 24 may be buffered.

In some implementations, the image sensor 22 may output the high resolution images and the derivatives of the images.

Features described in the preceding description may be used in combinations other than the combinations explicitly described. Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not. Whilst endeavoring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

I/we claim:

Claims

1 . A method, comprising:

storing a series of images in a buffer over a period of time;

analyzing at least some of the images in the buffer, or derivatives of at least some of the images in the buffer, during the period of time in order to identify at least one image having at least one particular characteristic; and

deciding to keep the at least one image, in response to identifying that the at least one image has the at least one particular characteristic.

2. A method as claimed in claim 1 , wherein a single image in the buffer, or a single derivative of an image in the buffer, is analyzed at a time.

3. A method as claimed in claim 1 or 2, wherein analyzing at least some of the images in the buffer, or derivatives of some of the images in the buffer, comprises: comparing at least some of the images in the buffer with one another, or comparing derivatives of at least some of the images in the buffer with one another, during the period of time in order to identify at least one image having at least one particular characteristic.

4. A method as claimed in claim 1 , 2, or 3 wherein the images stored in the buffer have a resolution corresponding with a maximum resolution of the image sensor for a particular aspect ratio.

5. A method as claimed in any of the preceding claims, wherein derivatives of at least some of the images in the buffer are analyzed during the period of time, wherein each derivative is of a lower resolution than its corresponding image in the buffer.

6. A method as claimed in claim 5, wherein the derivatives of the images are output to a display to enable the display to act as a camera viewfinder.

7. A method as claimed in claim 5 or 6, wherein the derivatives of the images are stored in a buffer for analysis during the first period of time.

8. A method as claimed in claim 7, wherein multiple derivatives of the images are stored in the buffer at a particular instance in time.

9. A method as claimed in any of the preceding claims, wherein multiple images are stored in the buffer at a particular instance in time.

10. A method as claimed in any of the preceding claims, wherein after deciding to keep the at least one image, the at least one image is further processed prior to being stored.

1 1 . A method as claimed in any of the preceding claims, further comprising: ceasing to store images in the buffer after deciding to keep the at least one image.

12. A computer program comprising computer program instructions that, when run on at least one processor, cause the method as claimed in any of claims 1 to 1 1 to be performed.

13. An apparatus comprising means for performing the method as claimed in one or more of claims 1 to 1 1.

14. An apparatus, comprising:

at least one processor; and

at least one memory storing computer program instructions configured, working with the at least one processor, to cause the apparatus to perform at least the following:

storing a series of images in a buffer over a period of time;

15. An apparatus as claimed in claim 14, wherein a single image in the buffer, or a single derivative of an image in the buffer, is analyzed at a time.

16. An apparatus as claimed in claim 14 or 15, wherein analyzing at least some of the images in the buffer, or derivatives of some of the images in the buffer, comprises: comparing at least some of the images in the buffer with one another, or comparing derivatives of at least some of the images in the buffer with one another, during the period of time in order to identify at least one image having at least one particular characteristic.

17. An apparatus as claimed in claim 14, 15, or 16 wherein the images stored in the buffer have a resolution corresponding with a maximum resolution of the image sensor for a particular aspect ratio.

18. An apparatus as claimed in any of claims 14 to 17, wherein derivatives of at least some of the images in the buffer are analyzed during the period of time, wherein each derivative is of a lower resolution than its corresponding image in the buffer.

19. An apparatus as claimed in claim 18, wherein the derivatives of the images are output to a display to enable the display to act as a camera viewfinder.

20. An apparatus as claimed in claim 18 or 19, wherein the derivatives of the images are stored in a buffer for analysis during the first period of time.

21 . An apparatus as claimed in claim 20, wherein multiple derivatives of the images are stored in the buffer at a particular instance in time.

22. An apparatus as claimed in any of claims 14 to 21 , wherein multiple images are stored in the buffer at a particular instance in time.

23. An apparatus as claimed in any of claims 14 to 22, wherein the computer program instructions are configured, working with the at least one processor, to cause the apparatus to perform: after deciding to keep the at least one image, the at least one image is further processed prior to being stored.

24. An apparatus as claimed in any of claims 14 to 23, wherein the computer program instructions are configured, working with the at least one processor, to cause the apparatus to perform: ceasing to store images in the buffer after deciding to keep the at least one image.

25. A non-transitory computer readable medium storing a computer program comprising computer program instructions configured, working with at least one processor, to cause the following to be performed:

storing a series of images in a buffer over a period of time;

26. A non-transitory computer readable medium as claimed in claim 25, wherein a single image in the buffer, or a single derivative of an image in the buffer, is analyzed at a time.

27. A non-transitory computer readable medium as claimed in claim 25 or 26, wherein analyzing at least some of the images in the buffer, or derivatives of some of the images in the buffer, comprises: comparing at least some of the images in the buffer with one another, or comparing derivatives of at least some of the images in the buffer with one another, during the period of time in order to identify at least one image having at least one particular characteristic.

28. A non-transitory computer readable medium as claimed in claim 25, 26, or 27 wherein the images stored in the buffer have a resolution corresponding with a maximum resolution of the image sensor for a particular aspect ratio.

29. An apparatus, comprising:

means for storing a series of images in a buffer over a period of time;

means for analyzing at least some of the images in the buffer, or derivatives of at least some of the images in the buffer, during the period of time in order to identify at least one image having at least one particular characteristic; and

means for deciding to keep the at least one image, in response to identifying that the at least one image has the at least one particular characteristic.

30. An apparatus as claimed in claim 29, wherein analyzing at least some of the images in the buffer, or derivatives of some of the images in the buffer, comprises: comparing at least some of the images in the buffer with one another, or comparing derivatives of at least some of the images in the buffer with one another, during the period of time in order to identify at least one image having at least one particular characteristic.