Image evaluation method, image capturing method and digital camera thereof for evaluating and capturing images according to composition of the images

An image evaluation method for a digital camera includes analyzing the composition of an image for obtaining a characteristic of the composition of the image, computing an ideal characteristic value, a real characteristic value, and a difference value between the ideal characteristic value and the real characteristic value, and generating a grade according to the difference value to show quality related to the composition of the image.

BACKGROUND OF THE INVENTION

The present invention relates to an image evaluation method, an image capturing method and a digital camera system thereof, and more particularly, to an image evaluation method for analyzing the composition of an image and generating a grade displayed to a photographer accordingly.

With the progress of semiconductor and image processing technologies, in recent year, digital still/video cameras have become popular and are often incorporated into portable devices, such as mobile phones and personal digital assistants. Digital cameras are developed toward higher resolution, powerful image processing capability, and user-friendly control interface. For example, a digital camera has different scene modes, such as portrait, landscape, night scene, etc., and captures a picture with a predetermined parameter setting of a chosen mode. The predetermine parameter setting is used to adjust parameters of the digital camera such as shutter speed and aperture to suit the chosen mode. Benefited from these advancements, people use digital still/video cameras more conveniently and take a photograph that meets basic image quality.

However, an image with low noise and high resolution does not intend that it is a good image if the composition of the image is bad. The image composition is a key to an interesting image, which concerns about the proportion of a main object to the entire image, relative sizes of objects, positions of the objects, and many other factors. For an ordinary photographer who is not skilled in photography, it is difficult to arrange objects in an impressive composition; at the same time, the photographer usually changes the zooming parameter and camera location at random before the image is actually captured, which is also called a “preview mode”. As a result, the composition of the captured image is typically not very impressive.

SUMMARY OF THE INVENTION

It is therefore a primary objective of the claimed invention to provide an image evaluation method, an image capturing method and a digital camera thereof.

According to an embodiment of the present invention, an image evaluation method for a digital camera is disclosed. The image evaluation method comprises: analyzing the composition of an image for obtaining a characteristic of the composition of the image; computing an ideal characteristic value, a real characteristic value, and a difference value between the ideal characteristic value and the real characteristic value; and generating a grade according to the difference value to show quality related to the composition of the image.

According to an embodiment of the present invention, an image capturing method for a digital camera is disclosed. The image capturing method comprises: receiving an image; performing an image evaluation process on the image, for generating a grade related to the composition of the image; outputting the image and the grade; and capturing the image.

According to an embodiment of the present invention, a digital camera is disclosed. The digital camera comprises an image capturing unit, a display unit, and a signal processing unit. The image capturing unit is utilized for receiving an image and capturing the image. The display unit is utilized for displaying the image and a grade related to quality of the composition of the image. The signal processing unit is coupled to the image capturing unit and the display unit, and is utilized for performing an image evaluation process on the image, for generating the grade as a reference.

DETAILED DESCRIPTION

There are some image composition techniques implemented in digital cameras to assist photographers taking pictures with better composition. One is showing composition guides on an LCD screen, such as thirds rule, diagonal rule or 3-by-3 grids; the photographer has to manually select guides fitting the scene to be captured. Another technique automatically detects and focuses on a face image, and applies an auto editing function after photo taking, for example, to trim the photo so that the detected face is positioned at an appropriate position with an appropriate proportion.

Please refer toFIG. 1, which is a flowchart of an image evaluation method10according to an embodiment of the present invention. The image evaluation method10generates a grade reflecting the composition of an image. The image evaluation method10comprises the following steps:

Step102: Analyze the composition of an image for obtaining a characteristic of the composition of the image.

Step104: Compute an ideal characteristic value, a real characteristic value, and a difference value between the ideal characteristic value and the real characteristic value.

Step106: Generate a grade displayed to a photographer according to the difference value to show quality related to the composition of the image.

For a digital camera, the image evaluation method10can be performed on a preview image in a preview mode before an image is actually taken or on a captured image. First in Step102, the image evaluation method10analyzes an image to locate components in the image, such as grass, sky, ocean, and/or objects in the image, such as human being, animal, so as to obtain a characteristic of the composition of the image. The characteristic of the composition depends on the components and/or objects in the image, which reflects a major consideration when composing the image. For example, if the image is a scenery image mainly composed of grass and sky, the characteristic of the composition may be the proportion of grass to sky, which makes the horizon in the image. If the image illustrates a rabbit in the grass, the characteristic of the composition of the image may be the position of the main object, the rabbit. Please note that, the quantity of the obtained characteristics of the composition is not limited in the embodiment of the present invention; for example, if there are two persons in the scenery image exampled previously, the image evaluation method10obtains one more characteristic, such as the scale.

Next, in Step104, the image evaluation method10computes an ideal characteristic value of the obtained characteristic corresponding to the best composition for the image, a real characteristic value of the obtained characteristic corresponding to current composition, and a difference value between the ideal characteristic value and the real characteristic value. A smaller difference value indicates a better composition. In Step106, the image evaluation method10generates a grade according to the difference value. The grade relates to the composition of the image and is displayed either during the preview mode or after an image is captured, so the photographer has knowledge on whether the image is worth capturing during the preview mode or whether the image needs to be recaptured if the grade is given after capture. For example, the grade is displayed on an LCD screen of the digital camera and is inversely proportional to the difference value between the ideal and the real characteristic values.

If the image evaluation method is activated in the preview mode, the photographer can try various compositions by zoom in or zoom out, or by moving the camera up, down, left, or right, or the photographer can even move to some other positions. The instant grade helps the photographer to take photos with better composition.

If the image evaluation method is performed after a picture is captured, the grade can be stored along with the picture. The grade is an indication for the photographer to determine if he/she needs to take another picture. The grade can be used for photo management, for example, sorting pictures according to the grade, so those with lower grade can be deleted first, especially when there are only a few memory spaces left.

Please refer toFIG. 2andFIG. 3, which illustrate an image20and an image30displayed on an LCD of a digital camera. As shown inFIG. 2, the composition of a rabbit positioning in the middle of the grass is a little dull. The image evaluation method10first analyzes the image20and obtains that the characteristic of the composition is the position of the main object, which is a rabbit, and computes the ideal position of the rabbit (x0, y0), the real position of the rabbit (xc, xc), and the difference value equal to √{square root over ((xc−x0)2+(yc−y0)2)}{square root over ((xc−x0)2+(yc−y0)2)}. The image evaluation method10generates a grade reflecting the difference value, for example, a grade “5” relative to the highest “10”, and displays the grade with the image20on the screen. The photographer may wish to change the composition of the image20by moving the digital camera or changing the zooming parameter.

As shown inFIG. 3, the image evaluation method10analyzes the image30and obtains that the characteristic of the composition of the image30is the proportion of main components, which are the mountain and the sky, and computes the ideal proportion of a distance dU0of the upper component to a distance dL0of the lower component, the real proportion of a distance dUCof the upper component to a distance dLCof the lower component, and the difference value equal to (dUC/dLC−dU0/dL0). An exemplary ideal proportion of dU0to dL0is 2/1. The image evaluation method10generates a relatively high grade according to the difference value of the image30. For example, a grade “8” is displayed with the image30so that the photographer knows that the composition is considerably good.

The image evaluation method10can be used in the digital camera in several ways. Please refer toFIG. 4, which is a block diagram of a digital camera40according to an embodiment of the present invention. The digital camera40comprises an image capturing unit400, a signal processing unit402, and a display unit404. The image capturing unit400is composed of lens, color filters and image sensors, which are well-known by those skilled in the art and are not given in detail. The image capturing unit400is utilized for continuously receiving preview images in a preview mode before an image is actually captured and capturing the image.

The signal processing unit402comprises an image analyzing unit410, a computing unit412and a grading unit414, and is utilized for performing an image evaluation process of the image evaluation method10on a received image, for generating a grade related to the composition of the image. The image analyzing unit410is coupled to the image capturing unit400and is utilized for performing Step102, for obtaining the characteristic of the composition. The computing unit412is coupled to the image analyzing unit410, and is utilized for performing Step104. The grading unit414is coupled to the computing unit412and the display unit404, and is utilized for performing Step106, for generating a grade displayed to a photographer according to a difference value generated by the computing unit412. After the grade is generated, the grading unit414outputs the grade to the display unit404.

Simply, the signal processing unit402performs the image evaluation process for evaluating the composition of the image and generating the grade related to the composition, and the photographer can get feedback from the image evaluation function on how the composition of the image is.

The present invention further provides several embodiments of image capturing methods for the digital camera40inFIG. 4based on the image evaluation method10inFIG. 1. Please refer toFIG. 5, which is a flowchart of an image capturing method50according to an embodiment of the present invention. The image capturing method50is executed when the photographer selects an auto-capture mode, and the method comprises the following steps:

Step504: Perform an image evaluation process on the image for generating a grade related to the composition of the image.

Step506: Display the image and the grade.

Step508: Decide whether to capture the image or not according to the grade. If the grade is qualified, perform Step510; otherwise, back to Step502.

Step510: Capture the image.

Before an image is actually captured, the image capturing method50is repeatedly performed on preview images in a preview mode. In the preview mode, the photographer may changes zoom parameters and moves the digital camera40to try different composition on an image subject. First, the image capturing unit400receives an image (which is a preview image), and the signal processing unit402performs the image evaluation process on the image. Note that the image evaluation process includes steps of the image evaluation method10. The image analyzing unit410, the computing unit412and the grading unit414in the signal processing unit402perform the image evaluation process to generate a grade, which is described previously. Next, the display unit404displays the image and the grade; and therefore, in Step508, whether the image is captured is decided according to the grade.

Please note that, the image capturing method50illustrates both manual shooting and automatic shooting, and there are a little difference for performing Step508. As to the manual shooting, Step508intends that the photographer manually decides whether to capture the image or not after the photographer recognizes the grade. If the grade is qualified, which means that the photographer is satisfied with the grade, the photographer may manually push the shutter-release button to control the image capturing unit400to capture the image. If the photographer is not satisfied with the grade, the photographer may change zoom parameters or/and move the digital camera, and the image capturing method50returns to Step502for a next preview image.

As to the automatic shooting, the photographer sets the digital camera40to a specific mode to perform the automatic shooting. When the photographer pushes the shutter-release button, the image capturing method50is initiated. According to Step508, the digital camera40automatically decides whether to capture the image or not depends on a result of comparing the grade and a predetermined threshold corresponding to an acceptable composition. If the grade is qualified, which means that the grade is higher than or equal to the threshold, the image capturing unit400automatically captures the image; otherwise, the image capturing unit400receives a next preview image, as Step502. In a word, by the image capturing method50, the photographer can see the grade shown on the display unit404and know how the composition of the preview image is valued so as to decide whether to capture the image manually, or let the digital camera40automatically captures the image.

From the above, the digital camera40uses the image evaluation method10to generate the grade displayed corresponding to the composition of the preview image, for capturing the image with better composition. However, there is a time interval in which the composition of the image may be changed between when the photographer sees the grade and when the image is actually captured. In another embodiment of the present invention, the digital camera40can also perform the image evaluation method10on the captured image by the image analyzing unit410, the computing unit412and the grading unit414, and generate a grade related to the composition of the captured image, which is called post-evaluation. Therefore, the display unit404displays the grade such that the photographer can know how good the composition of the captured image is.

Note that according to the image evaluation method50, the computing unit412can compute the ideal characteristic value so that information of the ideal composition can also be passed to the photographer during the preview mode. Please refer toFIG. 6, which is a block diagram of a digital camera60according to an embodiment of the present invention. The digital camera60comprises an image capturing unit600, a signal processing unit602and a display unit604. The signal processing unit602comprises an image analyzing unit610, a computing unit612, a grading unit614and an indication unit616. All units and related operations except the indication unit616are similar to those in the digital camera40inFIG. 4and corresponding descriptions are not repeated. The indication unit616is coupled to the computing unit612and the display unit604, and is utilized for generating an indication displayed on the display unit604according to the ideal characteristic value generated by the computing unit612. The display unit604displays the indication to guide the photographer moves the camera or changes the zooming parameter toward the ideal composition. The indication may be an icon displayed on the screen suggesting the photographer to zoom in or zoom out, or to move toward a particular direction. The photographer may follow the icon to compose a picture with better composition. Take theFIG. 2andFIG. 3as examples. If the image20inFIG. 2is a preview image of the digital camera60, there is an arrow which is generated by the indication unit616for indicating the ideal position of the main object. As shown inFIG. 3, there is a guide line generated by the indication unit616for indicating the ideal horizon that helps to achieve the ideal proportion of the upper component to the lower component of the image.

In some embodiments, the image evaluation method only calculates and output the indication instead of the grade. Furthermore, the indication or the grade output from the signal processing unit does not need to be in a display form, for example, it can be a control signal provided to a speaker.

In conclusion, according to embodiments of the present invention, the image evaluation method generates a grade related to the composition of the image, and the image capturing method further uses the image evaluation method to evaluate the composition and decide whether to capture during preview mode or whether to recapture after a picture is captured. Therefore, a digital camera employing the image evaluation method and image capturing method assists the photographer to take photos with better composition in an easy way.