CN104539971A - Inter-viewpoint bit allocation method applied to two-viewpoint video coding - Google Patents

Abstract

Provided is an inter-viewpoint bit allocation method applied to two-viewpoint video coding. Firstly, influences of coding distortion of a basic viewpoint on coding distortion of a non-basic viewpoint are determined, and a rate-distortion model of the basic viewpoint and the non-basic viewpoint is determined; then, an inter-viewpoint bit allocation problem is converted into the problem of minimizing overall coding distortion of the basic viewpoint and the non-basic viewpoint under limited total bit cost condition, the optimal solution is solved, and an optimal inter-viewpoint bit allocation scheme is achieved. The method improves coding efficiency of a multi-viewpoint video, so that quality of the multi-viewpoint video reconstructed at a decoding end is higher under the same coding rate condition, and the method has the advantages of being high in performance and universality and the like, and can be used in coding standards of the multi-viewpoint video.

Description

Bit distribution method between a kind of viewpoint being applied to 2 viewpoint video codings

Technical field

The present invention relates to Bit distribution method between a kind of viewpoint for improving multiple view video coding efficiency, belonging to multiple view video coding mark technical field.

Background technology

Three-dimensional (3D) video, as main video applications in future, refers to that user can enjoy real 3 d video content by 3 D video display device.The correlation technique of 3 D video, such as, the technology such as the display of three-dimensional video acquisition, 3 d video encoding, 3 D video are paid close attention to widely.In order to promote the standardization of 3 D video technology, 2002, Motion Picture Experts Group (Motion Picture Experts Group, and Video Coding Experts group (Video Coding ExpertsGroup MPEG), VCEG) formulated based on multiple view video coding (Multi View Video Coding, MVC) standard (H.264/MVC) H.264.Current MPEG and VCEG formulates MVC standard of new generation, i.e. MV-HEVC based on up-to-date high-performance video coding standard (High EfficiencyVideo Coding, HEVC).In multi-view point video, user can watch the 3 D video of this angle from different angles, user is had incorporate the sense of reality in video scene.Multi-view point video can be widely used in the fields such as broadcast communication, amusement, education, medical treatment and video monitoring.When the more viewpoint of needs, multi-view point video-depth representing 3D scene can be adopted, and adopt 3D-HEVC coding standard to encode; The visual point image that user terminal can adopt View synthesis technology (Depth Image Based Rendering, the DIBR) synthesis based on the degree of depth to need.Therefore, in existing MV-HEVC coding standard framework, the coding structure of 2 viewpoints and 3 viewpoints is only defined.

Between existing multi-view point video, Bit distribution method is the Bit distribution method of fixed proportion, and the coding flow process that fixed proportion bit distributes as shown in Figure 1, adopts the proportionality coefficient preset to be different viewpoint allocation bit.For the video of 2 viewpoints, the bits proportion between BV and NBV can be 2:8,4:6,6:4 etc.; Bits proportion for the video BV of 3 viewpoints and left side not substantially viewpoint (NBVL), right side not substantially viewpoint (NBVR) can be 4:3:3,6:2:2 etc.

The Bit distribution method of fixed proportion does not consider the impact of the coding distortion of BV on the coding distortion of NBV, only arranges a fixing allocation proportion by rule of thumb; Therefore do not possess versatility, the total quality of the multi-view point video of reconstruction is not high yet.From theory analysis, BV has considerable influence to NBV, and the coding distortion of BV can directly propagate in NBV, in the bit allocation procedures therefore between multiple views, should consider the impact of BV on NBV.

Summary of the invention

Bit distribution method for fixed proportion does not possess versatility, the shortcoming that reconstruction video total quality is not high, the present invention is according to basic viewpoint (Base View, BV) to not substantially viewpoint (Non-Base View, NBV) impact, proposes Bit distribution method between a kind of viewpoint being applied to 2 viewpoint video codings.Between the viewpoint of the method concern multi-view point video, bit distributes, determine in multi-view point video, the distortion of basic viewpoint is on the impact of not substantially viewpoint, Bit distribution method between the basic viewpoint of devise optimum and not substantially viewpoint, improve the code efficiency of multi-view point video, make under the condition of same-code code check, the multi-view point video quality that decoding end is rebuild is higher.

Bit distribution method between the viewpoint being applied to 2 viewpoint video codings of the present invention, first determines the impact of the coding distortion of basic viewpoint on the coding distortion of not substantially viewpoint, determines the rate-distortion model of basic viewpoint and not substantially viewpoint; Then, the bit assignment problem between viewpoint is converted under limited total overhead bit condition, minimizes the problem of the binary encoding distortion of basic viewpoint and not substantially viewpoint, and obtain optimal solution (between namely optimum viewpoint bit allocation scheme); Specifically comprise the following steps:

(1) Mathematical Modeling defined between the coding distortion of basic viewpoint and number of coded bits is:

D _bv＝(a _bv·R _bv+b _bv) ^-1,

Wherein, D _bvrepresent the coding distortion of basic viewpoint, R _bvrepresent the number of coded bits of basic viewpoint, a _bvand b _bvfor model parameter, represent R _bvto D _bvinfluence degree; The coding distortion D of not substantially viewpoint _nbvwith the number of coded bits R of not substantially viewpoint _nbvwith the number of coded bits R of basic viewpoint _bvbetween pass be:

D _nbv＝η(a _bvR _bv+b _bv) ^-1+(a _nbvR _nbv+b _nbv) ^-1,

Wherein, η represents that the coding distortion of the basic viewpoint of present frame is to the influence degree of the coding distortion of NBV, a _nbvand b _nbvfor model parameter, represent R _nbvto D _nbvinfluence degree;

η described in step (1) is calculated by following formula:

$\mathrm{\η}=\frac{{\mathrm{Num}}_{\mathrm{PU}\_\mathrm{InterViewSKIPMode}}}{{\mathrm{Num}}_{\mathrm{PU}}},$

Wherein, Num _{pU_InterViewSKIPMode}represent in the not substantially viewpoint of present frame, adopt the quantity of the predicting unit (Prediction Unit, PU) that dancing mode (Inter View SkipMode) is encoded between viewpoint, Num _pUrepresent in the not substantially viewpoint of present frame, the quantity of all predicting unit.

(2) W frame before multi-view video sequences being started most, rate control algorithm is adopted to determine the basic viewpoint of every frame and total bit number of not substantially viewpoint, and be different viewpoint allocation bit by the ratio preset and encode, the coding distortion of the basic viewpoint after coding and number of coded bits are stored in array vector respectively with in, coding distortion and the number of coded bits of not substantially viewpoint are stored in array vector respectively $\stackrel{\→}{D_{\mathrm{nbv}}}=\{D_{\mathrm{nbv},0},...,D_{\mathrm{nbv},W-1}\}$ With $\stackrel{\→}{R_{\mathrm{nbv}}}=\{R_{\mathrm{nbv},0},...,R_{\mathrm{nbv},W-1}\}$ In;

The ratio (initial bit allocation proportion) preset in step (2) is:

(3) according to the distortion of the basic viewpoint in the W frame before present frame with bit number and D in step (1) _bvand R _bvbetween Mathematical Modeling, by linear regression solving equation group:

$\left[\begin{array}{c}{D}_{\mathrm{bv},0}^{-1}\\ \·\\ \·\\ \·\\ \·\\ \·\\ \·\\ D_{\mathrm{bv},W-1}^{-1}\end{array}\right]=a_{\mathrm{bv}}\left[\begin{array}{c}{R}_{\mathrm{bv},0}\\ \·\\ \·\\ \·\\ \·\\ \·\\ \·\\ R_{\mathrm{bv},W-1}\end{array}\right]+b_{\mathrm{bv}},$

Calculate the model parameter a of basic viewpoint _bvand b _bv;

(4) according to the distortion of the not substantially viewpoint in the W frame before present frame with bit number $\stackrel{\→}{R_{\mathrm{nbv}}}=\{R_{\mathrm{nbv},0},...,R_{\mathrm{nbv},W-1}\}$ The bit number of BV $\stackrel{\→}{R_{\mathrm{bv}}}=\{R_{\mathrm{bv},0},...,R_{\mathrm{bv},W-1}\},$ And D in step (1) _nbvwith R _nbvand R _bvbetween Mathematical Modeling, by linear regression solving equation group:

$\left[\begin{array}{c}{(D_{\mathrm{nbv},0}-{\mathrm{\η}}_0{D}_{\mathrm{bv},0})}^{-1}\\ \·\\ \·\\ \·\\ \·\\ \·\\ \·\\ {(D_{\mathrm{nbv},W-1}-{\mathrm{\η}}_{W-1}{D}_{\mathrm{bv},W-1})}^{-1}\end{array}\right]=a_{\mathrm{nbv}}\left[\begin{array}{c}{R}_{\mathrm{nbv},0}\\ \·\\ \·\\ \·\\ \·\\ \·\\ \·\\ R_{\mathrm{nbv},W-1}\end{array}\right]+b_{\mathrm{nbv}},$

Wherein η ₀η _w-1represent that in encoded W frame, in 2 viewpoints of every frame, the distortion of basic viewpoint, to the influence degree of the distortion of not substantially viewpoint, calculates the model parameter a of not substantially viewpoint _nbvand b _nbv;

(5) a of foundation step (3) and step (4) gained _bv, b _bv, a _nbvand b _nbv, and adopt total bit number R of rate control algorithm present frame _c, pass through following formula:

$R_{\mathrm{bv}}=\frac{R_c+\frac{b_{\mathrm{nbv}}}{a_{\mathrm{nbv}}}-\frac{b_{\mathrm{bv}}}{\sqrt{a_{\mathrm{bv}}{a}_{\mathrm{nbv}}(1+\mathrm{\η})}}}{1+\sqrt{\frac{a_{\mathrm{bv}}}{a_{\mathrm{nbv}}(1+\mathrm{\η})}}},$

$R_{\mathrm{nbv}}=\sqrt{\frac{a_{\mathrm{bv}}}{a_{\mathrm{nbv}}(1+\mathrm{\η})}}{R}_{\mathrm{bv}}+\frac{b_{\mathrm{bv}}}{\sqrt{a_{\mathrm{nbv}}{a}_{\mathrm{bv}}(1+\mathrm{\η})}}-\frac{b_{\mathrm{nbv}}}{a_{\mathrm{nbv}}},$

For basic viewpoint and the not substantially viewpoint allocation bit number of present frame, namely calculate the R of present frame _bvand R _nbv;

(6) according to the principle of " first in first out ", by array vector the 0th data delete, and the coding distortion of present frame and number of coded bits are added to the end of array vector, upgrade array vector

(7) return step (3), next frame is encoded.

The present invention mainly improves the code efficiency of multi-view point video, determines the rate-distortion model of multi-view point video, and the basic viewpoint of present frame (comprising multiple visual point image) is on the impact of not substantially viewpoint; Then adopt rate control techniques to calculate the spendable total bit number of present frame, and by optimal method, be basic viewpoint and the not substantially viewpoint allocation bit of every frame, and then improve the code efficiency of multi-view point video.Compared with prior art have the following advantages:

1) the present invention is according to the coding distortion of basic viewpoint on the impact of the coding distortion of not substantially viewpoint, and the Bit distribution method between the multiple views devising distortion performance optimum, improves the code efficiency of multi-view point video;

2) the present invention can adjust bit allocation proportion between viewpoint to any video, has very strong adaptivity.

Accompanying drawing explanation

Fig. 1 is the coding flow chart that fixed proportion bit distributes.

Fig. 2 is the flow chart of Bit distribution method when being applied to 2 viewpoints coding of the present invention.

Fig. 3 be adopt method of the present invention and fixed proportion bit to distribute respectively method to 2 of three-dimensional video sequence Balloons the experimental result that viewpoint is encoded (rate distortion curve) comparison diagrams.

Fig. 4 be adopt method of the present invention and fixed proportion bit to distribute respectively method to 2 of three-dimensional video sequence BookArrival the experimental result that viewpoint is encoded (rate distortion curve) comparison diagrams.

Embodiment

As Fig. 2, Bit distribution method between the viewpoint that the present invention is applied to 2 viewpoint videos coding, detailed process is as follows:

(1) Mathematical Modeling defined between the coding distortion of basic viewpoint (Base View, BV) and number of coded bits is

D _bv＝(a _bv·R _bv+b _bv) ^-1,

Wherein, D _bvrepresent the coding distortion of BV, R _bvrepresent the number of coded bits of BV, a _bvand b _bvfor model parameter, represent R _bvto D _bvinfluence degree; Coding distortion (the D of NBV _nbv) with the number of coded bits (R of NBV _nbv) and the number of coded bits (R of BV _bv) between pass be:

D _nbv＝η(a _bvR _bv+b _bv) ^-1+(a _nbvR _nbv+b _nbv) ^-1,

Wherein, η represents the influence degree of the coding distortion of present frame BV to the coding distortion of NBV, a _nbvand b _nbvfor model parameter, represent R _nbvto D _nbvinfluence degree;

Described η can be calculated by following formula

$\mathrm{\η}=\frac{{\mathrm{Num}}_{\mathrm{PU}\_\mathrm{InterViewSKIPMode}}}{{\mathrm{Num}}_{\mathrm{PU}}},$

Wherein, Num _{pU_InterViewSKIPMode}represent in the NBV of present frame, adopt the quantity of the predicting unit (Prediction Unit, PU) that dancing mode (Inter View Skip Mode) is encoded between viewpoint, Num _pUrepresent in the NBV of present frame, the quantity of all predicting unit.

(2) W frame before multi-view video sequences being started most, rate control algorithm is adopted to determine total bit number of BV and NBV of every frame, and be different viewpoint allocation bit by the ratio preset and encode, the coding distortion of the BV after coding and number of coded bits are stored in array vector respectively $\stackrel{\→}{D_{\mathrm{bv}}}=\{D_{\mathrm{bv},0},...,D_{\mathrm{bv},W-1}\}$ With $\stackrel{\→}{R_{\mathrm{bv}}}=\{R_{\mathrm{bv},0},...,R_{\mathrm{bv},W-1}\}$ In, coding distortion and the number of coded bits of NBV are stored in array vector respectively $\stackrel{\→}{D_{\mathrm{nbv}}}=\{D_{\mathrm{nbv},0},...,D_{\mathrm{nbv},W-1}\}$ With $\stackrel{\→}{R_{\mathrm{nbv}}}=\{R_{\mathrm{nbv},0},...,R_{\mathrm{nbv},W-1}\}$ In;

The described ratio (initial bit allocation proportion) preset is

(3) according to the distortion of the BV in the W frame before present frame with bit number and D in step (1) _bvand R _bvbetween Mathematical Modeling, by linear regression solving equation group:

$\left[\begin{array}{c}{D}_{\mathrm{bv},0}^{-1}\\ \·\\ \·\\ \·\\ \·\\ \·\\ \·\\ D_{\mathrm{bv},W-1}^{-1}\end{array}\right]=a_{\mathrm{bv}}\left[\begin{array}{c}{R}_{\mathrm{bv},0}\\ \·\\ \·\\ \·\\ \·\\ \·\\ \·\\ R_{\mathrm{bv},W-1}\end{array}\right]+b_{\mathrm{bv}},$

Calculate the model parameter a of BV _bvand b _bv;

(4) according to the distortion of the NBV in the W frame before present frame with bit number $\stackrel{\→}{R_{\mathrm{nbv}}}=\{R_{\mathrm{nbv},0},...,R_{\mathrm{nbv},W-1}\},$ The bit number of BV $\stackrel{\→}{R_{\mathrm{bv}}}=\{R_{\mathrm{bv},0},...,R_{\mathrm{bv},W-1}\},$ And D in step (1) _nbvwith R _nbvand R _bvbetween Mathematical Modeling, by linear regression solving equation group:

$\left[\begin{array}{c}{(D_{\mathrm{nbv},0}-{\mathrm{\η}}_0{D}_{\mathrm{bv},0})}^{-1}\\ \·\\ \·\\ \·\\ \·\\ \·\\ \·\\ {(D_{\mathrm{nbv},W-1}-{\mathrm{\η}}_{W-1}{D}_{\mathrm{bv},W-1})}^{-1}\end{array}\right]=a_{\mathrm{nbv}}\left[\begin{array}{c}{R}_{\mathrm{nbv},0}\\ \·\\ \·\\ \·\\ \·\\ \·\\ \·\\ R_{\mathrm{nbv},W-1}\end{array}\right]+b_{\mathrm{nbv}},$

Wherein η ₀η _w-1represent that in encoded W frame, in 2 viewpoints of every frame, the distortion of BV, to the influence degree of the distortion of NBV, calculates the model parameter a of NBV _nbvand b _nbv;

(5) a of foundation step (3) and step (4) gained _bv, b _bv, a _nbv, b _nbv, and adopt total bit number R of rate control algorithm present frame _c, pass through following formula:

$R_{\mathrm{bv}}=\frac{R_c+\frac{b_{\mathrm{nbv}}}{a_{\mathrm{nbv}}}-\frac{b_{\mathrm{bv}}}{\sqrt{a_{\mathrm{bv}}{a}_{\mathrm{nbv}}(1+\mathrm{\η})}}}{1+\sqrt{\frac{a_{\mathrm{bv}}}{a_{\mathrm{nbv}}(1+\mathrm{\η})}}},$

$R_{\mathrm{nbv}}=\sqrt{\frac{a_{\mathrm{bv}}}{a_{\mathrm{nbv}}(1+\mathrm{\η})}}{R}_{\mathrm{bv}}+\frac{b_{\mathrm{bv}}}{\sqrt{a_{\mathrm{nbv}}{a}_{\mathrm{bv}}(1+\mathrm{\η})}}-\frac{b_{\mathrm{nbv}}}{a_{\mathrm{nbv}}},$

For BV and the NBV allocation bit number of present frame, namely calculate the R of present frame _bvand R _nbv;

(6) according to the principle of " first in first out ", by array vector the 0th data delete, and the coding distortion of present frame and number of coded bits are added to the end of array vector, upgrade array vector

(7) return step (3), next frame is encoded.

Effect of the present invention can further illustrate by experiment.

Experiment test under different bandwidth, the encoder bit rate after adopting the present invention to encode to multi-view point video and rebuild the overall objective quality (Y-PSNR, PSNR) of multi-view point video.Fig. 3 and Fig. 4 compares the rate distortion curve of the Bit distribution method adopting the present invention and fixed proportion.Wherein Fig. 3 is the experimental result of 2 viewpoint codings to three-dimensional video sequence Balloons, and Fig. 4 is the experimental result of 2 viewpoint codings to three-dimensional video sequence BookArrival.From Fig. 3 and Fig. 4, compared with the Bit distribution method of fixed proportion, after adopting the present invention to encode, under same-code code check, the total quality rebuilding multi-view point video is higher, and the coding efficiency that invention increases multi-view point video is described.

Claims (3)

1. a Bit distribution method between the viewpoint being applied to 2 viewpoint videos coding, is characterized in that, comprise the following steps:

(1) Mathematical Modeling defined between the coding distortion of basic viewpoint and number of coded bits is:

D _bv＝(a _bv(R _bv+b _bv) ^-1,

Wherein, D _bvrepresent the coding distortion of basic viewpoint, R _bvrepresent the number of coded bits of basic viewpoint, a _bvand b _bvfor model parameter, represent R _bvto D _bvinfluence degree; The coding distortion D of not substantially viewpoint _nbvwith the number of coded bits R of not substantially viewpoint _nbvwith the number of coded bits R of basic viewpoint _bvbetween pass be:

D _nbv＝η(a _bvR _bv+b _bv) ^-1+(a _nbvR _nbv+b _nbv) ^-1,

Wherein, η represents that the coding distortion of the basic viewpoint of present frame is to the influence degree of the coding distortion of NBV, a _nbvand b _nbvfor model parameter, represent R _nbvto D _nbvinfluence degree;

(2) W frame before multi-view video sequences being started most, rate control algorithm is adopted to determine the basic viewpoint of every frame and total bit number of not substantially viewpoint, and be different viewpoint allocation bit by the ratio preset and encode, the coding distortion of the basic viewpoint after coding and number of coded bits are stored in array vector respectively with in, coding distortion and the number of coded bits of not substantially viewpoint are stored in array vector respectively ${\stackrel{\→}{D}}_{\mathrm{nbv}}=\{D_{\mathrm{nbv},0},\·\·\·,D_{\mathrm{nbv},W-1}\}$ With ${\stackrel{\→}{R}}_{\mathrm{nbv}}=\{R_{\mathrm{nbv},0},\·\·\·,R_{\mathrm{nbv},W-1}\}$ In;

(3) according to the distortion of the basic viewpoint in the W frame before present frame with bit number and D in step (1) _bvand R _bvbetween Mathematical Modeling, by linear regression solving equation group:

$\left[\begin{array}{c}{D}_{\mathrm{bv},0}^{-1}\\ .\\ .\\ .\\ .\\ .\\ .\\ D_{\mathrm{bv},W-1}^{-1}\end{array}\right]=a_{\mathrm{bv}}\left[\begin{array}{c}{R}_{\mathrm{bv},0}\\ .\\ .\\ .\\ .\\ .\\ .\\ R_{\mathrm{bv},W-1}\end{array}\right]+{\text{b}}_{\mathrm{bv}},$

Calculate the model parameter a of basic viewpoint _bvand b _bv;

(4) according to the distortion of the not substantially viewpoint in the W frame before present frame with bit number ${\stackrel{\→}{R}}_{\mathrm{nbv}}=\{R_{\mathrm{nbv},0},\·\·\·,R_{\mathrm{nbv},W-1}\},$ The bit number of BV ${\stackrel{\→}{R}}_{\mathrm{bv}}=\{R_{\mathrm{bv},0},\·\·\·,R_{\mathrm{bv},W-1}\},$ And D in step (1) _nbvwith R _nbvand R _bvbetween Mathematical Modeling, by linear regression solving equation group:

$\left[\begin{array}{c}{(D_{\mathrm{nbv},0}-{\mathrm{\η}}_0{D}_{\mathrm{bv},0})}^{-1}\\ .\\ .\\ .\\ .\\ .\\ .\\ {(D_{\mathrm{nbv},W-1}-{\mathrm{\η}}_{W-1}{D}_{\mathrm{bv},W-1})}^{-1}\end{array}\right]=a_{\mathrm{nbv}}\left[\begin{array}{c}{R}_{\mathrm{nbv},0}\\ .\\ .\\ .\\ .\\ .\\ .\\ R_{\mathrm{nbv},W-1}\end{array}\right]+b_{\mathrm{nbv}},$

Wherein η ₀η _w-1represent that in encoded W frame, in 2 viewpoints of every frame, the distortion of basic viewpoint, to the influence degree of the distortion of not substantially viewpoint, calculates the model parameter a of not substantially viewpoint _nbvand b _nbv;

(5) a of foundation step (3) and step (4) gained _bv, b _bv, a _nbvand b _nbv, and adopt total bit number R of rate control algorithm present frame _c, pass through following formula:

$R_{\mathrm{bv}}=\frac{R_c+\frac{b_{\mathrm{nbv}}}{a_{\mathrm{nbv}}}-\frac{b_{\mathrm{bv}}}{\sqrt{a_{\mathrm{bv}}{a}_{\mathrm{nbv}}(1+\mathrm{\η})}}}{1+\sqrt{\frac{a_{\mathrm{bv}}}{a_{\mathrm{nbv}}(1+\mathrm{\η})}}},$

$R_{\mathrm{nbv}}=\sqrt{\frac{a_{\mathrm{bv}}}{a_{\mathrm{nbv}}(1+\mathrm{\η})}}{R}_{\mathrm{bv}}+\frac{b_{\mathrm{bv}}}{\sqrt{a_{\mathrm{nbv}}{a}_{\mathrm{bv}}(1+\mathrm{\η})}}-\frac{b_{\mathrm{nbv}}}{a_{\mathrm{nbv}}},$

For basic viewpoint and the not substantially viewpoint allocation bit number of present frame, namely calculate the R of present frame _bvand R _nbv;

(6) according to the principle of " first in first out ", by array vector the 0th data delete, and the coding distortion of present frame and number of coded bits are added to the end of array vector, upgrade array vector

(7) return step (3), next frame is encoded.

2. Bit distribution method between the viewpoint being applied to 2 viewpoint video codings according to claim 1, it is characterized in that, the η described in described step (1) is calculated by following formula:

$\mathrm{\η}=\frac{{\mathrm{Num}}_{\mathrm{PU}\_\mathrm{InterViewSKIPMode}}}{{\mathrm{Num}}_{\mathrm{PU}},}$

Wherein, Num _{pU_InterViewSKIPMode}represent in the not substantially viewpoint of present frame, adopt the quantity of the predicting unit of dancing mode coding between viewpoint, Num _pUrepresent in the not substantially viewpoint of present frame, the quantity of all predicting unit.

3. Bit distribution method between the viewpoint being applied to 2 viewpoint video codings according to claim 1, it is characterized in that, the ratio preset in described step (2) is: