用于转换许多元素的更快版本的 dec2bin 函数? [英] Faster version of dec2bin function for converting many elements?

问题描述

我正在读取一个位图文件并将 每个从 0 到 255 的 RGB 值转换为二进制.

I am reading a bitmap file and converting each of the RGB values ranging from 0 to 255 to binary.

因此，一个 240 x 320 的位图将有 230400 个 RGB 值进行转换.原来的 dec2bin 函数太慢了，所以我自己写了，因为我知道我的值总是在 0 到 255 之间.

So a 240 by 320 bitmap will have 230400 RGB values to convert. The original dec2bin function was too slow, so I wrote my own as I know my value will always be between 0 to 255.

但是通过 230400 个值仍然需要大约.在我的机器上是 6 秒，单色位图大约需要 2.3 秒.

But going through 230400 values will still take approx. 6sec on my machine, and a single colour bitmap will take about 2.3sec.

是否有任何方法可以将速度提高到 1 秒以下甚至更好的 0.5 秒，因为我的应用程序每毫秒都很重要?

Is there anyway to speed things up to be under 1sec or even better 0.5sec, as every msec counts for my application?

这是我的代码:

function s = dec2bin_2(input)

if input == 255
    s = [1;1;1;1;1;1;1;1];
    return;
end

s = [0;0;0;0;0;0;0;0];

if input == 0
    return;
end

if input >= 128
    input = input - 128;
    s(1) = 1;
    if input == 0
        return;
    end
end

if input >= 64
    input = input - 64;
    s(2) = 1;
    if input == 0
        return;
    end
end

if input >= 32
    input = input - 32;
    s(3) = 1;
    if input == 0
        return;
    end
end

if input >= 16
    input = input - 16;
    s(4) = 1;
    if input == 0
        return;
    end
end

if input >= 8
    input = input - 8;
    s(5) = 1;
    if input == 0
        return;
    end
end

if input >= 4
    input = input - 4;
    s(6) = 1;
    if input == 0
        return;
    end
end

if input >= 2
    input = input - 2;
    s(7) = 1;
    if input == 0
        return;
    else
        s(8) = 1;
    end
end
end

我在想，如果我不能在 MATLAB 中做到这一点，那么也许我会在 C++ 中进行转换.这是可取的吗?

I was thinking if I'm not able to do it in MATLAB then maybe I'll do the conversion in C++. Is this advisable?

谢谢.

推荐答案

更快的方法是使用查找表.由于您知道所有值都是 0 到 255 之间的强度，因此您可以构造每个值的二进制等效项以加快处理速度.

An even faster way is to use lookup tables. Since you know all the values are intensities between 0 and 255, you construct the binary equivalent of each to speed up the process.

% build table (computed once) [using gnovice option#1]
lookupTable = cell2mat(arrayfun(@(i)bitget([0:255]',9-i),1:8,'UniformOutput',0));

% random' image
I = randi(256, [240 320])-1;

% decimal to binary conversion
binI = lookupTable(I(:)+1,:);

在我的机器上，平均需要 0.0036329 秒(仅转换).注意查找表几乎没有空间开销:

On my machine, it took on average 0.0036329 seconds (only the conversion). Note the lookup table has almost no space overhead:

>> whos lookupTable
  Name               Size            Bytes  Class    Attributes
  lookupTable      256x8              2048  uint8 

这篇关于用于转换许多元素的更快版本的 dec2bin 函数?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！