Re: [libjpeg-turbo-users] Question About Grayscale Output

DRC Tue, 06 Jul 2021 08:07:34 -0700

uint8_t * is the same as unsigned char *, so the TurboJPEG API can readdirectly from that. libjpeg-turbo can also read directly from an arrayof uint8_t pointers, much like libpng can, but you would have to use thelibjpeg API rather than the TurboJPEG API in order to do that. I wouldsuggest that you avoid the uint8_t * --> uint8_t ** conversion unlessusing libpng.

On 7/5/21 10:32 PM, 'Kevin McBride' via libjpeg-turbo UserDiscussion/Support wrote:

In stick2xyz, there are three modules that the main program goesthrough to output an image file. The Input module reads the sourcedata that needs processing. The Pane2D module organizes the sourcedata into an image. And finally, the Output2D module takes the dataprocessed inside Pane2D and generates the image file.

In Pane2D, there is code that converts the stored image data fromuint8_t * to uint8_t **. The latter array is what libpng requires. Maybe I should make another function that can convert the uint8_t * todifferent formats, such as unsigned char * that JPEG Turbo requires.


https://sourceforge.net/p/stick2xyz/stick2xyz/HEAD/tree/trunk/stick2xyz/src/modules/pane2d/gen/propget.c

In that source file is where the conversion to uint8_t ** occurs.

- Kevin McBride
On Monday, July 5, 2021 at 11:14:20 AM UTC-4 DRC wrote:

    You can probably avoid that memcpy() and thus improve performance
    if you set the pitch argument to the actual distance between the
    rows in the multi-dimensional array, but without knowing the
    specifics of the multi-dimensional array, I couldn’t tell you the
    appropriate pitch to use.

    On Jul 4, 2021, at 3:38 PM, 'Kevin McBride' via libjpeg-turbo
    User Discussion/Support <libjpeg-t...@googlegroups.com> wrote:

    
    I found the problem in my code.  I was not correctly converting
    the image data into a single dimension unsigned char array.  I
    changed the code to the following, and I managed to get the
    PNG-style array converted into the array that TurboJPEG accepts. 
    I also corrected the pitch.

    srcbuf2 = srcbuf = (unsigned char *)calloc(x, y);
        if ( srcbuf == NULL )
            return 0;
        /* Fill the jpeg buffer. */
        for ( i=0; i < y; i++ )
        {
            memcpy(srcbuf2, image[i], x);
            srcbuf2 += x;
        }

    Now the image comes out looking the same as the PNG.  First image
    is the JPEG, second image is the PNG.
    <output00001.jpeg>
    <output00001.png>

    Thank you for the help, DRC.
    On Sunday, July 4, 2021 at 3:45:49 PM UTC-4 Kevin McBride wrote:

        I changed the call to tcCompress2 to the following and still
        do not get the expected result:

        tjCompress2(
                jpeghandle,
                srcbuf,
                x,
                x * tjPixelSize[TJPF_GRAY],
                y,

                TJPF_GRAY,
                &jpegBuf,
                &jpegSize,
                TJSAMP_GRAY,
                100,
                TJFLAG_STOPONWARNING)

        output00001.jpeg
        On Sunday, July 4, 2021 at 9:51:08 AM UTC-4 DRC wrote:

            At first glance, it appears as if you are setting the
            pitch argument incorrectly. Should that not be x * 1
            rather than y * 1?

            On Jul 3, 2021, at 8:48 PM, 'Kevin McBride' via
            libjpeg-turbo User Discussion/Support
            <libjpeg-t...@googlegroups.com> wrote:

            
            Good evening,

            I am working on my project stick2xyz
            http://sourceforge.net/projects/stick2xyz
            <http://sourceforge.net/projects/stick2xyz>
            and I have an image that is mirroring itself after the
            source buffer has been passed to tjCompress2 with the
            following args:

            tjCompress2(
                    jpeghandle,
                    srcbuf,
                    x,  // x is 320
                    y * 1,
                    y,  // y is 240
                    TJPF_GRAY,
                    &jpegBuf,
                    &jpegSize,
                    TJSAMP_GRAY,
                    100,
                    TJFLAG_STOPONWARNING)

            I am using version 2.0.90 from Fedora. Attached is the
            memory dump of srcbuf in hex as well as the output jpeg
            I got.

            I do not want the image data duplicated to the right of
            the image while in tjCompress2.


            <output00001.jpeg>

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            <test.txt>
            <output00001.jpeg>

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    <output00001.jpeg>
    <output00001.png>

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Re: [libjpeg-turbo-users] Question About Grayscale Output

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