Howdy, Stranger!

It looks like you're new here. If you want to get involved, click one of these buttons!

Supported by

[open] Pixelsize in Gabor patch generator

edited December 2013 in Miscellaneous

Hey!
I am using the online Gabor patch generator and I was wondering how to determine the size of the stimulus.
I know that the Gabor patch for my project needs to have a radius of 2° and I also determined the pixels per degree for our setting but I am not sure whether I need to convert the radius into pixels or whether I should use the diameter then (so 4°)? Or does the size asked for in the generator refer to the whole square and not just the Gabor patch within it?
Also, I am trying to use different contrast levels. I am not too familiar with this and I was wondering whether, if I want to have a background with the mean luminance, I would start with the RGB values for both colours at 128 as the lowest possible contrast and then stepwise increase the difference (e.g. colour 1: 129 and colour 2: 127) or whether the lowest possible contrast would be 127 to 128 and then increase/decrease (e.g. next contrast would be at 126 and 129). I used the latter at first but I wasn't too sure about it (as it is only possible to use integers for the generator, but then the average wouldn't be an integer) but then if I use the first approach the background doesn't really seem to look right.
I would be really grateful, if someone could help me out with these questions! :)

Comments

  • edited 1:12PM

    Hi Isabel,

    In theory, the size of a Gabor patch is infinite: The contrast is high in the center and becomes progressively lower with increasing eccentricity--but never exactly zero. So you would typically specify the size of a Gabor patch by the standard deviation of the envelope, and not by a radius. The 'size' option in the Gabor-patch generator is only the size of the generated image, which should be sufficiently large so that there is no visible cut off. Does that clear things up? I'm not sure if this answers your question though.

    Regarding the contrast. Using (127,127,127) for color 1 and (128,128,128) will indeed give you the lowest possible contrast. But the background color will be rounded up to 128, because the average (127.5) is not an integer and can therefore not be shown by the monitor. And for the same reason, the luminance modulation will not be a smooth sinusoid, but a square wave (i.e. a single step from one luminance to the next). Basically, with these extremely low contrast levels, you run into the physical limitations of the display. But since you usually work with far higher contrast levels, these problems are mostly theoretical. Is it important for your experiment to have high-quality extremely low contrast patches?

    Cheers!
    Sebastiaan

    Buy Me A Coffee

  • edited January 2014

    Hey Sebastiaan,

    I think this answers my questions, thank you very much for your help!
    For the contrasts, though, would it work to use a brighter background (if I use the average of the two colours), if I want to have smaller contrasts? So, for example using 244 for colour 1 and 246 for colour 2 etc.?

  • edited 1:12PM

    For the contrasts, though, would it work to use a brighter background (if I use the average of the two colours), if I want to have smaller contrasts? So, for example using 244 for colour 1 and 246 for colour 2 etc.?

    In principle, I would say that the contrast is defined as the difference in brightness between the two colors, and is unrelated to the overall brightness. So 10 and 12 would have the same contrast as 100 and 102. However, I suppose that this is open to debate.

    But at any rate, you cannot use values over 255, because this is outside the range of the monitor. I just noticed that the Gabor-patch will not warn you about this (except in the description), but choosing values over 255 will cause odd distortions!

    Cheers!
    Sebastiaan

    Buy Me A Coffee

Sign In or Register to comment.

agen judi bola , sportbook, casino, togel, number game, singapore, tangkas, basket, slot, poker, dominoqq, agen bola. Semua permainan bisa dimainkan hanya dengan 1 ID. minimal deposit 50.000 ,- bonus cashback hingga 10% , diskon togel hingga 66% bisa bermain di android dan IOS kapanpun dan dimana pun. poker , bandarq , aduq, domino qq , dominobet. Semua permainan bisa dimainkan hanya dengan 1 ID. minimal deposit 10.000 ,- bonus turnover 0.5% dan bonus referral 20%. Bonus - bonus yang dihadirkan bisa terbilang cukup tinggi dan memuaskan, anda hanya perlu memasang pada situs yang memberikan bursa pasaran terbaik yaitu http://45.77.173.118/ Bola168. Situs penyedia segala jenis permainan poker online kini semakin banyak ditemukan di Internet, salah satunya TahunQQ merupakan situs Agen Judi Domino66 Dan BandarQ Terpercaya yang mampu memberikan banyak provit bagi bettornya. Permainan Yang Di Sediakan Dewi365 Juga sangat banyak Dan menarik dan Peluang untuk memenangkan Taruhan Judi online ini juga sangat mudah . Mainkan Segera Taruhan Sportbook anda bersama Agen Judi Bola Bersama Dewi365 Kemenangan Anda Berapa pun akan Terbayarkan. Tersedia 9 macam permainan seru yang bisa kamu mainkan hanya di dalam 1 ID saja. Permainan seru yang tersedia seperti Poker, Domino QQ Dan juga BandarQ Online. Semuanya tersedia lengkap hanya di ABGQQ. Situs ABGQQ sangat mudah dimenangkan, kamu juga akan mendapatkan mega bonus dan setiap pemain berhak mendapatkan cashback mingguan. ABGQQ juga telah diakui sebagai Bandar Domino Online yang menjamin sistem FAIR PLAY disetiap permainan yang bisa dimainkan dengan deposit minimal hanya Rp.25.000. DEWI365 adalah Bandar Judi Bola Terpercaya & resmi dan terpercaya di indonesia. Situs judi bola ini menyediakan fasilitas bagi anda untuk dapat bermain memainkan permainan judi bola. Didalam situs ini memiliki berbagai permainan taruhan bola terlengkap seperti Sbobet, yang membuat DEWI365 menjadi situs judi bola terbaik dan terpercaya di Indonesia. Tentunya sebagai situs yang bertugas sebagai Bandar Poker Online pastinya akan berusaha untuk menjaga semua informasi dan keamanan yang terdapat di POKERQQ13. Kotakqq adalah situs Judi Poker Online Terpercayayang menyediakan 9 jenis permainan sakong online, dominoqq, domino99, bandarq, bandar ceme, aduq, poker online, bandar poker, balak66, perang baccarat, dan capsa susun. Dengan minimal deposit withdraw 15.000 Anda sudah bisa memainkan semua permaina pkv games di situs kami. Jackpot besar,Win rate tinggi, Fair play, PKV Games